The Portable Enlightenment Reader - Isaac Kramnick (1995)




In this selection from his 1620 book, Novum Organum, Francis Bacon (1561-1626), English philosopher of science, essayist, and statesman, spells out the scientific methodology that would so influence the Enlightenment.

Man, being the servant and interpreter of Nature, can do and understand so much and so much only as he has observed in fact or in thought of the course of nature: beyond this he neither knows anything nor can do anything.

Neither the naked hand nor the understanding left to itself can effect much. It is by instruments and helps that the work is done, which are as much wanted for the understanding as for the hand. And as the instruments of the hand either give motion or guide it, so the instruments of the mind supply either suggestions for the understanding or cautions.

Human knowledge and human power meet in one, for where the cause is not known the effect cannot be produced. Nature to be commanded must be obeyed; and that which in contemplation is as the cause is in operation as the rule.

The subtlety of nature is greater many times over than the subtlety of the senses and understanding; so that all those specious meditations, speculations, and glosses in which men indulge are quite from the purpose, only there is no one by to observe it.

The logic now in use serves rather to fix and give stability to the errors which have their foundation in commonly received notions than to help the search after truth. So it does more harm than good.

The syllogism is not applied to the first principles of sciences, and is applied in vain to intermediate axioms; being no match for the subtlety of nature. It commands assent therefore to the proposition, but does not take hold of the thing.

The syllogism consists of propositions, propositions consist of words, words are symbols of notions. Therefore if the notions themselves (which is the root of the matter) are confused and overhastily abstracted from the facts, there can be no firmness in the superstructure. Our only hope therefore lies in a true induction.

There is no soundness in our notions whether logical or physical. Substance, Quality, Action, Passion, Essence itself, are not sound notions: much less are Heavy, Light, Dense, Rare, Moist, Dry, Generation, Corruption, Attraction, Repulsion, Element, Matter, Form, and the like; but all are fantastical and ill defined.

The conclusions of human reason as ordinarily applied in matter of nature, I call for the sake of distinction Anticipations of Nature (as a thing rash or premature). That reason which is elicited from facts by a just and methodical process, I call Interpretation of Nature.

Anticipations are a ground sufficiently firm for consent; for even if men went mad all after the same fashion, they might agree one with another well enough.

For the winning of assent, indeed, anticipations are far more powerful than interpretations; because being collected from a few instances, and those for the most part of familiar occurrence, they straightway touch the understanding and fill the imagination; whereas interpretations on the other hand, being gathered here and there from very various and widely dispersed facts, cannot suddenly strike the understanding; and therefore they must needs, in respect of the opinions of the time, seem harsh and out of tune; much as the mysteries of faith do.

In sciences founded on opinions and dogmas, the use of anticipations and logic is good; for in them the object is to command assent to the proposition, not to master the thing.

Though all the wits of all the ages should meet together and combine and transmit their labors, yet will no great progress ever be made in science by means of anticipations; because radical errors in the first concoction of the mind are not to be cured by the excellence of functions and remedies subsequent.

It is idle to expect any great advancement in science from the superinducing and engrafting of new things upon old. We must begin anew from the very foundations, unless we would revolve forever in a circle with mean and contemptible progress.

The honor of the ancient authors, and indeed of all, remains untouched; since the comparison I challenge is not of wits or faculties, but of ways and methods, and the part I take upon myself is not that of a judge, but of a guide.

This must be plainly avowed: no judgment can be rightly formed either of my method or of the discoveries to which it leads, by means of anticipations (that is to say, of the reasoning which is now in use); since I cannot be called on to abide by the sentence of a tribunal which is itself on its trial.

The doctrine of those who have denied that certainty could be attained at all, has some agreement with my way of proceeding at the first setting out; but they end in being infinitely separated and opposed. For the holders of that doctrine assert simply that nothing can be known; I also assert that not much can be known in nature by the way which is now in use. But then they go on to destroy the authority of the senses and understanding; whereas I proceed to devise and supply helps for the same.

The idols and false notions which are now in possession of the human understanding, and have taken deep root therein, not only so beset men’s minds that truth can hardly find entrance, but even after entrance obtained, they will again in the very instauration of the sciences meet and trouble us, unless men being forewarned of the danger fortify themselves as far as may be against their assaults.

There are four classes of Idols which beset men’s minds. To these for distinction’s sake I have assigned names—calling the first class Idols of the Tribe; the second, Idols of the Cave; the third, Idols of the Market Place; the fourth, Idols of the Theater.

The formation of ideas and axioms by true induction is no doubt the proper remedy to be applied for the keeping off and clearing away of idols. To point them out, however, is of great use; for the doctrine of Idols is to the Interpretation of Nature what the doctrine of the refutation of Sophisms is to common Logic.

The Idols of the Tribe have their foundation in human nature itself, and in the tribe or race of men. For it is a false assertion that the sense of man is the measure of things. On the contrary, all perceptions as well of the sense as of the mind are according to the measure of the individual and not according to the measure of the universe. And the human understanding is like a false mirror, which, receiving rays irregularly, distorts and discolors the nature of things by mingling its own nature with it.

The Idols of the Cave are the idols of the individual man. For everyone (besides the errors common to human nature in general) has a cave or den of his own, which refracts and discolors the light of nature; owing either to his own proper and peculiar nature; or to his education and conversation with others; or to the reading of books, and the authority of those whom he esteems and admires, or to the differences of impressions, accordingly as they take place in a mind preoccupied and predisposed or in a mind indifferent and settled; or the like. So that the spirit of man (according as it is meted out to different individuals) is in fact a thing variable and full of perturbation, and governed as it were by chance. Whence it was well observed by Heraclitus that men look for sciences in their own lesser worlds, and not in the greater or common world.

There are also Idols formed by the intercourse and association of men with each other, which I call Idols of the Market Place, on account of the commerce and consort of men there. For it is by discourse that men associate; and words are imposed according to the apprehension of the vulgar. And therefore the ill and unfit choice of words wonderfully obstructs the understanding. Nor do the definitions or explanations wherewith in some things learned men are wont to guard and defend themselves, by any means set the matter right. But words plainly force and overrule the understanding, and throw all into confusion, and lead men away into numberless empty controversies and idle fancies.

Lastly, there are Idols which have immigrated into men’s minds from the various dogmas of philosophies, and also from wrong laws of demonstration. These I call Idols of the Theater; because in my judgment all the received systems are but so many stage plays, representing worlds of their own creation after an unreal and scenic fashion. Nor is it only of the systems now in vogue, or only of the ancient sects and philosophies, that I speak; for many more plays of the same kind may yet be composed and in like artificial manner set forth; seeing that errors the most widely different have nevertheless causes for the most part alike. Neither again do I mean this only of entire systems, but also of many principles and axioms in science, which by tradition, credulity, and negligence have come to be received.



Sir Isaac Newton (1642-1727), professor of mathematics at Cambridge University, personified science and its rationalist ideals for the eighteenth century. The following is an excerpt from his monumental Principia, written in Latin in 1687.


Definition I

The quantity of matter is the measure of the same, arising from its density and bulk conjointly.

Thus air of a double density, in a double space, is quadruple in quantity; in a triple space, sextuple in quantity. The same thing is to be understood of snow, and fine dust or powders, that are condensed by compression or liquefaction, and of all bodies that are by any causes whatever differently condensed. I have no regard in this place to a medium, if any such there is, that freely pervades the interstices between the parts of bodies. It is this quantity that I mean hereafter everywhere under the name of body or mass. And the same is known by the weight of each body, for it is proportional to the weight, as I have found by experiments on pendulums, very accurately made, which shall be shown hereafter.

Definition II

The quantity of motion is the measure of all the same, arising from the velocity and quantity of matter conjointly.

The motion of the whole is the sum of the motion of all the parts; and therefore in a body double in quantity, with equal velocity, the motion is double; with twice the velocity, it is quadruple....

Definition IV

An impressed force is an action exerted upon a body, in order to change its state, either of rest, or of uniform motion in a right line.

This force consists in the action only, and remains no longer in the body when the action is over. For a body maintains every new state it acquires, by its inertia only. But impressed forces are of different origins, as from percussion, from pressure, from centripetal force....

Definition VI

The absolute quantity of a centripetal force is the measure of the same, proportional to the efficacy of the cause that propagates it from the center, through the spaces round about.

Thus the magnetic force is greater in one loadstone and less in another, according to their sizes and strength of intensity.

Definition VII

The accelerative quantity of a centripetal force is the measure of the same, proportional to the velocity which it generates in a given time.

Thus the force of the same loadstone is greater at a less distance, and less at a greater: also the force of gravity is greater in valleys, less on tops of exceedingly high mountains; and yet less, at greater distances from the body of the earth; but at equal distances, it is the same everywhere; because (taking away, allowing for, the resistance of air), it equally accelerates all falling bodies, whether heavy or light, great or small....


Law I

Every body continues in its state of rest, or of uniform motion, in a right line, unless it is compelled to change that state by forces impressed upon it.

Projectiles continue in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity. A top, whose parts by their cohesion are continually drawn aside from rectilinear motions, does not cease its rotation, otherwise than as it is retarded by the air. The greater bodies of the planets and comets, meeting with less resistance in freer spaces, preserve their motions both progressive and circular for a much longer time.

Law II

The change of motion is proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed.

If any force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subtracted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are oblique, so as to produce a new motion compounded from the determination of both.


To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts.

Whatever draws or presses another is as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may say so) will be equally drawn back towards the stone; for the distended rope, by the same endeavor to relax or unbend itself, will draw the horse as much towards the stone as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. If a body impinge upon another, and by its force change the motion of the other, that body also (because of the equality of the mutual pressure) will undergo an equal change, in its own motion, towards the contrary part. The changes made by these actions are equal, not in the velocities but in the motions of the bodies; that is to say, if the bodies are not hindered by any other impediments. For, because the motions are equally changed, the changes of the velocities made toward contrary parts are inversely proportional to the bodies....


Rule I

We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.

To this purpose the philosophers say that Nature does nothing in vain, and more is in vain when less will serve; for Nature is pleased with simplicity, and affects not the pomp of superfluous causes.

Rule II

Therefore to the same natural effects we must, as far as possible, assign the same causes.

As to respiration in a man and in a beast; the descent of stones in Europe and in America; the light of our culinary fire and of the sun; the reflection of light in the earth, and in the planets.

Rule III

The qualities of bodies, which admit neither intensification nor remission of degrees, and which are found to belong to all bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.

For since the qualities of bodies are only known to us by experiments, we are to hold for universal all such as universally agree with experiments; and such as are not liable to diminution can never be quite taken away. We are certainly not to relinquish the evidence of experiments for the sake of dreams and vain fictions of our own devising; nor are we to recede from the analogy of Nature, which is wont to be simple, and always consonant to itself. We no other way know the extension of bodies than by our senses, nor do these reach it in all bodies; but because we perceive extension in all that are sensible, therefore we ascribe it universally to all others also. That abundance of bodies are hard, we learn by experience; and because the hardness of the whole arises from the hardness of the parts, we therefore justly infer the hardness of the undivided particles not only of the bodies we feel but of all others. That all bodies are impenetrable, we gather not from reason but from sensation. The bodies which we handle we find impenetrable, and thence conclude impenetrability to be a universal property of all bodies whatsoever. That all bodies are movable, and endowed with certain power (which we call the inertia) of persevering in their motion, or in their rest, we only infer from the like properties observed in the bodies which we have seen. The extension, hardness, impenetrability, mobility, and inertia of the whole, result from the extension, hardness, impenetrability, mobility, and inertia of the parts; and hence we conclude the least particles of all bodies to be also all extended, and hard and impenetrable, and movable, and endowed with their proper inertia. And this is the foundation of all philosophy. Moreover, that the divided but contiguous particles of bodies may be separated from one another, is matter of observation; and, in the particles that remain undivided, our minds are able to distinguish yet lesser parts, as is mathematically demonstrated. But whether the parts so distinguished, and not yet divided, may, by the powers of Nature, be actually divided and separated from one another, we cannot certainly determine. Yet, had we the proof of but one experiment that any undivided particle, in breaking a hard and solid body, suffered a division, we might by virtue of this rule conclude that the undivided as well as the divided particles may be divided and actually separated to infinity.

Lastly, if it universally appears, by experiments and astronomical observations, that all bodies about the earth gravitate towards the earth, and that in proportion to the quantity of matter which they severally contain; that the moon likewise, according to the quantity of its matter, gravitates towards the earth; that, on the other hand, our sea gravitates towards the moon; and all the planets one towards another; and the comets in like manner towards the sun; we must, in consequence of this rule, universally allow that all bodies whatsoever are endowed with a principle of mutual gravitation. For the arguments from the appearances concludes with more force for the universal gravitation of all bodies than for their impenetrability; of which, among those in the celestial regions, we have no experiments, nor any manner of observation. Not that I affirm gravity to be essential to bodies: by their vis insita I mean nothing but their inertia. This is immutable. Their gravity is diminished as they recede from the earth.

Rule IV

In experimental philosophy we are to look upon propositions inferred by general induction from phenomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions.

This rule we must follow, that the argument of induction may not be evaded by hypotheses.



English astronomer and mathematician Roger Cotes (1682-1716wrote the preface to the second edition of Newton’s Principia in 1713, from which this section is taken.

Those who have treated of natural philosophy may be nearly reduced to three classes. Of these some have attributed to the several species of things specific and occult qualities, on which, in a manner unknown, they make the operations of the several bodies to depend. The sum of the doctrine of the Schools derived from Aristotle and the Peripatetics is herein contained. They affirm that the several effects of bodies arise from the particular natures of those bodies. But whence it is that bodies derive those natures they don’t tell us; and therefore they tell us nothing. And being entirely employed in giving names to things, and not in searching into things themselves, we may say that they have invented a philosophical way of speaking, but not that they have made known to us true philosophy....

There is left then the third class, which profess experimental philosophy. These indeed derive the causes of all things from the most simple principles possible; but then they assume nothing as a principle that is not proved by phenomena. They frame no hypotheses, nor receive them into philosophy otherwise than as questions whose truth may be disputed. They proceed therefore in a twofold method, synthetical and analytical. From some select phenomena they deduce by analysis the forces of nature, and the more simple laws of forces; and from thence by synthesis show the constitution of the rest. This is that incomparably best way of philosophizing, which our renowned author most justly embraced before the rest; and thought alone worthy to be cultivated and adorned by his excellent labors. Of this he has given us a most illustrious example, by the explication of the System of the World, most happily deduced from the Theory of Gravity. That the virtue of gravity was found in all bodies, others suspected, or imagined before him; but he was the only and the first philosopher that could demonstrate it from appearances, and make it a solid foundation to the most noble speculations.

Therefore that we may begin our reasoning from what is most simple and nearest to us, let us consider a little what is the nature of gravity with us on Earth, that we may proceed the more safely when we come to consider it in the heavenly bodies that lie at so vast a distance from us. It is now agreed by all philosophers that all circumterrestrial bodies gravitate towards the Earth. That no bodies really light are to be found is now confirmed by manifold experience. That which is relative levity is not true levity, but apparent only, and arises from the preponderating gravity of the contiguous bodies.

Moreover, as all bodies gravitate towards the Earth, so does the Earth again towards bodies. That the action of gravity is mutual, and equal on both sides, is thus proved....

This is the nature of gravity upon Earth; let us now see what it is in the Heavens.

That every body perseveres in its state either of rest, or of moving uniformly in a right line, unless insofar as it is compelled to change that state by forces impressed, is a law of nature universally received by all philosophers. But from thence it follows that bodies which move in curve lines, and are therefore continually going off from the right lines that are tangents to their orbits, are by some continued force retained in those curvilinear paths. Since then the planets move in curvilinear orbits, there must be some force operating by whose repeated actions they are perpetually made to deflect from the tangents....

From what has been hitherto said, it is plain that the planets are retained in their orbits by some force perpetually acting upon them; it is plain that that force is always directed towards the centers of their orbits; it is plain that its efficacy is augmented with the nearness to the center, and diminished with the same; and that it is augmented in the same proportion with which the square of the distance is diminished, and diminished in the same proportion with which the square of the distance is augmented....

Because the revolutions of the primary planets about the Sun, and of the secondary about Jupiter and Saturn, are phenomena of the same kind with the revolution of the Moon about the Earth; and because it has been moreover demonstrated that the centripetal forces of the primary planets are directed towards the center of the Sun, and those of the secondary towards the centers of Jupiter and Saturn, in the same manner as the centripetal force of the Moon is directed towards the center of the Earth; and since besides, all these forces are reciprocally as the squares of the distances from the centers, in the same manner as the centripetal force of the Moon is as the square of the distance from the Earth; we must of course conclude that the nature of all is the same. Therefore as the Moon gravitates towards the Earth, and the Earth again towards the Moon; so also all the secondary planets will gravitate towards their primary, and the primary planets again towards their secondary; and so all the primary towards the Sun; and the Sun again towards the primary.

Therefore the Sun gravitates towards all the planets, and all the planets towards the Sun....

That the attractive virtue of the Sun is propagated on all sides to prodigious distances, and is diffused to every part of the wide space that surrounds it, is most evidently shown by the motion of the comets; which coming from places immensely distant from the Sun, approach very near to it; and sometimes so near, that in their perihelia they almost touch its body. The theory of these bodies was altogether unknown to astronomers, till in our own times our excellent author most happily discovered it, and demonstrated the truth of it by most certain observations. So that it is now apparent that the comets move in conic sections having their foci in the Sun’s center, and by radii drawn to the Sun describe areas proportional to the times. But from these phenomena it is manifest, and mathematically demonstrated, that those forces, by which the comets are retained in their orbits, respect the Sun, and are reciprocally proportional to the squares of the distances from its center. Therefore the comets gravitate towards the Sun; and therefore the attractive force of the Sun not only acts on the bodies of the planets, placed at given distances and very nearly in the same plane, but reaches also to the comets in the most different parts of the heavens, and at the most different distances. This therefore is the nature of gravitating bodies, to propagate their force at all distances to all other gravitating bodies.

The foregoing conclusions are grounded on this axiom which is received by all philosophers; namely that effects of the same kind, that is, whose known properties are the same, take their rise from the same causes and have the same unknown properties also. For who doubts, if gravity be the cause of the descent of a stone in Europe, but that it is also the cause of the same descent in America? ...

Since then all bodies, whether upon Earth or in the heavens, are heavy, so far as we can make any experiments or observations concerning them; we must certainly allow that gravity is found in all bodies universally. And in like manner as we ought not to suppose that any bodies can be otherwise than extended, moveable or impenetrable, so we ought not to conceive that any bodies can be otherwise than heavy. The extension, mobility, and impenetrability of bodies become known to us only by experiments; and in the very same manner their gravity becomes known to us. All bodies we can make any observations upon are extended, moveable, and impenetrable; and thence we conclude all bodies, and those we have no observations concerning, to be extended and moveable and impenetrable. So all bodies we can make observations on we find to be heavy; and thence we conclude all bodies, and those we have no observations of, to be heavy also. If anyone should say that the bodies of the fixed stars are not heavy because their gravity is not yet observed; they may say for the same reason that they are neither ex,tended nor moveable nor impenetrable, because these affections of the fixed stars are not yet observed. In short, either gravity must have a place among the primary qualities of all bodies, or extension, mobility and impenetrability must not.



More than any other philosophe, Voltaire (1694-1778) helped to popularize English writers and science in general to his French readers. The following excerpts are from his Letters Concerning the English Nation, published in 1733.

It is not long since the ridiculous and threadbare question was agitated in a celebrated assembly; who was the greatest man, Caesar or Alexander, Tamerlane or Cromwell? Somebody said that it must undoubtedly be Sir Isaac Newton. This man was certainly in the right; for if true greatness consists in having received from heaven the advantage of a superior genius, with the talent of applying it for the interest of the possessor and of mankind, a man like Newton—and such a one is hardly to be met with in ten centuries—is surely by much the greatest; and those statesmen and conquerors which no age has ever been without, are commonly but so many illustrious villains. It is the man who sways our minds by the prevalence of reason and the native force of truth, not they who reduce mankind to a state of slavery by brutish force and downright violence; the man who by the vigor of his mind, is able to penetrate into the hidden secrets of nature, and whose capacious soul can contain the vast frame of the universe, not those who lay nature waste, and desolate the face of the earth, that claims our reverence and admiration.

Therefore, as you are desirous to be informed of the great men that England has produced, I shall begin with the Bacons, the Lockes, and the Newtons. The generals and ministers will come after them in their turn.

I must begin with the celebrated baron Verulam, known to the rest of Europe by the name of Bacon, who was the son of a certain keeper of the seals, and was for a considerable time chancellor under James I. Notwithstanding the intrigues and bustle of a court, and the occupations incident to his office, which would have required his whole attention, he found means to become a great philosopher, a good historian, and an elegant writer; and what is yet more wonderful is that he lived in an age where the art of writing was totally unknown, and where sound philosophy was still less so. This personage, as is the way among mankind, was more valued after his death than while he lived. His enemies were courtiers residing at London, while his admirers consisted wholly of foreigners. When Marquis d‘Effiat brought Princess Mary, daughter of Henry the Great, over to be married to King Charles, this minister paid Bacon a visit, who being then confined to a sick bed, received him with close curtains. “You are like the angels,” said d’Effiat to him; “we hear much talk of them, and while everybody thinks them superior to men, we are never favored with a sight of them.”

You have been told in what manner Bacon was accused of a crime which is very far from being the sin of a philosopher, of being corrupted by pecuniary gifts; and how he was sentenced by the house of peers to pay a fine of about four hundred thousand livres of our money, besides losing his office of chancellor, and being degraded from the rank and dignity of a peer. At present the English revere his memory to such a degree that only with great difficulty can one imagine him to have been in the least guilty. Should you ask me what I think of it, I will make use of a saying I heard from Lord Bolingbroke. They happened to be talking of the avarice with which the duke of Marlborough had been taxed, and quoted several instances of it, for the truth of which they appealed to Lord Bolingbroke, who, as being of a contrary party, might, perhaps, without any trespass against the laws of decorum, freely say what he thought. “He was,” said he, “so great a man that I do not recollect whether he had any faults or not.” I shall, therefore, confine myself to those qualities which have acquired Chancellor Bacon the esteem of all Europe.

The most singular, as well as the most excellent, of all his works, is that which is now the least read, and which is at the same time the most useful; I mean his “Novum Scientiarum Organum.” This is the scaffold by means of which the edifice of the new philosophy has been reared; so that when the building was completed, the scaffold was no longer of any use. Chancellor Bacon was still unacquainted with nature, but he perfectly knew, and pointed out extraordinarily well, all the paths which lead to her recesses. He had very early despised what those square-capped fools teach in those dungeons called Colleges, under the name of philosophy, and did everything in his power that those bodies, instituted for the cultivation and perfection of the human understanding, might cease any longer to mar it, by their “quiddities,” their “horrors of a vacuum,” their “substantial forms,” with the rest of that jargon which ignorance and a nonsensical jumble of religion had consecrated.

This great man is the father of experimental philosophy. It is true, wonderful discoveries had been made even before his time; the mariner’s compass, the art of printing, that of engraving, the art of painting in oil, that of making glass, with the remarkably advantageous invention of restoring in some measure sight to the blind; that is, to old men, by means of spectacles; the secret of making gunpowder had, also, been discovered. They had gone in search of, discovered, and conquered a new world in another hemisphere. Who would not have thought that these sublime discoveries had been made by the greatest philosophers, and in times much more enlightened than ours? By no means; for all these astonishing revolutions happened in the ages of scholastic barbarity. Chance alone has brought forth almost all these inventions; it is even pretended that chance has had a great share in the discovery of America; at least, it has been believed that Christopher Columbus undertook this voyage on the faith of a captain of a ship who had been cast by a storm on one of the Caribbee islands. Be this as it will, men had learned to penetrate to the utmost limits of the habitable globe, and to destroy the most impregnable cities with an artificial thunder, much more terrible than the real; but they were still ignorant of the circulation of the blood, the weight and pressure of the air, the laws of motion, the doctrine of light and color, the number of the planets in our system, etc. And a man that was capable to maintain a thesis on the “Categories of Aristotle,” the universale a parte rei, or such-like nonsense, was considered as a prodigy.

The most wonderful and useful inventions are by no means those which do most honor to the human mind. And it is to a certain mechanical instinct, which exists in almost every man, that we owe far the greater part of the arts, and in no manner whatever to philosophy. The discovery of fire, the arts of making bread, of melting and working metals, of building houses, the invention of the shuttle, are infinitely more useful than printing and the compass; notwithstanding, all these were invented by men who were still in a state of barbarity. What astonishing things have the Greeks and Romans since done in mechanics? Yet men believed, in their time, that the heavens were of crystal, and the stars were so many small lamps, that sometimes fell into the sea; and one of their greatest philosophers, after many researches, had at length discovered that the stars were so many pebbles, that had flown off like sparks from the earth.

In a word, there was not a man who had any idea of experimental philosophy before Chancellor Bacon; and of an infinity of experiments which have been made since his time, there is hardly a single one which has not been pointed out in his book. He had even made a good number of them himself. He constructed several pneumatic machines, by which he discovered the elasticity of the air; he had long brooded over the discovery of its weight, and was even at times very near to catching it, when it was laid hold of by Torricelli. A short time after, experimental physics began to be cultivated in almost all parts of Europe. This was a hidden treasure, of which Bacon had some glimmerings, and which all the philosophers whom his promises had encouraged made their utmost efforts to lay open. We see in his book mention made in express terms of that new attraction of which Newton passes for the inventor. “We must inquire,” said Bacon, “whether there be not a certain magnetic force, which operates reciprocally between the earth and other heavy bodies, between the moon and the ocean, between the planets, etc.” In another place he says: “Either heavy bodies are impelled toward the center of the earth, or they are mutually attracted by it; in this latter case it is evident that the nearer falling bodies approach the earth, the more forcibly are they attracted by it. We must try,” continues he, “whether the same pendulum clock goes faster on the top of a mountain, or at the bottom of a mine. If the force of the weight diminishes on the mountain, and increases in the mine, it is probable the earth has a real attracting quality.”

This precursor in philosophy was also an elegant writer, a historian, and a wit. His moral essays are in high estimation, though they seem rather calculated to instruct than to please; and as they are neither a satire on human nature, like the maxims of Rochefoucauld, nor a school of skepticism, like Montaigne, they are not so much read as these two ingenious books. His life of Henry VII passed for a masterpiece; but how is it possible some people should have been idle enough to compare so small a work with the history of our illustrious M. de Thou? Speaking of that famous impostor Perkin, son of a Jew convert, who assumed so boldly the name of Richard IV, king of England, being encouraged by the duchess of Burgundy, and who disputed the crown with Henry VII, he expresses himself in these terms: “About this time King Henry was beset with evil spirits, by the witchcraft of the duchess of Burgundy, who conjured up from hell the ghost of Edward IV, in order to torment King Henry. When the duchess of Burgundy had instructed Perkin, she began to consider with herself in what region of the heavens she should make this comet shine, and resolved immediately that it should make its appearance in the horizon of Ireland.” I think our sage de Thou seldom gives in to this gallimaufry, which used formerly to pass for the sublime, but which at present is known by its proper title, “bombast.” ...


A Frenchman who arrives in London will find philosophy, like everything else, very much changed there. He had left the world a plenum, and he now finds it a vacuum. At Paris the universe is seen composed of vortices of subtle matter; but nothing like it is seen in London. In France it is the pressure of the moon that causes the tides; but in England it is the sea that gravitates towards the moon; so that when you think that the moon should make it flood with us, those gentlemen fancy it should be ebb, which, very unluckily, cannot be proved. For to be able to do this it is necessary the moon and the tides should have been enquired into at the very instant of the Creation.

You’ll observe farther that the sun, which in France is said to have nothing to do in the affair, comes in here for very near a quarter of its assistance. According to your Cartesians, everything is performed by an impulsion, of which we have very little notion; and according to Sir Isaac Newton, it is by an attraction, the cause of which is as much unknown to us. At Paris you imagine that the earth is shaped like a melon, or of an oblique figure; at London it has an oblate one. A Cartesian declares that light exists in the air; but a Newtonian asserts that it comes from the sun in six minutes and a half. The several operations of your chemistry are performed by acids, alkalies and subtile matter; but attraction prevails even in chymistry among the English.

The very essence of things is totally changed. You neither are agreed upon the definition of the soul nor on that of matter. Descartes, as I observed in my last, maintains that the soul is the same thing with thought, and Mr. Locke has given a pretty good proof of the contrary.

Descartes asserts farther, that extension alone constitutes matter, but Sir Isaac adds solidity to it.

How furiously contradictory are these opinions!

Non nostrum inter vos tantas componere lites. VIRGIL, ECLOG. III.

’Tis not for us to end such great Disputes.

This famous Newton, this destroyer of the Cartesian system, died in March Anno 1727. His countrymen honored him in his lifetime, and interred him as though he had been a king who had made his people happy.

The English read with the highest satisfaction, and translated into their tongue, the elogium of Sir Isaac Newton which Mr. de Fontenelle spoke in the Academy of Sciences. Mr. de Fontenelle presides as judge over philosophers; and the English expected his decision as a solemn declaration of the superiority of the English philosophy over that of the French. But when it was found that this gentleman had compared Descartes to Sir Isaac, the whole Royal Society in London rose up in arms. So far from acquiescing with Mr. de Fontenelle’s judgment, they criticized his discourse. And even several (who, however, were not the ablest philosophers in that body) were offended at the comparison, and for no other reason but because Descartes was a Frenchman.

It must be confessed that these two great men differed very much in conduct, in fortune, and in philosophy.

Nature had indulged Descartes a shining and strong imagination, whence he became a very singular person both in private life and in his manner of reasoning. This imagination could not conceal itself even in his philosophical works, which are everywhere adorned with very shining, ingenious metaphors and figures. Nature had almost made him a poet; and indeed he wrote a piece of poetry for the entertainment of Christina, Queen of Sweden, which, however, was suppressed in honor to his memory.

He embraced a military life for some time, and afterwards becoming a complete philosopher, he did not think the passion of love derogatory to his character. He had by his mistress a daughter called Froncine, who died young and was very much regretted by him. Thus he experienced every passion incident to mankind.

He was a long time of the opinion that it would be necessary for him to fly from the society of his fellow creatures, and especially from his native country, in order to enjoy the happiness of cultivating his philosophical studies in full liberty.

Descartes was very right, for his contemporaries were not knowing enough to improve and enlighten his understanding, and were capable of little else than of giving him uneasiness.

He left France purely to go in search of truth, which was then persecuted by the wretched philosophy of the Schools. However, he found that reason was as much disguised and depraved in the universities of Holland, into which he withdrew, as in his own country. For at the time that the French condemned the only propositions of his philosophy which were true, he was persecuted by the pretended philosophers of Holland, who understood him no better, and who, having a nearer view of his glory, hated his person the more, so that he was obliged to leave Utrecht. Descartes was injuriously accused of being an atheist, the last refuge of religious scandal; and he who had employed all the sagacity and penetration of his genius in searching for new proofs of the existence of a God was suspected to believe there was no such Being.

Such a persecution from all sides must necessarily suppose a most exalted merit as well as a very distinguished reputation, and indeed he possessed both. Reason at that time darted a ray upon the world through the gloom of the Schools and the prejudices of popular superstition. At last his name spread so universally that the French were desirous of bringing him back into his native country by rewards, and accordingly offered him an annual pension of a thousand crowns. Upon these hopes Descartes returned to France, paid the fees of his patent, which was sold at that time, but no pension was settled upon him. Thus disappointed, he returned to his solitude in North Holland, where he again pursued the study of philosophy, whilst the great Galileo, at fourscore years of age, was groaning in the prisons of the Inquisition, only for having demonstrated the earth’s motion.

At last Descartes was snatched from the world in the flower of his age at Stockholm. His death was owing to a bad regimen, and he expired in the midst of some literati who were his enemies, and under the hands of a physician to whom he was odious.

The progress of Sir Isaac Newton’s life was quite different. He lived happy and very much honored in his native country, to the age of fourscore and five years.

It was his peculiar felicity not only to be born in a country of liberty, but in an age when all Scholastic impertinencies were banished from the world. Reason alone was cultivated, and mankind could only be his pupil, not his enemy.

One very singular difference in the lives of these two great men is that Sir Isaac, during the long course of years he enjoyed, was never sensible to any passion, was not subject to the common frailties of mankind, nor ever had any commerce with women; a circumstance which was assured me by the physician and surgeon who attended him in his last moments.

We may admire Sir Isaac Newton on this occasion, but then we must not censure Descartes.

The opinion that generally prevails in England with regard to these two philosophers is that the latter was a dreamer and the former a sage.

Very few people in England read Descartes, whose works indeed are now useless. On the other side, but a small number peruse those of Sir Isaac, because to do this the student must be deeply skilled in the mathematics, otherwise those works will be unintelligible to him. But notwithstanding this, these great men are the subject of everyone’s discourse. Sir Isaac Newton is allowed every advantage, whilst Descartes is not indulged a single one. According to some, it is to the former that we owe the discovery of a vacuum, that the air is a heavy body, and the invention of telescopes. In a word, Sir Isaac Newton is here as the Hercules of fabulous story, to whom the ignorant ascribed all the feats of ancient heroes.

In a critique that was made in London on Mr. de Fontenelle’s discourse, the writer presumed to assert that Descartes was not a great geometrician. Those who make such a declaration may justly be reproached with flying in their master’s face. Descartes extended the limits of geometry as far beyond the place where he found them as Sir Isaac did after him. The former first taught the method of expressing curves by equations. This geometry, which, thanks to him for it, is now grown common, was so abstruse in his time that not so much as one professor would undertake to explain it; and Schotten in Holland, and Format in France, were the only men who understood it.

He applied this geometrical and inventive genius to dioptrics, which, when treated of by him, became a new art. And if he was mistaken in some things, the reason of that is, a man who discovers a new tract of land cannot at once know all the properties of the soil. Those who come after him, and make these Lands fruitful, are at least obliged to him for the discovery. I will not deny but that there are innumerable errors in the rest of Descartes’s works.

Geometry was a guide he himself had in some measure fashioned, which would have conducted him safely through the several paths of natural philosophy. Nevertheless he at last abandoned this guide, and gave entirely into the humor of forming hypotheses; and then philosophy was no more than an ingenious romance, fit only to amuse the ignorant. He was mistaken in the nature of the soul, in the proofs of the existence of a God, in matter, in the laws of motion, and in the nature of light. He admitted innate ideas, he invented new elements, he created a world; he made Man according to his own fancy; and it is justly said that the Man of Descartes is in fact that of Descartes only, very different from the real one.

He pushed his metaphysical errors so far as to declare that two and two make four for no other reason but because God would have it so. However, it will not be making him too great a compliment if we affirm that he was valuable even in his mistakes. He deceived himself, but then it was at least in a methodical way. He destroyed all the absurd chimaeras with which youth had been infatuated for two thousand years. He taught his contemporaries how to reason, and enabled them to employ his own weapons against himself. If Descartes did not pay in good money, he however did great service in crying down that of a base alloy.

I indeed believe that very few will presume to compare his philosophy in any respect with that of Sir Isaac Newton. The former is an essay, the latter a masterpiece. But then the man who first brought us to the path of truth was perhaps as great a genius as he who afterwards conducted us through it.

Descartes gave sight to the blind. These saw the errors of antiquity and of the sciences. The path he struck out is since become boundless. Rohault’s little work was during some years a complete system of physics; but now all the transactions of the several academies in Europe put together do not form so much as the beginning of a system. In fathoming this abyss no bottom has been found. We are now to examine what discoveries Sir Isaac Newton has made in it.



Classification, minute observation, and factual description are essential to scientific inquiry. Georges Louis Leclerc, comte de Buffon (1707- 1788), was a French naturalist recognized as a master of this genre. The following is an excerpt from his Natural History of Animals, Vegetables and Minerals, written in 1767.

If we descend by degrees from the great to the small, from the strong to the weak, we shall find that Nature has uniformly maintained a balance; that, attentive only to the preservation of each species, she creates a profusion of individuals, and is supported by the numbers which she has formed of a diminutive size, and which she has denied weapons, denied either strength or courage; and that she has not only taken care that these inferior species should be in a condition to resist, or to maintain their ground by the abundance of their own number, but has likewise provided a supplement, as it were, to each, by multiplying the species which nearly resemble or approach them. The rat, the mouse, the mulot, or field-mouse, the water-rat, the campagnol, or little field rat, the loir, or great dor-mouse, the lerot, or middle dor-mouse; the muscardin, or small dor-mouse, the musaraigne, or shrew-mouse, with many others which I shall not enumerate here, as they are strangers to our climate, form so many distinct and separate species, but yet so little varied, that should any of the others fail, they might so well supply their places that their absence would be hardly perceptible. It is this great number of approximate species that first gave naturalists the idea of genera; an idea which can never be employed unless when we view objects in the gross, and which vanishes when we come to consider Nature minutely, and as she really is.

Men began by appropriating different names to things which appeared to them absolutely distinct and different, and at the same time they gave general denominations to such as seemed to bear a near resemblance to each other. Among nations rude and unenlightened, and in all infant languages, there are hardly any but general names, that is to say, vague and unformed expressions of things which, though of the same order, are yet in themselves highly different. Thus, the oak, the beech, the linden, the fir, the yew, the pine, had at first no name but that of tree; afterwards the oak, the beech, the linden, were all three called oak, when they came to be distinguished from the fir, the pine, and the yew, which in like manner would be distinguished by the name of fir. Particular names proceeded solely, in process of time, from the comparison and minute examination of things. Of these the number was encreased in proportion as the works of Nature were more studied, and better understood; and the more we shall continue to examine and compare them, the greater number there will be of proper names, and of particular denominations. When in these days, therefore, Nature is presented to us by general denominations, that is, by genera, it is sending us back to the ABC, or first rudiments of all knowledge, and to the infant-darkness of mankind. Ignorance produced genera,and science produced, and will continue to produce, proper names; nor of these shall we be afraid to increase the number, whenever we shall have occasion to denote different species.

Under the generical name of rat, people have comprised and confounded several species of little animals. This name we shall solely appropriate to the common rat, which is black, and lives in our houses. Each of the other species shall have its particular denomination; for as neither of them couple together, each is, in reality, different from all the rest. The rat is well enough known by the trouble he gives us. It generally inhabits barns, and other places where corn and fruit are stored; and from these it proceeds, and invades our dwellings. This animal is carnivorous, and even, if the expression is allowable, omnivorous. Hard substances, however, it prefers to soft ones: it devours wool, stuffs, and furniture of all sorts; eats through wood, makes hiding places in walls, thence issues in search of prey, and frequently returns with as much as it is able to drag along with it, forming, especially when it has young ones to provide for, a magazine of the whole. The females bring forth several times in the year, though mostly in the summer season; and they usually produce five or six at a birth. They search for warm places; and in winter they generally shelter themselves about the chimnies of houses, or among hay and straw.

In defiance of the cats, and notwithstanding the poison, the traps, and every other method that is used to destroy these creatures, they multiply so fast as frequently to do considerable damage. In old houses in the country especially, where great quantities of corn are kept, and where the neighboring barns and haystacks favor their retreat, as well as their multiplication, they are often so numerous that the inhabitants would be obliged to remove with their furniture, were they not to devour each other. This we have often by experience found to be the case when they have been in any degree straitened for provisions; and the method they take to lessen their numbers is for the stronger to fall upon the weaker. This done, they lay open their skulls, and first eat up the brains, afterwards the rest of the body. The next day hostilities are renewed in the same manner; nor do they suspend their havoc till the majority are destroyed. For this reason it is that after any place has for a long while been infested with rats, they often seem to disappear of a sudden, and sometimes for a considerable time. It is the same with the field-mice, whose prodigious encrease is checked solely by their cruelties towards each other, when they begin to be in want of food. Aristotle attributes this sudden destruction to the rain; but rats are not exposed to the weather, and field-mice know well how to secure themselves from it, their subterranean habitations being never even moistened.

The rat is an animal as salacious as it is voracious. They have a kind of yelp when they engender; and when they fight, they cry. They prepare a bed for their young, and provide them immediately with food. On their first quitting the hole, she watches over, defends, and will even fight the cats, in order to save them. A large rat is more mischievous, and almost as strong, as a young cat. Its foreteeth are long and strong; and as the cat does not bite so hard, as she can do little execution except with her claws, she must be not only vigorous, but well experienced to conquer. The weasel, though smaller in size, is yet a more dangerous enemy to the rat, and is more feared by it, because he is capable of following it into its hiding-places. The combat between these two animals is generally sharp and long; their strength is at least equal, but their manner of fighting is different. The rat cannot inflict any wounds but by snatches, and with its foreteeth, which, however, being rather calculated for gnawing than for biting, have but little strength; whereas the weasel bites fiercely with the force of its whole jaw at once, and instead of letting go its hold, sucks the blood through the wound. In every conflict with an enemy so formidable, it is no wonder, therefore, that the rat should fall a victim.

There are many varieties in this as in every other species of which the individuals are very numerous. Beside the common black rat there are some which are brown, and some almost black; some which are grey, inclining to white or red, and some altogether white. The white rat, like the white mouse, the white rabbit, and all other animals which are entirely of that color, has red eyes. The white species, with all its varieties, appears to belong to the temperate climates of our continent, and have been diffused in much greater abundance over hot countries than cold ones. Originally they had none in America; and those which are to be found there in such numbers at this day are the produce of rats which accidentally obtained a footing on the other side of the Atlantic with the first European settlers. Of these the increase was so great that the rat was long considered as the pest of the colonies; where indeed it had hardly an enemy to oppose it but the large adder, which swallows it up alive. The European ships have likewise carried these animals to the East Indies, into all the islands of the Indian Archipelago, as well as into Africa, where they are found in great numbers. In the North, on the contrary, they have hardly multiplied beyond Sweden; and those which are called Norway rats, in Lapland, etc., are animals different from our rats.



Condorcet was a distinguished mathematician as well as political activist and writer. In the ninth stage of his Sketch for a Historical Picture of the Human Mind (1794), he offered a veritable hymn to science and its usefulness in human affairs.

We may endeavor more especially to trace that practice of genius in the sciences which at one time descends from an abstract and profound theory to learned and delicate applications; at another, simplifying its means, and proportioning them to its wants, concludes by spreading its advantages through the most ordinary practices; it plunges into the most remote speculations, in fear of resources which the ordinary state of our knowledge must have refused.

We may remark that those arguments which are made against the utility of theories, even in the most simple arts, have never shown any thing but the ignorance of the declaimers. We may prove that it is not to the profundity of these theories, but, on the contrary, to their imperfection, that we ought to attribute the inutility or unhappy effects of so many useless applications.

These observations will lead us to one general truth, that in all the arts the results of theory are necessarily modified in practice; that certain sources of inaccuracy exist, which are really inevitable, of which our aim should be to render the effect insensible, without indulging the chimerical hope of removing them; that a great number of data relative to our wants, our means, our time, and our expenses, which are necessarily overlooked in the theory, must enter into the relative problem of immediate and real practice; and that, lastly, by introducing these requisites with that skill which truly constitutes the genius of the practical man, we may at the same time go beyond the narrow limits wherein prejudice against theory threatens to detain the arts, and prevent those errors into which an improper use of theory might lead us.

Those sciences which are remote from each other cannot be extended without bringing them nearer and forming points of contact between them.

An exposition of the progress of each science is sufficient to show that in several the intermediate application of numbers has been useful, as, in almost all, it has been employed to give a greater degree of precision to experiments and observations; and that the sciences are indebted to mechanics, which has supplied them with more perfect and more accurate instruments. How much have the discovery of microscopes, and of meteorological instruments, contributed to the perfection of natural history? How greatly is this science indebted to chemistry, which, alone, has been sufficient to lead to a more profound knowledge of the objects it considers, by displaying their most intimate nature, and most essential properties—by showing their composition and elements; while natural history offers to chemistry so many operations to execute, such a numerous set of combinations formed by nature, the true elements of which require to be separated, and sometimes discovered, by an imitation of the natural processes; and, lastly, how great is the mutual assistance afforded to each other by chemistry and natural philosophy; and how greatly have anatomy and natural history been already benefited by these sciences.

But we have yet exposed no more than a small portion of the advantages which have been received, or may be expected, from these applications.

Many geometers have given us general methods of deducing, from observations of the empiric laws of phenomena, methods which extend to all the sciences; because they are in all cases capable of affording us the knowledge of the law of the successive values of the same quantity, for a series of instants or positions; or that law according to which they are distributed, or which is followed by the various properties and values of a similar quality among a given number of objects.

Applications have already proved, that the science of combination may be successfully employed to dispose observations, in such a manner, that their relations, results, and sum may with more facility be seen.

The uses of the calculation of probabilities foretell how much they may be applied to advance the progress of other sciences; in one case, to determine the probability of extraordinary facts, and to show whether they ought to be rejected, or whether, on the contrary, they ought to be verified; or in calculating the probability of the return of those facts which often present themselves in the practice of the arts, and are not connected together in an order, yet considered as a general law. Such, for example, in medicine, is the salutary effect of certain remedies, and the success of certain preservatives. These applications likewise show us how great is the probability that a series of phenomena should result from the intention of a thinking being; whether this being depends on other co-existent, or antecedent phenomena; and how much ought to be attributed to the necessary and unknown cause denominated chance, a word the sense of which can only be known with precision by studying this method of computing.

The sciences have likewise taught us to ascertain the several degrees of certainty to which we may hope to attain; the probability according to which we can adopt an opinion, and make it the basis of our reasonings, without injuring the rights of sound argument, and the rules of our conduct—without deficiency in prudence, or offense to justice. They show what are the advantages or disadvantages of various forms of election, and modes of decision dependent on the plurality of voices; the different degrees of probability which may result from such proceedings; the method which public interest requires to be followed, according to the nature of each question; the means of obtaining it nearly with certainty, when the decision is not absolutely necessary, or when the inconveniences of two conclusions being unequal, neither of them can become legitimate until beneath this probability; or the assurance beforehand of most frequently obtaining this same probability, when, on the contrary, a decision is necessary to be made, and the most feeble preponderance of probability is sufficient to produce a rule of practice.

Among the number of these applications we may likewise state, an examination of the probability of facts for the use of such as have not the power, or means, to support their conclusions upon their own observations; a probability which results either from the authority of witnesses, or the connection of those facts with others immediately observed.

How greatly have inquiries into the duration of human life, and the influence in this respect of sex, temperature, climate, profession, government, and habitudes of life; on the mortality which results from different diseases; the changes which population experiences; the extent of the action of different causes which produce these changes; the manner of its distribution in each country, according to the age, sex, and occupation—how greatly useful have these researches been to the physical knowledge of man, to medicine, and to public economy.

How extensively have computations of this nature been applied for the establishment of annuities, tontines, accumulating funds, benefit societies, and chambers of assurance of every kind.

Is not the application of numbers also necessary to that part of the public economy which includes the theory of public measures, of coin, of banks and financial operations, and lastly, that of taxation, as established by law, and its real distribution, which so frequently differs, in its effects on all the parts of the social system.

What a number of important questions in this same science are there, which could not have been properly resolved without the knowledge acquired in natural history, agriculture, and the philosophy of vegetables, which influence the mechanical or chemical arts.

In a word, such has been the general progress of the sciences, that it may be said there is not one which can be considered as to the whole extent of its principles and detail, without our being obliged to borrow the assistance of all the others.

In presenting this sketch both of the new facts which have enriched the sciences respectively, and the advantages derived in each from the application of theories, or methods, which seem to belong more particularly to another department of knowledge, we may endeavor to ascertain what is the nature and the limits of those truths to which observation, experience, or meditation, may lead us in each science; we may likewise investigate what it is precisely that constitutes that talent of invention which is the first faculty of the human mind, and is known by the name of genius; by what operations the understanding may attain the discoveries it pursues, or sometimes be led to others not sought, or even possible to have been foretold; we may show how far the methods which lead to discovery may be exhausted, so that science may, in a certain respect, be at a stand, till new methods are invented to afford an additional instrument to genius, or to facilitate the use of those which cannot be employed without too great a consumption of time and fatigue.

If we confine ourselves to exhibit the advantages deduced from the sciences in their immediate use or application to the arts, whether for the welfare of individuals or the prosperity of nations, we shall have shown only a small part of the benefits they afford. The most important perhaps is, that prejudice has been destroyed, and the human understanding in some sort rectified; after having been forced into a wrong direction by absurd objects of belief, transmitted from generation to generation, taught at the misjudging period of infancy, and enforced with the terrors of superstition and the dread of tyranny.

All the errors in politics and in morals are founded upon philosophical mistakes, which, themselves, are connected with physical errors. There does not exist any religious system, or supernatural extravagance, which is not founded on an ignorance of the laws of nature. The inventors and defenders of these absurdities could not foresee the successive progress of the human mind. Being persuaded that the men of their time knew everything they would ever know, and would always believe that in which they then had fixed their faith; they confidently built their reveries upon the general opinions of their own country and their own age.

The progress of natural knowledge is yet more destructive of these errors, because it frequently destroys them without seeming to attack them, by attaching to those who obstinately defend them the degrading ridicule of ignorance.

At the same time, the just habit of reasoning on the object of these sciences, the precise ideas which their methods afford, and the means of ascertaining or proving the truth, must naturally lead us to compare the sentiment which forces us to adhere to opinions founded on these real motives of credibility, and that which attaches us to our habitual prejudices, or forces us to yield to authority. This comparison is sufficient to teach us to mistrust these last opinions, to show that they were not really believed, even when that belief was the most earnestly and the most sincerely professed. When this discovery is once made, their destruction becomes much more speedy and certain.

Lastly, this progress of the physical sciences, which the passions and interest do not interfere to disturb; wherein it is not thought that birth, profession, or appointment have given a right to judge what the individual is not in a situation to understand; this more certain progress cannot be observed, unless enlightened men shall search in the other sciences to bring them continually together. This progress at every step exhibits the model they ought to follow; according to which they may form a judgment of their own efforts, ascertain the false steps they may have taken, preserve themselves from pyrrhonism as well as credulity, and from a blind mistrust or too extensive submission to the authorities even of men of reputation and knowledge.

The metaphysical analysis would, no doubt, lead to the same results, but it would have afforded only abstract principles. In this method, the same abstract principles being put into action, are enlightened by example and fortified by success.

Until the present epoch, the sciences have been the patrimony only of a few; but they are already become common, and the moment approaches in which their elements, their principles, and their most simple practice will become really popular. Then it will be seen how truly universal their utility will be in their application to the arts, and their influence on the general rectitude of the mind.



One of the Enlightenment’s greatest scientists was the Englishman Joseph Priestley (1733-1804), the discoverer of oxygen. Convinced that America was the natural home of the scientific spirit, Priestley emigrated there and is today buried in Northumberland, Pennsylvania. The selection that follows, his proposal for systematic scientific research, is from his History and Present State of Electricity (1767).

The business of [natural] philosophy is so multiplied, that all the books of general philosophical transactions cannot be purchased by many persons, or read by any person. It is high time to subdivide the business, that every man may have an opportunity of seeing everything that relates to his own favorite pursuit; and all the various branches of philosophy would find their account in this amicable separation. Thus the numerous branches of a large overgrown family, in the patriarchical ages, found it necessary to separate; and the convenience of the whole, and the strength and increase of each branch were promoted by the separation. Let the youngest daughter of the science set the example to the rest, and show that she thinks herself considerable enough to make her appearance in the world without the company of her sisters.

But before this general separation, let each collect together everything that belongs to her, and march off with her whole stock. To drop the allusion; let histories be written of all that has been done in every particular branch of science, and let the whole be seen at one view. And when once the entire progress, and present state of every science shall be fully and fairly exhibited, I doubt not but we shall see a new and capital era commence in the history of all the sciences. Such an easy, full, and comprehensive view of what has been done hitherto could not fail to give new life to philosophical enquiries. It would suggest an infinity of new experiments, and would undoubtedly greatly accelerate the progress of knowledge; which is at present retarded, as it were, by its own weight, and the mutual entanglement of its several parts.

I will just throw out a farther hint, of what, I think, might be favorable to the increase of philosophical knowledge. At present there are, in different countries in Europe, large incorporate societies, with funds for promoting philosophical knowledge in general. Let philosophers now begin to subdivide themselves, and enter into smaller combinations. Let the several companies make small funds, and appoint a director of experiments. Let every member have a right to appoint the trial of experiments in some proportion to the sum he subscribes, and let a periodical account be published of the result of them all, successful or unsuccessful. In this manner, the powers of all the members would be united and increased. Nothing would be left untried, which could be compassed at a moderate expense, and it being one person’s business to attend to these experiments, they would be made, and reported without loss of time. Moreover, as all incorporations in these smaller societies should be avoided, they would be encouraged only in proportion as they were found to be useful; and success in smaller things would excite them to attempt greater.

I by no means disapprove of large, general, and incorporated societies. They have their peculiar uses too; but we see by experience, that they are apt to grow too large, and their forms are too slow for the dispatch of the minutiæ of business, in the present multifarious state of philosophy. Let recourse be had to rich incorporated societies, to defray the expense of experiments, to which the funds of smaller societies shall be unequal. Let their transactions contain a summary of the more important discoveries, collected from the smaller periodical publications. Let them, by rewards, and other methods, encourage those who distinguish themselves in the inferior societies; and thus give a general attention to the whole business of philosophy.

I wish all the incorporated philosophical societies in Europe would join their funds (and I wish they were sufficient for the purpose) to fit out ships for the complete discovery of the face of the earth, and for many capital experiments which can only be made in such extensive voyages.

Princes will never do this great business to any purpose. The spirit of adventure seems to be totally extinct in the present race of merchants. This discovery is a grand desideratum in science; and where may this pure and noble enthusiasm for such discoveries be expected but among philosophers, men uninfluenced by motives either of policy or gain? Let us think ourselves happy if princes give no obstruction to such designs. Let them fight for the countries when they are discovered, and let merchants scramble for the advantage that may be made of them. It will be an acquisition to philosophers if the seat of war be removed so far from the seat of science; and fresh room will be given to the exertion of genius in trade, when the old beaten track is deserted, when the old system of traffic is unhinged, and when new and more extensive plans of commerce take place. I congratulate the present race of philosophers on what is doing by the English court in this way; for with whatever view expeditions into the South Seas are made, they cannot but be favorable to philosophy.

Natural Philosophy is a science which more especially requires the aid of wealth. Many others require nothing but what a man’s own reflection may furnish him with. They who cultivate them find within themselves everything they want. But experimental philosophy is not so independent. Nature will not be put out of her way, and suffer her materials to be thrown into all that variety of situations which philosophy requires, in order to discover her wonderful powers, without trouble and expense. Hence the patronage of the great is essential to the flourishing state of this science. Others may project great improvements, but they only have the power of carrying them into execution.

Besides, they are the higher classes of men which are most interested in the extension of all kinds of natural knowledge; as they are most able to avail themselves of any discoveries, which lead to the felicity and embellishment of human life. Almost all the elegancies of life are the produce of those polite arts, which could have had no existence without natural science, and which receive daily improvements from the same source. From the great and the opulent, therefore, these sciences have a natural claim for protection; and it is evidently their interest not to suffer promising enquiries to be suspended for want of the means of prosecuting them.

But other motives, besides this selfish one, may reasonably be supposed to attach persons in the higher ranks of life to the sciences; motives more exalted, and flowing from the most extensive benevolence. From Natural Philosophy have flowed all those great inventions, by means of which mankind in general are able to subsist with more ease, and in greater numbers upon the face of the earth. Hence arise the capital advantages of men above brutes, and of civilization above barbarity. And by these sciences also it is, that the views of the human mind itself are enlarged, and our common nature improved and ennobled. It is for the honor of the species, therefore, that these sciences should be cultivated with the utmost attention.

And of whom may these enlarged views, comprehensive of such great objects, be expected, but of those whom divine providence has raised above the rest of mankind. Being free from most of the cares peculiar to individuals, they may embrace the interests of the whole species, feel for the wants of mankind, and be concerned to support the dignity of human nature.

Gladly would I indulge the hope, that we shall soon see these motives operating in a more extensive manner than they have hitherto done; that by the illustrious example of a few, a taste for natural science will be excited in many, in whom it will operate the most effectually to the advantage of science and of the world; and that all kinds of philosophical enquiries will, henceforward, be conducted with more spirit, and with more success than ever.

Were I to pursue this subject, it would carry me far beyond the reasonable bounds of a preface. I shall therefore conclude with mentioning that sentiment, which ought to be uppermost in the mind of every philosopher, whatever be the immediate object of his pursuit; that speculation is only of use as it leads to practice, that the immediate use of natural science is the power it gives us over nature, by means of the knowledge we acquire of its laws; whereby human life is, in its present state, made more comfortable and happy; but that the greatest, and noblest use of philosophical speculation is the discipline of the heart, and the opportunity it affords of inculcating benevolent and pious sentiments upon the mind.

A philosopher ought to be something greater, and better than another man. The contemplation of the works of God should give a sublimity to his virtue, should expand his benevolence, extinguish everything mean, base, and selfish in his nature, give a dignity to all his sentiments, and teach him to aspire to the moral perfections of the great author of all things. What great and exalted beings would philosophers be, would they but let the objects about which they are conversant have their proper and moral effect upon their minds! A life spent in the contemplation of the productions of divine power, wisdom, and goodness, would be a life of devotion. The more we see of the wonderful structure of the world, and of the laws of nature, the more clearly do we comprehend their admirable uses, to make all the percipient creation happy: a sentiment, which cannot but fill the heart with unbounded love, gratitude and joy.

Even everything painful and disagreeable in the world appears to a philosopher, upon a more attentive examination, to be excellently provided, as a remedy of some greater inconvenience, or a necessary means of a much greater happiness; so that, from this elevated point of view, he sees all temporary evils and inconveniences to vanish, in the glorious prospect of the greater good to which they are subservient. Hence he is able to venerate and rejoice in God, not only in the bright sunshine, but also in the darkest shades of nature, whereas vulgar minds are apt to be disconcerted with the appearance of evil.



Internationally renowned as a scientist, statesman, and writer, Franklin (1706-1790) in this letter articulates the quintessential Enlightenment utopian vision of science as the handmaiden of progress.

PASSY, Feb. 8, 1780.


Your kind letter of September 27 came to hand but very lately, the bearer having stayed long in Holland. I always rejoice to hear of your being still employed in experimental researches into nature, and of the Success you meet with. The rapid Progress true Science now makes, occasions my regretting sometimes that I was bom so soon. It is impossible to imagine the height to which may be carried, in a thousand years, the power of man over matter. We may perhaps learn to deprive large masses of their gravity, and give them absolute levity, for the sake of easy transport. Agriculture may diminish its labor and double its produce; all diseases may by sure means be prevented or cured, not excepting even that of old age, and our lives lengthened at pleasure even beyond the antediluvian standard. O that moral science were in as fair a way of improvement, that men would cease to be wolves to one another, and that human beings would at length learn what they now improperly call humanity!

I am glad my little paper on the Aurora Borealis pleased. If it should occasion further enquiry, and so produce a better hypothesis, it will not be wholly useless. I am ever, with the greatest and most sincere esteem, dear sir, yours very affectionately