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Primary Sources – Unit Seven – Scientific Revolution & the Enlightenment

Commentariolus: Copernicus Outlines His Thesis

Nicolaus Copernicus


Our ancestors assumed, I observe, a large number of celestial spheres for this reason especially, to explain the apparent motion of the planets by the principle of regularity. For they thought it altogether absurd that a heavenly body, which is a perfect sphere, should not always move uniformly. They saw that by connecting and combining regular motions in various ways they could make any body appear to move to any position.

Callippus and Eudoxus, who endeavored to solve the problem by the use of concentric spheres, were unable to account for all the planetary movements; they had to explain not merely the apparent revolutions of the planets but also the fact that these bodies appear to us sometimes to mount higher in the heavens, sometimes to descend; and this fact is incompatible with the principle of concentricity. Therefore it seemed better to employ eccentrics and epicycles, a system which most scholars finally accepted.

Yet the planetary theories of Ptolemy and most other astronomers, although consistent with the numerical data, seemed likewise to present no small difficulty. For these theories were not adequate unless certain equants were also conceived; it then appeared that a planet moved with uniform velocity neither on its deferent nor about the center of its epicycle. Hence a system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind.

Having become aware of these defects, I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent inequality would be derived and in which everything would move uniformly about its proper center, as the rule of absolute motion requires. After I had addressed myself to this very difficult and almost insoluble problem, the suggestion at length came to me how it could be solved with fewer and much simpler constructions than were formerly used, if some assumptions (which are called axioms) were granted me. They follow in this order.


1. There is no one center of all the celestial circles or spheres.

2. The center of the earth is not the center of the universe, but only of gravity and of the lunar sphere.

3. All the spheres revolve about the sun as their mid-point, and therefore the sun is the center of the universe.

4. The ratio of the earth’s distance from the sun to the height of the firmament is so much smaller than the ratio of the earth’s radius to its distance from the sun that the distance from the earth to the sun is imperceptible in comparison with the height of the firmament.

5. Whatever motion appears in the firmament arises not from any motion of the firmament, but from the earth’s motion. The earth together with its circumjacent elements performs a complete rotation on its fixed poles in a daily motion, while the firmament and highest heaven abide unchanged.

6. What appear to us as motions of the sun arise not from its motion but from the motion of the earth and our sphere, with which we revolve about the sun like any other planet. The earth has, then, more than one motion.

7. The apparent retrograde and direct motion of the planets arises not from their motion but from the earth’s. The motion of the earth alone, therefore, suffices to explain so many apparent inequalities in the heavens.

Having set forth these assumptions, I shall endeavor briefly to show how uniformity of the motions can be saved in a systematic way. However, I have thought it well, for the sake of brevity, to omit from this sketch mathematical demonstrations, reserving these for my larger work. But in the explanation of the circles I shall set down here the lengths of the radii; and from these the reader who is not unacquainted with mathematics will readily perceive how closely this arrangement of circles agrees with the numerical data and observations.

Accordingly, let no one suppose that I have gratuitously asserted, with the Pythagoreans, the motion of the earth; strong proof will be found in my exposition of the circles. For the principal arguments by which the natural philosophers attempt to establish the immobility of the earth rest for the most part on the appearances; it is particularly such arguments that collapse here, since I treat the earth’s immobility as due to an appearance.

Editing Copernicus: The Preface to De Revolutionibus

Andres Osiander


To the Reader Concerning the Hypotheses of This Work:

There have already been widespread reports about the novel hypotheses of this work, which declares that the earth moves whereas the sun is at rest in the center of the universe. Hence certain scholars, I have no doubt, are deeply offended and believe that the liberal arts, which were established long ago on a sound basis, should not be thrown into confusion. But if these men are willing to examine the matter closely, they will find that the author of this work has done nothing blameworthy. For it is the duty of an astronomer to compose the history of the celestial motions through careful and expert study. Then he must conceive and devise the causes of these motions or hypotheses about them. Since he cannot in any way attain to the true causes, he will adopt whatever suppositions enable the motions to be computed correctly from the principles of geometry for the future as well as the past. The present author has performed both these duties excellently. For these hypotheses need not be true nor even probable. On the contrary, if they provide a calculus consistent with the observations, that alone is enough. Perhaps there is someone who is so ignorant of geometry and optics that he regards the epicycle of Venus as probable, or thinks that it is the reason why Venus sometimes precedes and sometimes follows the sun by forty degrees and even more. Is there anyone who is not aware that from this assumption it necessarily follows that the diameter of the planet at perigee should appear more than four times, and the body of the planet more than sixteen times, as great as at apogee? Yet this variation is refuted by the experience of every age. In this science there are some other no less important absurdities, which need not be set forth at the moment. For this art, it is quite clear, is completely and absolutely ignorant of the causes of the apparent nonuniform motions. And if any causes are devised by the imagination, as indeed very many are, they are not put forward to convince anyone that they are true, but merely to provide a reliable basis for computation. However, since different hypotheses are sometimes offered for one and the same motion (for example, eccentricity and an epicycle for the sun’s motion), the astronomer will take as his first choice that hypothesis which is the easiest to grasp. The philosopher will perhaps rather seek the semblance of the truth. But neither of them will understand or state anything certain, unless it has been divinely revealed to him.

Therefore alongside the ancient hypotheses, which are no more probable, let us permit these new hypotheses also to become known, especially since they are admirable as well as simple and bring with them a huge treasure of very skillful observations. So far as hypotheses are concerned, let no one expect anything certain from astronomy, which cannot furnish it, lest he accept as the truth ideas conceived for another purpose, and depart from this study a greater fool than when he entered it. Farewell.

Galileo Discovers the Moons of Jupiter

Galileo Galilei


On the seventh day of January in this present year 1610, at the first hour of night, when I was viewing the heavenly bodies with a telescope, Jupiter presented itself to me; and because I had prepared a very excellent instrument for myself, I perceived (as I had not before, on account of the weakness of my previous instrument) that beside the planet there were three starlets, small indeed, but very bright. Though I believed them to be among the host of fixed stars, they aroused my curiosity somewhat by appearing to lie in an exact straight line parallel to the ecliptic, and by their being more splendid than others of their size. Their arrangement with respect to Jupiter and each other was the following:

East * * O * West

that is, there were two stars on the eastern side and one to the west … on January eighth–led by what, I do not know–I found a very different arrangement. The three starlets were now all to the west of Jupiter, closer together, and at equal intervals from one another as shown in the following sketch:

East O * * * West

At this time, though I did not yet turn my attention to the way the stars had come together, I began to concern myself with the question how Jupiter could be east of all these stars when on the previous day it had been west of two of them. …

On the tenth of January, however, the stars appeared in this position with respect to Jupiter:

East * * O West

that is, there were but two of them, both easterly, the third (as I supposed) being hidden behind Jupiter. As at first, they were in the same straight line with Jupiter and were arranged precisely in the line of the zodiac. Noticing this, and knowing that there was no way in which such alterations could be attributed to Jupiter’s motion, yet being certain that these were still the same stars I had observed (in fact no other was to be found along the line of the zodiac for a long way on either side of Jupiter), my perplexity was now transformed into amazement. I was sure that the apparent changes belonged not to Jupiter but to the observed stars, and I resolved to pursue this investigation with greater care and attention.

And thus, on the eleventh of January, I saw the following disposition:

East * * O West

… I had now decided beyond all question that there existed in the heavens three stars wandering about Jupiter as do Venus and Mercury about the sun, and this became plainer than daylight from observations on similar occasions which followed. Nor were there just three such stars; four wanderers complete their revolutions about Jupiter, and of their alterations as observed more precisely later on we shall give a description here. Also I measured the distances between them by means of the telescope, using the method explained before. Moreover I recorded the times of the observations, especially when more than one was made during the same night–for the revolutions of these planets are so speedily completed that it is usually possible to take even their hourly variations. [Galileo continues to make similar observations until March 2, noting the changes in the "stars" adjacent to Jupiter.] …

Such are the observations concerning the four Medicean planets recently first discovered by me, and although from this data their periods have not yet been reconstructed in numerical form, it is legitimate at least to put in evidence some facts worthy of note. Above all, since they sometimes follow and sometimes precede Jupiter by the same intervals, and they remain within very limited distances either to east or west of Jupiter, accompanying that planet in both its retrograde and direct movements in a constant manner, no one can doubt that they complete their revolutions about Jupiter and at the same time effect all together a twelve-year period about the center of the universe. That they also revolve in unequal circles is manifestly deduced from the fact that at the greatest elongation from Jupiter it is never possible to see two of these planets in conjunction, whereas in the vicinity of Jupiter they are found united two, three, and sometimes all four together. It is also observed that the revolutions are swifter in those planets which describe smaller circles about Jupiter, since the stars closest to Jupiter are usually seen to the east when on the previous day they appeared to the west, and vice versa, while the planet which traces the largest orbit appears upon accurate observation of its returns to have a semimonthly period.

Here we have a fine and elegant argument for quieting the doubts of those who, while accepting with tranquil mind the revolutions of the planets about the sun in the Copernican system, are mightily disturbed to have the moon alone revolve about the earth and accompany it in an annual rotation about the sun. Some have believed that this structure of the universe should be rejected as impossible. But now we have not just one planet rotating about another while both run through a great orbit around the sun; our own eyes show us four stars which wander around Jupiter as does the moon around the earth, while all together trace out a grand revolution about the sun in the space of twelve years. …

Francis Bacon Rejects Superstition and Extols the Virtue of Science

Francis Bacon


The discoveries which have hitherto been made in the sciences are such as lie close to vulgar notions, scarcely beneath the surface. In order to penetrate into the inner and further recesses of nature, it is necessary that both notions and axioms [be] derived from things by a more sure and guarded way, and that a method of intellectual operation be introduced altogether better and more certain. …

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. …

There are and can be only two ways of searching into and discovering truth. The one flies from the senses and particulars to the most general axioms, and from these principles, the truth of which it takes for settled and immovable, proceeds to judgment and the discovery of middle axioms. And this way is now in fashion. The other derives axioms from the senses and particulars, rising by a gradual and unbroken ascent, so that it arrives at the most general axioms last of all. This is the true way, but as yet untried. …

It is not to be forgotten that in every age natural philosophy has had a troublesome adversary and hard to deal with,–namely, superstition and the blind and immoderate zeal of religion. For we see among the Greeks that those who first proposed to man’s uninitiated ears the natural causes for thunder and for storms were thereupon found guilty of impiety. Nor was much more forbearance shown by some of the ancient fathers of the Christian Church to those who, on most convincing grounds (such as no one in his senses would now think of contradicting), maintained that the earth was round and, of consequence, asserted the existence of the antipodes.

Moreover, as things now are, to discourse of nature is made harder and more perilous by the summaries and systems of the schoolmen; who, having reduced theology into regular order as well as they were able, and fashioned it into the shape of an art, ended in incorporating the contentious and thorny philosophy of Aristotle, more than was fit, with the body of religion. …

Lastly, some are weakly afraid lest a deeper search into nature should transgress the permitted limits of sobermindedness; wrongfully wresting and transferring what is said in Holy Writ against those who pry into sacred mysteries to the hidden things of nature, which are barred by no prohibition. Others, with more subtlety, surmise and reflect that if secondary causes are unknown everything can be more readily referred to the divine hand and rod,–a point in which they think religion greatly concerned; which is, in fact, nothing else but to seek to gratify God with a lie. Others fear from past example that movements and changes in philosophy will end in assaults on religion; and others again appear apprehensive that in the investigation of nature something may be found to subvert, or at least shake, the authority of religion, especially with the unlearned.

But these two last fears seem to me to savor utterly of carnal wisdom; as if men in the recesses and secret thoughts of their hearts doubted and distrusted the strength of religion, and the empire of faith over the senses, and therefore feared that the investigation of truth in nature might be dangerous to them. But if the matter be truly considered, natural philosophy is, after the word of God, at once the surest medicine against superstition and the most approved nourishment for faith; and therefore she is rightly given to religion as her most faithful handmaid, since the one displays the will of God, the other his power. …

Descartes’ Discourse on Method Offers a New Method of Reasoning

Rene Descartes


I was then in Germany, attracted thither by the wars in that country, which have not yet been brought to a termination; and as I was returning to the army from the coronation of the Emperor, the setting in of winter arrested me in a locality where, as I found no society to interest me, and was besides fortunately undisturbed by any cares or passions, I remained the whole day in [a stove-heated room,] with full opportunity to occupy my attention with my own thoughts. Of these one of the very first that occurred to me was, that there is seldom so much perfection in works composed of many separate parts, upon which different hands have been employed, as in those completed by a single master. Thus it is observable that the buildings which a single architect has planned and executed, are generally more elegant and commodious than those which several have attempted to improve, by making old walls serve for purposes for which they were not originally built. Thus also, those ancient cities which, from being at first only villages, have become, in course of time, large towns, are usually but ill laid out compared with the regularly constructed towns which a professional architect has freely planned on an open plain; so that although the several buildings of the former may often equal or surpass in beauty those of the latter, yet when one observes their indiscriminate juxtaposition, there a large one and here a small, and the consequent crookedness and irregularity of the streets, one is disposed to allege that chance rather than any human will guided by reason, must have led to such an arrangement. …

It is true … that it is not customary to pull down all the houses of a town with the single design of rebuilding them differently, and thereby rendering the streets more handsome; but it often happens that a private individual takes down his own with the view of erecting it anew, and that people are even sometimes constrained to this when their houses are in danger of falling from age, or when the foundations are insecure. With this before me by way of example, I was persuaded that it would indeed be preposterous for a private individual to think of reforming a state by fundamentally changing it throughout, and overturning it in order to set it up amended; and the same I thought was true of any similar project for reforming the body of the Sciences, or the order of teaching them established in the Schools [scholastic philosophy]: but as for the opinions which up to that time I had embraced, I thought that I could not do better than resolve at once to sweep them wholly away, that I might afterwards be in a position to admit either others more correct, or even perhaps the same when they had undergone the scrutiny of Reason. I firmly believed that in this way I should much better succeed in the conduct of my life, than if I built only upon old foundations, and leant upon principles which, in my youth, I had taken upon trust. …

Among the branches of Philosophy, I had, at an earlier period, given some attention to Logic, and among those of the Mathematics to Geometrical Analysis and Algebra,–three arts or Sciences which ought, as I conceived, to contribute something to my design. But, on examination, I found that, as for Logic, its syllogisms and the majority of its other precepts are of avail rather in the communication of what we already know … than in the investigation of the unknown; and although this Science contains indeed a number of correct and very excellent precepts, there are, nevertheless, so many others, and these either injurious or superfluous, mingled with the former, that it is almost quite as difficult to effect a severance of the true from the false as it is to extract a Diana or a Minerva from a rough block of marble. … By these considerations I was induced to seek some other Method which would comprise [their] advantages … and be exempt from their defects. And as a multitude of laws often only hampers justice, so that a state is best governed when, with few laws, these are rigidly administered; in like manner, instead of the great number of precepts of which Logic is composed, I believed that the four following would prove perfectly sufficient for me, provided I took the firm and unwavering resolution never in a single instance to fail in observing them.

The first was never to accept anything for true which I did not clearly know to be such; that is to say, carefully to avoid precipitancy and prejudice, and to comprise nothing more in my judgment than what was presented to my mind so clearly and distinctly as to exclude all ground of doubt.

The second,to divide each of the difficulties under examination into as many parts as possible, and as might be necessary for its adequate solution.

The third, to conduct my thoughts in such order that, by commencing with objects the simplest and easiest to know, I might ascend by little and little, and, as it were, step by step, to the knowledge of the more complex; assigning in thought a certain order even to those objects which in their own nature do not stand in a relation of antecedence and sequence.

And the last, in every case to make enumerations so complete, and reviews so general, that I might be assured that nothing was omitted.

The long chains of simple and easy reasonings by means of which geometers are accustomed to reach the conclusions of their most difficult demonstrations, had led me to imagine that all things, to the knowledge of which man is competent, are mutually connected in the same way, and that there is nothing so far removed from us as to be beyond our reach, or so hidden that we cannot discover it, provided only we abstain from accepting the false for the true, and always preserve in our thoughts the order necessary for the deduction of one truth from another. …

Pascal’s Famous Wager on God’s Existence

Blaise Pascal


199. Let us imagine a number of men in chains, and all condemned to death, where some are killed each day in the sight of the others, and those who remain see their own fate in that of their fellows, and wait their turn, looking at each other sorrowfully and without hope. It is an image of the condition of men. …

205. When I consider the short duration of my life, swallowed up in the eternity before and after, the little space which I fill, and even can see, engulfed in the infinite immensity of spaces of which I am ignorant, and which know me not, I am frightened, and am astonished at being here rather than there; for there is no reason why here rather than there, why now rather than then. Who has put me here? By whose order and direction have this place and time been allotted to me? Memoria hospitis unius diei praetereuntis.

206. The eternal silence of these infinite spaces frightens me. …

229. This is what I see and what troubles me. I look on all sides, and I see only darkness everywhere. Nature presents to me nothing which is not matter of doubt and concern. If I saw nothing there which revealed a Divinity, I would come to a negative conclusion; if I saw everywhere the signs of a Creator, I would remain peacefully in faith. But, seeing too much to deny and too little to be sure, I am in a state to be pitied; wherefore I have a hundred times wished that if a God maintains nature, she should testify to Him unequivocally, and that, if the signs she gives are deceptive, she should suppress them altogether; that she should say everything or nothing, that I might see which cause I ought to follow. Whereas in my present state, ignorant of what I am or of what I ought to do, I know neither my condition nor my duty. My heart inclines wholly to know where is the true good, in order to follow it; nothing would be too dear to me for eternity.

I envy those whom I see living in the faith with such carelessness, and who make such a bad use of a gift of which it seems to me I would make such a different use.

230. It is incomprehensible that God should exist, and it is incomprehensible that He should not exist; that the soul should be joined to the body, and that we should have no soul; that the world should be created, and that it should not be created, etc.; that original sin should be, and that it should not be. …

346. Thought constitutes the greatness of man.

347. Man is but a reed, the most feeble thing in nature; but he is a thinking reed. The entire universe need not arm itself to crush him. A vapour, a drop of water suffices to kill him. But, if the universe were to crush him, man would still be more noble than that which killed him, because he knows that he dies and the advantage which the universe has over him; the universe knows nothing of this.

All our dignity consists, then, in thought. By it we must elevate ourselves, and not by space and time which we cannot fill. Let us endeavour, then, to think well; this is the principle of morality.

348. A thinking reed.–It is not from space that I must seek my dignity, but from the government of my thought. I shall have no more if I possess worlds. By space the universe encompasses and swallows me up like an atom; by thought I comprehend the world.

… If there is a God, He is infinitely incomprehensible, since, having neither parts nor limits, He has no affinity to us. We are then incapable of knowing either what He is or if He is. This being so, who will dare to undertake the decision of the question? Not we, who have no affinity to Him. …

… But you must wager. It is not optional. You are embarked. Which will you choose then? Let us see. Since you must choose, let us see which interests you least. You have two things to lose, the true and the good; and two things to stake, your reason and your will, your knowledge and your happiness; and your nature has two things to shun, error and misery. Your reason is no more shocked in choosing one rather than the other, since you must of necessity choose. This is one point settled. But your happiness? Let us weigh the gain and the loss in wagering that God is. Let us estimate these two chances. If you gain, you gain all; if you lose, you lose nothing. Wager, then, without hesitation that He is.–”That is very fine. Yes, I must wager; but I may perhaps wager too much.”–Let us see. Since there is equal risk of gain and loss, if you had only to gain two lives, instead of one, you might still wager. But if there were three lives to gain, you would have to play (since you are under the necessity of playing), and you would be imprudent, when you are forced to play, not to chance your life to gain three at a game where there is an equal risk of loss and gain. But there is an eternity of life and happiness. And this being so, if there were an infinity of chances, of which one only would be for you, you would still be right in wagering one to win two, and you would act stupidly, being obliged to play, by refusing to stake one life against three at a game in which out of an infinity of chances there is one for you, if there were an infinity of an infinitely happy life to gain. But there is here an infinity of an infinitely happy life to gain, a chance to gain against a finite number of chances of loss, and what you stake is finite. It is all divided; wherever the infinite is and there is not an infinity of chances of loss against that of gain, there is no time to hesitate, you must give all. And thus, when one is forced to play, he must renounce reason to preserve his life, rather than risk it for infinite gain, as likely to happen as the loss of nothingness.

For it is no use to say it is uncertain if we will gain, and it is certain that we risk, and that the infinite distance between the certainty of what is staked and the uncertainty of what will be gained, equals the finite good which is certainly staked against the uncertain infinite. It is not so, as every player stakes a certainty to gain an uncertainty, and yet he stakes a finite certainty to gain a finite uncertainty, without transgressing against reason. There is not an infinite distance between the certainty staked and the uncertainty of the gain; that is untrue. In truth, there is an infinity between the certainty of gain and the certainty of loss. But the uncertainty of the gain is proportioned to the certainty of the stake according to the proportion of the chances of gain and loss. Hence it comes that, if there are as many risks on one side as on the other, the course is to play even; and then the certainty of the stake is equal to the uncertainty of the gain, so far is it from fact that there is an infinite distance between them. And so our proposition is of infinite force, when there is the finite to stake in a game where there are equal risks of gain and loss, and the infinite to gain. This is demonstrable: and if men are capable of any truths, this is one.

Sir Isaac Newton Lays Down the Ground Rules for the Scientific Method

Isaac Newton


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 an universal property of all bodies whatsoever. That all bodies are movable, and endowed with certain powers (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 argument 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 theirvis insita [force of inertia] 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.

An English Observer Describes the State of Serfdom in Eighteenth-Century Poland

William Coxe


Peasants belonging to individuals are at the absolute disposal of their master, and have scarcely any positive security, either for their properties or their lives. Until 1768 the Statutes of Poland only exacted a fine from a lord who killed his slave; but in that year a decree passed, that the murder of a peasant was a capital crime; yet, as the law in question requires such an accumulation of evidence as is seldom to be obtained, it has more appearance of protection than thereality.

How deplorable must be the state of that country, when a law of that nature was thought requisite to be enacted, yet is found incapable of being enforced. The generality, indeed, of the Polish nobles are not inclined either to establish or give efficacy to any regulations in favour of the peasants, whom they scarcely consider as entitled to the common rights of humanity. A few nobles, however, of benevolent hearts and enlightened understandings, have acted upon different principles, and have ventured upon the expedient of giving liberty to their vassals. The event has showed this project to be no less judicious than humane, no less friendly to their own interests than to the happiness of their peasants: for it appears that in the districts, in which the new arrangement has been introduced, the population of their villages is considerably increased, and the revenues of their estates augmented in a triple proportion.

The first noble who granted freedom to his peasants was [Andrzej] Zamoiski, formerly great chancellor, who in 1760 enfranchised six villages in the palatinate of Masovia. These villages were, in 1777, visited by the author of the Patriotic Letters [advocating political reform], from whom I received the following information: on inspecting the parish-registers of births from 1750 to 1760, that is, during the ten years of slavery immediately preceding their enfranchisement, he found the number of births 434; in the first ten years of their freedom, from 1760 to 1770, 620; and from 1770 to the beginning of 1777, 585 births.

By these extracts it appeared that

During the first period there were only 43 births

second period 62 each year

third period 77

If we suppose an improvement of this sort to take place throughout the kingdom, how great would be the increase of national population!

The revenues of the six villages, since their enfranchisement, have been augmented in a much greater proportion than their population. In their state of vassalage Zamoiski was obliged, according to the custom of Poland, to build cottages and barns for his peasants, and to furnish them with feed, horses, ploughs, and every implement of agriculture; since their attainment of liberty they are become so easy in their circumstances, as to provide themselves with all these necessaries at their own expence; and they likewise cheerfully pay an annual rent, in lieu of the manual labour, which their master formerly exacted from them. By these means the receipts of this particular estate have been nearly tripled.

Voltaire on Religious Toleration



One does not need great art and skilful eloquence to prove that Christians ought to tolerate each other–nay, even to regard all men as brothers. Why, you say, is the Turk, the Chinese, or the Jew my brother? Assuredly; are we not all children of the same father, creatures of the same God?

But these people despise us and treat us as idolaters. Very well; I will tell them that they are quite wrong. It seems to me that I might astonish, at least, the stubborn pride of a Mohammedan or a Buddhist priest if I spoke to them somewhat as follows:

This little globe, which is but a point, travels in space like many other globes; we are lost in the immensity. Man, about five feet high, is certainly a small thing in the universe. One of these imperceptible beings says to some of his neighbours, in Arabia or South Africa: “Listen to me, for the God of all these worlds has enlightened me. There are nine hundred million little ants like us on the earth, but my ant-hole alone is dear to God. All the others are eternally reprobated by him. Mine alone will be happy.”

They would then interrupt me, and ask who was the fool that talked all this nonsense. I should be obliged to tell them that it was themselves. I would then try to appease them, which would be difficult. …

D’Holbach’s System of Nature Offers a New View of the Human Soul

Baron Paul d’Holbach


Man’s ignorance has endured so long, he has taken such slow, irresolute steps to ameliorate his condition, only because he has neglected to study nature, to scrutinize her laws, to search out her resources, to discover her properties. His sluggishness finds its account in permitting himself to be guided by precedent, rather than to follow experience which demands activity; to be led by routine, rather than by his reason which exacts reflection. Hence may be traced the aversion man betrays for everything that swerves from these rules to which he has been accustomed; hence his stupid, his scrupulous respect for antiquity, for the most silly, the most absurd institutions of his fathers; hence those fears that seize him, when the most advantageous changes are proposed to him, or the most probable attempts are made to better his condition. He dreads to examine, because he has been taught to hold it a profanation of something immediately connected with his welfare; he credulously believes the interested advice, and spurns at those who wish to show him the danger of the road he is traveling.

This is the reason why nations linger on in the most scandalous lethargy, groaning under abuses transmitted from century to century, trembling at the very idea of that which alone can remedy their misfortunes. …

The more man reflects, the more he will be convinced that the soul, very far from being distinguished from the body, is only the body itself considered relatively to some of its functions, or to some of the modes of existing or acting of which it is susceptible, whilst it enjoys life. Thus, the soul in man is considered relatively to the faculty he has of feeling, of thinking, and of acting in a mode resulting from his peculiar nature; that is to say, from his properties, from his particular organization, from the modifications, whether durable or transitory, which the beings who act upon him cause his machine to undergo. …

An organized being may be compared to a clock, which, once broken, is no longer suitable to the use for which it was designed. To say that the soul shall feel, shall think, shall enjoy, shall suffer after the death of the body, is to pretend that a clock, shivered into a thousand pieces, will continue to strike the hour and have the faculty of marking the progress of time. Those who say that the soul of man is able to subsist notwithstanding the destruction of the body, evidently support the position that the modification of a body will be enabled to conserve itself after the subject is destroyed; but this is completely absurd.

Rousseau on “Civil Religion”

Jean-Jacques Rousseau


Christianity is a purely spiritual religion, occupied solely with heavenly things; the country of a Christian is not of this world. He does his duty, it is true, but he does it with a profound indifference as to the good or ill success of his efforts. Provided he has nothing to reproach himself with, it matters little to him whether things go well or ill here below. If the state is flourishing, he scarcely dares enjoy the public felicity; he fears to become proud of the glory of his country. If the state degenerates, he blesses the hand of God which lies heavy upon his people. …

Should the depository of this [political] power abuse it, he regards this abuse as the rod with which God punishes his children. People would have scruples about driving out the usurper: it would be necessary to disturb the public repose, to use violence, to shed blood; all this accords ill with the gentleness of the Christian, and, after all, what matters it whether one is a slave or free in this vale of misery? The essential thing is to go to paradise, and resignation is but one more means to accomplish it.

Should some foreign war supervene, the citizens march to combat without difficulty. None among them think of flying; they do their duty, but without passion for victory; they know better how to die than to win. Whether they are victors or vanquished, what matters it? Does not Providence know better than they what they need? …

But I am in error in speaking of a Christian republic; each of these words excludes the other. Christianity preaches only servitude and dependence. Its spirit is too favorable to tyranny not to be taken advantage of by it. Christians are made to be slaves: they know it and do not care; this short life has too little value in their eyes. …

There is, however, a profession of faith purely civil, of which it is the sovereign’s [i.e., the people's] duty to decide upon the articles, not precisely as dogmas of religion, but as sentiments of sociality without which it is impossible to be a good citizen or a faithful subject. Without being able to oblige any one to believe them, the sovereign can banish from the state whoever does not believe them; the sovereign should banish him, not as impious, but as unsocial, as incapable of loving law and justice sincerely, and of sacrificing at need his life to his duty. If any one, having publicly acknowledged these dogmas, conducts himself as if he did not acknowledge them, he should be punished with death; he has committed the greatest of crimes,–he has lied before the law.

The dogmas of civil religion should be simple, few in number, announced with precision, without explanation or commentary. The existence of a powerful, intelligent, benevolent, prescient, and provident Divinity, the life to come, the happiness of the just, the punishment of the wicked, the sacredness of the social contract and the law,–these are the positive dogmas.

As to the negative dogmas, I limit them to one,–intolerance: it enters into the religions which we have excluded. Those who make a distinction between civil intolerance and theological intolerance deceive themselves, to my mind. These two intolerances are inseparable. It is impossible to live in peace with people whom one believes to be damned, to love them is to hate God, who punishes them; they must be redeemed or else tortured. Wherever theological intolerance is admitted, it must have some civil effects; and as soon as it has them the sovereign is no more a sovereign even in temporal matters. From that time priests are the true masters; kings are but their officers.

Montesquieu Identifies the Necessity for the Separation of Governmental Powers

Baron de Montesquieu


In every government there are three sorts of power: the legislative; the executive in respect to things dependent on the law of nations; and the executive in regard to matters that depend on the civil law.

By virtue of the first, the prince or magistrate enacts temporary or perpetual laws, and amends or abrogates those that have been already enacted. By the second, he makes peace or war, sends or receives embassies, establishes the public security, and provides against invasions. By the third, he punishes criminals, or determines the disputes that arise between individuals. The latter we shall call the judiciary power, and the other simply the executive power of the state.

The political liberty of the subject is a tranquillity of mind arising from the opinion each person has of his safety. In order to have this liberty, it is requisite the government be so constituted as one man need not be afraid of another.

When the legislative and executive powers are united in the same person, or in the same body of magistrates, there can be no liberty; because apprehensions may arise, lest the same monarch or senate should enact tyrannical laws, to execute them in a tyrannical manner.

Again, there is no liberty, if the judiciary power be not separated from the legislative and executive. Were it joined with the legislative, the life and liberty of the subject would be exposed to arbitrary control; for the judge would be then the legislator. Were it joined to the executive power, the judge might behave with violence and oppression.

There would be an end of everything, were the same man or the same body, whether of the nobles or of the people, to exercise those three powers, that of enacting laws, that of executing the public resolutions, and of trying the causes of individuals.

Most kingdoms in Europe enjoy a moderate government because the prince who is invested with the two first powers leaves the third to his subjects. In Turkey, where these three powers are united in the Sultan’s person, the subjects groan under the most dreadful oppression.

In the republics of Italy, where these three powers are united, there is less liberty than in our monarchies. Hence their government is obliged to have recourse to as violent methods for its support as even that of the Turks; witness the state inquisitors, and the lion’s mouth into which every informer may at all hours throw his written accusations.

Rousseau Espouses Popular Sovereignty and the General Will

Jean-Jacques Rousseau


Since no man has any natural authority over his fellowmen, and since force is not the source of right, conventions remain as the basis of all lawful authority among men. [Book I, Chapter 4].

Now, as men cannot create any new forces, but only combine and direct those that exist, they have no other means of self-preservation than to form by aggregation a sum of forces which may overcome the resistance, to put them in action by a single motive power, and to make them work in concert.

This sum of forces can be produced only by the combination of many; but the strength and freedom of each man being the chief instruments of his preservation, how can he pledge them without injuring himself, and without neglecting the cares which he owes to himself? This difficulty, applied to my subject, may be expressed in these terms.

“To find a form of association which may defend and protect with the whole force of the community the person and property of every associate, and by means of which each, coalescing with all, may nevertheless obey only himself, and remain as free as before.” Such is the fundamental problem of which the social contract furnishes the solution. …

If then we set aside what is not of the essence of the social contract, we shall find that it is reducible to the following terms: “Each of us puts in common his person and his whole power under the supreme direction of the general will, and in return we receive every member as an indivisible part of the whole.” [Book I, Chapter 6].

But the body politic or sovereign, deriving its existence only from the contract, can never bind itself, even to others, in anything that derogates from the original act, such as alienation of some portion of itself, or submission to another sovereign. To violate the act by which it exists would be to annihilate itself, and what is nothing produces nothing. [Book I, Chapter 7].

It follows from what precedes, that the general will is always right and always tends to the public advantage; but it does not follow that the resolutions of the people have always the same rectitude. Men always desire their own good, but do not always discern it; the people are never corrupted, though often deceived, and it is only then that they seem to will what is evil. [Book II, Chapter 3].

The public force, then, requires a suitable agent to concentrate it and put it in action according to the directions of the general will, to serve as a means of communication between the state and the sovereign, to effect in some manner in the public person what the union of soul and body effects in a man. This is, in the State, the function of government, improperly confounded with the sovereign of which it is only the minister.

What, then, is the government? An intermediate body established between the subjects and the sovereign for their mutual correspondence, charged with the execution of the laws and with the maintenance of liberty both civil and political. [Book III, Chapter 1].

It is not sufficient that the assembled people should have once fixed the constitution of the state by giving their sanction to a body of laws; it is not sufficient that they should have established a perpetual government, or that they should have once for all provided for the election of magistrates. Besides the extraordinary assemblies which unforeseen events may require, it is necessary that there should be fixed and periodical ones which nothing can abolish or prorogue; so that, on the appointed day, the people are rightfully convoked by the law, without needing for that purpose any formal summons. [Book III, Chapter 13].

So soon as the people are lawfully assembled as a sovereign body, the whole jurisdiction of the government ceases, the executive power is suspended, and the person of the meanest citizen is as sacred and inviolable as that of the first magistrate, because where the represented are, there is no longer any representative. [Book III, Chapter 14].

These assemblies, which have as their object the maintenance of the social treaty, ought always to be opened with two propositions, which no one should be able to suppress, and which should pass separately by vote. The first: “Whether it pleases the sovereign to maintain the present form of government.” The second: “Whether it pleases the people to leave the administration to those at present entrusted with it.”

I presuppose here what I believe I have proved, viz., that there is in the State no fundamental law which cannot be revoked, not even this social compact; for if all the citizens assembled in order to break the compact by a solemn agreement, no one can doubt that it could be quite legitimately broken. [Book III, Chapter 18].

An Early English Feminist Denounces the Inequality Inherent in the Institution of Marriage

Mary Astell


Tis true, thro’ Want of Learning, and of that Superior Genius which Men as Men lay claim to, she was ignorant of the Natural Inferiority of our Sex, which our Masters lay down as a Self-Evident and Fundamental Truth. She saw nothing in the Reason of Things, to make this either a Principle or a Conclusion, but much to the contrary. …

That the Custom of the World has put Women, generally speaking, into a State of Subjection, is not deny’d; but the Right can no more be prov’d from the Fact, than the Predominancy of Vice can justifie it. …

The Domestic Sovereign [husband] is without Dispute Elected, and the Stipulations and Contract are mutual, is it not then partial in Men to the last degree, to contend for, and practise that Arbitrary Dominion in their Families, which they abhor and exclaim against in the State? For if Arbitrary Power is evil in itself, and an improper Method of Governing Rational and Free Agents, it ought not to be Practis’d any where; Nor is it less, but rather more mischievous in Families than in Kingdoms, by how much 100000 Tyrants are worse than one.

Joseph II, Religious Toleration, and the Austrian Jews

Joseph II


In order to make the Jews more useful, the discrimination hitherto observed in relation to their clothing is abolished in its entirety. Consequently the obligation for the men to wear yellow armbands and the women to wear yellow ribbons is abolished. If they behave quietly and decently, then no one has the right to dictate to them on matters of dress.

Within two years the Jews must abandon their own language. … Consequently the Jews may use their own language only during religious services.

Those Jews who do not have the opportunity to send their children to Jewish schools are to be compelled to send them to Christian schools, to learn reading, writing, arithmetic and other subjects.

Jewish youth will also be allowed to attend the imperial universities.

To prevent the Jewish children and the Jews in general suffering as a result of the concessions granted to them, the authorities and the leaders of the local communities must instruct the subjects in a rational manner that the Jews are to be regarded like any other fellow human-beings and that there must be an end to the prejudice and contempt which some subjects, particularly the unintelligent, have shown towards the Jewish nation and which several times in the past have led to deplorable behaviour and even criminal excesses. On the other hand the Jews must be warned to behave like decent citizens and it must be emphasised in particular that they must not allow the beneficence of His Majesty to go to their heads and indulge in wanton and licentious excesses and swindling.

Catherine the Great’s Grand Instruction to the Legislative Commission

Catherine the Great


6. Russia is a European state.

7. This is clearly demonstrated by the following observations: the alterations which Peter the Great undertook in Russia succeeded with greater ease because the manners which prevailed at that time, and had been introduced amongst us by a mixture of different nations and the conquest of foreign territories, were quite unsuitable to the climate. Peter the First, by introducing the manners and customs of Europe among the Europeanpeople in his domains, found at that time such means [success] as even he himself did not expect. …

9. The Sovereign is absolute; for there is no other authority but that which centers in his single person that can act with a vigor proportionate to the extent of such a vast Dominion. …

13. What is the true end of Monarchy? Not to deprive people of their natural liberty but to correct their actions, in order to attain the Supreme Good. …

15. The intention and end of Monarchy is the glory of the Citizens, of the State, and of the Sovereign. …

66. All laws which aim at the extremity of rigor, may be evaded. It is moderation which rules a people, and not excess of severity.

67. Civil liberty flourishes when the laws deduce every punishment from the peculiar nature of every crime. The application of punishment ought not to proceed from the arbitrary will or mere caprice of the Legislator, but from the nature of the crime. …

68. Crimes are divisible into four classes: against religion, against manners [morality], against the peace, against the security of the citizens. …

74. I include under the first class of crimes [only] a direct and immediate attack upon religion, such as sacrilege, distinctly and clearly defined by law. … In order that the punishment for the crime of sacrilege might flow from the nature of the thing, it ought to consist in depriving the offender of those benefits to which we are entitled by religion; for instance, by expulsion from the churches, exclusion from the society of the faithful for a limited time, or for ever. …

76. In the second class of crimes are included those which are contrary to good manners.

77. Such [include] the corruption of the purity of morals in general, either publick or private; that is, every procedure contrary to the rules which show in what manner we ought to enjoy the external conveniences given to man by Nature for his necessities, interest, and satisfaction. The punishments of these crimes ought to flow also from the nature of the thing [offense]: deprivation of those advantages which Society has attached to purity of morals, [for example], monetary penalties, shame, or dishonor … expulsion from the city and the community; in a word, all the punishments which at judicial discretion are sufficient to repress the presumption and disorderly behavior of both sexes. In fact, these offenses do not spring so much from badness of heart as from a certain forgetfulness or mean opinion of one’s self. To this class belong only the crimes which are prejudicial to manners, and not those which at the same time violate publick security, such as carrying off by force and rape; for these are crimes of the fourth class.

78. The crimes of the third class are those which violate the peace and tranquillity of the citizens. The punishments for them ought also to flow from the very nature of the crime, as for instance, imprisonment, banishment, corrections, and the like which reclaim these turbulent people and bring them back to the established order. Crimes against the peace I confine to those things only which consist in a simple breach of the civil polity.

79. The penalties due to crimes of the fourth class are peculiarly and emphatically termed Capital Punishments. They are a kind of retaliation by which Society deprives that citizen of his security who has deprived, or would deprive, another of it. The punishment is taken from the nature of the thing, deduced from Reason, and the sources of Good and Evil. Acitizen deserves death when he has violated the publick security so far as to have taken away, or attempted to take away, the life of another. Capital punishment is the remedy for a distempered society. If publick security is violated with respect to property, reasons may be produced to prove that the offender ought not in such a case suffer capital punishment; but that it seems better and more conformable to Nature that crimes against the publick security with respect to property should be punished by deprivation of property. And this ought inevitably to have been done, if the wealth of everyone had been common, or equal. But as those who have no property are always most ready to invade the property of others, to remedy this defect corporal punishment was obliged to be substituted for pecuniary. What I have here mentioned is drawn from the nature of things, and conduces to the protection of the liberty of the citizens. …

348. The rules of Education are the fundamental institutes which train us up to be citizens. …

350. It is impossible to give a general education to a very numerous people and to bring up all the children in schools; for that reason, it will be proper to establish some general rules which may serve by way of advice to all parents.

351. Every parent is obliged to teach his children the fear of God as the beginning of all Wisdom, and to inculcate in them all those duties which God demands from us in the Ten Commandments and in the rules and traditions of our Orthodox Eastern Greek religion.

352. Also to inculcate in them the love of their Country, and to ensure they pay due respect to the established civil laws, and reverence the courts of judicature in their Country as those who, by the appointment of God, watch over their happiness in this world.

353. Every parent ought to refrain in the presence of his children not only from actions but even from words that tend to injustice and violence, as for instance, quarreling, swearing, fighting, every sort of cruelty, and such like behavior; and not to allow those who are around his children to set them such bad examples. …

511. A Monarchy is destroyed when a Sovereign imagines that he displays his power more by changing the order of things than by adhering to it, and when he is more fond of his own imaginations than of his will, from which the laws proceed and have proceeded.

512. It is true there are cases where Power ought and can exert its full influence without any danger to the State. But there are cases also where it ought to act according to the limits prescribed by itself.

513. The supreme art of governing a State consists in the precise knowledge of that degree of power, whether great or small, which ought to be exerted according to the different exigencies of affairs. For in a Monarchy the prosperity of the State depends, in part, on a mild and condescending government. …

522. Nothing more remains now for the Commission to do but to compare every part of the laws with the rules of this Instruction.

Mr. Cowherd