they assume causes, and principles before established, as if they were certain truths, and argue from them. Nothing can be more absurd than these proceedings. It is agreed, I think, out of the schools at least, that Aristotle was eminently guilty of them; for he dealt more in common notions, than experiments, and built a world with categories, that is, by a certain logical arrangement of words: and yet even Aristotle seems to have warned philosophers against this abuse; for he taught, according to the report of Sextus Empiricus, that they should not neglect sense and seek for reasons, "posthabito sensu quærere rationem;" that is, that they should not carry speculation further than experiment and observation authorise it first, and confirm it afterwards. The principal reasons of a contrary conduct may be found in laziness, and vanity; in the first sometimes, in the other always. Philosophers have found it more easy, and more compendious to imagine, than to discover; to guess, than to know. They have taken, therefore, this way to fame, which has been their object, at least, as much as truth: and many a wild hypothesis has passed for a real system.

Strato was a famous philosopher, the scholar of Theophrastus, and the master of Ptolemy Philadelphus. As little, and as ill as we are informed of the state of natural philosophy among the more ancient naturalists of Greece, such as Pythagoras, Anaxagoras, Democritus, and others, whose names are preserved though their works are lost, we know enough of Plato and Aristotle, whose works have been preserved, perhaps more to the detriment than to the advancement of learning, to determine what the state of it was in the days of Strato. We know that it was no longer the study of nature by observation, and experiment; but that it consisted in a jargon of words, or at best in some vague hypothetical reasonings: and yet Strato, who could not have told the Egyptian king how the idea of purple, the color of his robe, was produced, pretended to account for all the phenomena, and among other doctrines, to establish that of the plenum, for he laughed at the vacuum, as well as at the whole atomical system of Democritus.

Hypotheses are much in the favor of some philosophers; for there have been many Stratos even among the moderns. But hypotheses may be employed without being abused. In all our attempts to account for the phenomena of nature, there will be something hypothetical necessarily included. The analytic method itself, our surest road to science, does not conduct us further than extreme probability, as it has been observed; and this probability must stand us in lieu of certainty. But when we cannot arrive by this method at such a probability, is it reasonable to make an hypothesis? Is it reasonable, when we

cannot draw from observation and experiment, such conclusions as may be safe foundations on which to proceed by the synthetic method in the pursuit of truth, to assume certain principles, as if they were founded in the analytic method, which have been never proved, nor perhaps suggested by the phenomena, in hopes that they may be so afterwards? In a word, when the only clue we have fails us; which is most reasonable, to stop short, or to push forwards without any clue at all into the labyrinth of nature? I make no scruple of deciding in a case, so plain, that it would be a silly affectation of modesty, not modesty, to hesitate. When the phenomena do not point out to us any sufficient reason why, and how a thing is as we discover it to be, nor the efficient cause of it, there is a sufficient reason for stopping short, and confessing our ignorance; but none for seeking, out of the phenomena, this reason, and this cause which we cannot find in them. This is learned ignorance, of which the greatest philosophers have no reason to be ashamed. "Rationem-harum gravitatis proprietatum ex phænomenis nondum potui deducere, et 'hypotheses non fingo," said our Newton, after having advanced natural knowledge far beyond his cotemporaries, on the sure foundations of experiment, and geometry. How preferable is this learned ignorance to that ignorant learning, of which so many others have foolishly boasted? Des Cartes, who mingled so much hypothetical with so much real knowledge, boasted in a letter to his intimate friend the minime Mersenne, "that he should think he knew nothing in natural philosophy, if he was only able to say how things may be, without demonstrating that they cannot be otherwise." Leibnitz, who dealt in little else than hypotheses, speaking, in his reply to Bayle's reflections on his pre-established harmony, of the ridiculous whimsy of his Monades, and the rest of his metaphysical trash, compares himself to Antæus; asserts that "every objection gives him new strength," and boasts vainly, that he might say without vanity, ❝omnia præcepi, atque animo mecum ante peregi."

It will be urged, perhaps, as decisive in favor of hypotheses, that they may be of service, and can be of no disservice to us, in our pursuit of knowledge. A hypothesis founded on mere arbitrary assumptions will be a true hypothesis, and therefore of service to philosophy, if it is confirmed by many observations afterwards, and if no one phenomenon stand in opposition to it. A hypothesis that appears inconsistent with the phenomena will be soon demonstrated false, and as soon rejected. This reasoning, which is the sum of all that can be said for them, will not hold good, I think, in either case, enough to countenance the abuse of them, which is made by the very persons who urge this plea in favor of them. That such a hypothesis may be true,

is within the bounds of possibility; because it implies no contradiction to suppose that men, who pass their lives in guessing, may guess sometimes right. A man may throw ten sixes with ten dice; but no man in his senses would lay that he did, nor venture his stake on such a chance. In the other case, it is true that a hypothesis inconsistent with the phenomena may be soon demonstrated false. But it is not true that it will be as soon rejected. If philosophers are fond of making hypotheses, their disciples are as zealous to defend them. The honor of a whole sect is thought to be engaged, and every individual is piqued that another should show that to be false, which he has all his life taken to be true; so that notwithstanding all the graces of novelty, a new truth will have much to do to dislodge an old error. Instances of this sort are innumerable. Let us produce one from astronomy itself.

If any hypothesis was ever assumed with a plausible probability, that which we call the Ptolemaic was so. The apparent face of the heavens led men to it. We may say that the phenomena suggested it, and that the revolution of the sun, planets, and stars, in several spheres round the earth, could scarcely be doubted of by men who assumed any general conclusions, instead of drawing them all from a long course of particular observations carefully and learnedly made. The plausibility of this false hypothesis, and the authority of the peripatetic school established it on the ruins of the true system which Pythagoras had brought long before into Italy from the east, and which was probably that of the Egyptian and Chaldean astronomers. False as it was, it maintained its credit thirteen or fourteen centuries, if we reckon only from the time of the Alexandrian astronomer Ptolemy to that of Copernicus. Many difficulties had occurred, but as fast as they did so, new assumptions were made to reconcile them, till the whole became one complicated heap of hypothesis upon hypothesis. It was banished at last, and a truer system took its place. The fauters of hypotheses would have us believe, that even the detection of their falsehood gives occasion to our improvement in knowledge. But the road to truth does not lie through the precincts of error, and the improvement of astronomy was not owing to the destruction of the Ptolemaic hypothesis; but the destruction of this hypothesis was owing to the improvement of astronomy. If this hypothesis had never been made, Copernicus would not have had the honor of reviving the Pythagorean system, but mankind would have had the benefit of pursuing, without interruption, a system founded on knowledge, instead of pursuing, during an interval of so many centu. ries, a hypothesis founded on assumption.

To this ancient, let us join a modern instance to suggest the

same reflections, and confirm the same proofs. The system of Des Cartes dazzled and imposed at first. It was soon attacked, however, but it has not been so soon defeated. No man, perhaps, was ever so fit, as this philosopher, to make and maintain a hypothesis; to assume, and to improve and defend his assumpThe notion he entertained and propagated, that there is, besides clear ideas, a kind of inward sentiment of evidence, which may be a principle of knowledge, is, I suppose, dangerous in physical inquiries as well as in abstract reasoning. He who departs from the analytic method, to establish general propositions concerning the phenomena on assumptions, and who reasons from these assumptions, afterwards, on inward sentiments of evidence, as they are called, instead of clear and real ideas, lays aside, at once, the only sure guides to knowledge. No wonder then if he wanders from it. This Des Cartes did very widely in his construction of a world, and yet by dint of genius he gave a great air of simplicity and plausibility to his hypothesis, and he knew how to make even geometry subservient to error. It proved in other hands, indeed, the instrument of detecting his errors, and of establishing truer principles of natural philosophy. He furnished to others arms against himself, among the rest to our Newton; for though the system of the latter be no more owing to the hypothesis of the former, than that of Copernicus to that of Ptolemy, yet was it the application of geometry to physics, that enabled the British philosopher to make so many admirable discoveries: and the introduction of geometry into physics must be acknowledged due to the French philosopher. To conclude, by bringing this example to our purpose. The plenum of Des Cartes is well nigh destroyed; many of his laws of motion are shown to be false; the mills that served to grind his three elements are demolished: and his fluid matter in which, as in a torrent, the planets were carried round the sun, whilst a similar motion in the particular vortex of every planet impelled all bodies to the centre, is vanished. Notwithstanding all this, how slowly, how unwillingly have many philosophers departed from the Cartesian hypothesis? They have had recourse to the most forced suppositions to defend it; and when it has been demonstrated false in one of the principal parts, in that of his fluid matter, whose rapid circulation he supposes to cause the fall of bodies, and the motion of the planets, and which he invented to explain these phenomena, we shall be told very gravely, that some fluid matter or other may, however, in some manner or other, be the cause of these phenomena. It is even ridiculous to observe the same men tenacious of a hypothesis neither deduced from the phenomena, nor consistent with them, and averse to receive, or at best extremely scrupulous about receiving, a sys

tem built on observation and experiment, not on assumption, and which all the phenomena conspire to establish.

If philosophers meant nothing more than the discovery of truth, they would confine themselves to those rules by which alone, and to those bounds of inquiry within which alone, we are able to discover it. But a predominant principle of vanity makes them break these rules, and pass these bounds. Not content with philosophical liberty, they affect to proceed licentiously: and it is this affectation that makes them so fond of hypotheses, by the means of which, how imperfect soever their knowledge is, their pretended systems are still complete. Thus it has happened that natural philosophers have filled their works with fictions, and, like lying travellers, have given descriptions of countries through which they never passed. They have done even more, they have affected to reveal the secrets of courts they never saw. This I mean; they have not only supposed existences that never existed, but have presumed themselves able to give a sufficient reason for every thing that does exist. Leibnitz, who had much knowledge and some sagacity, but too much pretended subtilty and real presumption, imposed this obligation on philosophers, the obligation of adulterating physics with metaphysics. Thus for instance, he thought himself obliged to give a sufficient reason how, and why the extension of body, or body according to the Cartesians, becomes possible; for though actuality may, he denied that possibility could, proceed from the will of God. He found this reason neither in sensible extension, nor in the insensible atoms that compose body. But he found it happily in his Monades, that is in simple, unextended beings, that are the only substances, and that compose all extension, which God could not have created if he had not created them first. Is it worth while to acquire the name of a great philosopher, at the expense of amusing mankind with such hypothetical extravagances? Surely not.

Since I have ventured to censure Des Cartes on this head, on which he was very liable to censure, I think myself obliged to justify him on another, on which he has been accused very unjustly. Strato might be an atheist, for what I know, though mention is made, in the catalogue of his works preserved by Diogenes Laertius, of three books that he wrote concerning the gods. But the passage in the academics of Tully, where it is said, that he did not employ the gods in making the world "negat operâ deorum se uti ad fabricandum mundum," will not persuade me that he was so. Nothing can be more consistent than to acknowledge a Supreme Being, the source of all existence, the first efficient cause of all things, and to account for the phenomena by physical and mechanical causes, by matter and motion.