CHAPTER III.

OF HYPOTHESES.

EVERY branch of human knowledge hath its proper principles, its proper foundation and method of reasoning; and, if we endeavour to build it upon any other foundation, it will never stand firm and stable. Thus the historian builds upon testimony, and rarely indulges conjecture. The antiquarian mixes conjecture with testimony; and the former often makes the larger ingredient. The mathematician pays not the least regard either to testimony or conjecture, but deduces every thing, by demonstrative reasoning, from his definitions and axioms. Indeed, whatever is built upon conjecture, is improperly called science; for conjecture may beget opinion, but cannot produce knowledge. Natural philosophy must be built upon the phenomena of the material system, discovered by observation and experiment.

When men first began to philosophize, that is, to carry their thoughts beyond the objects of sense, and to inquire into the causes of things, and the secret operations of nature, it was very natural for them to indulge "jecture; nor was it to be expected, that, in many ages, they should over the proper and scientific way of proceeding in philosophical disquisitions. Accordingly we find, that the most ancient systems in every branch of philosophy were nothing but the conjectures of men famous for their wisdom, whose fame gave authority to their opinions. Thus, in early ages, wise men conjectured, that this earth is a vast plain surrounded on all hands by a boundless ocean: That from this ocean, the sun, moon, and stars emerge at their rising, and plunge into it again at their setting.

With regard to the mind, men in their rudest state are apt to conjecture that the principle of life in a man is his breath; because the most obvious distinction between a living and a dead man is, that the one breathes and the other does not. To this it is owing that, in ancient languages, the word which denotes the soul, is that which properly signifies breath or air.

As men advance in knowledge, their first conjectures appear silly and childish, and give place to others, which tally better with later observations and discoveries. Thus, one system of philosophy succeeds another, without any claim to superior merit but this, that it is a more ingenious system of conjectures, and accounts better for common appearances.

To omit many ancient systems of this kind, Des Cartes, about the middle of the last century, dissatisfied with the materia prima, the substantial forms, and the occult qualities of the peripatetics, conjectured boldly, that the heavenly bodies of our system are carried round by a vortex or whirlpool of subtile matter, just as straws and chaff are carried round in a tub of water. He conjectured, that the soul is seated in a small gland in the brain, called the pineal gland: That there, as in her chamber of presence, she receives intelligence of every thing that affects the senses, by means of a subtile fluid contained in the nerves, called the animal spirits; and that she despatches these animal spirits as her messengers, to put in motion the several muscles of the body, as there is occasion. By such conjectures as these, Des Cartes could account for every phenomenon in nature, in such a plausible manner as gave satisfaction to a great part of the learned world for more than half a century.

Such conjectures in philosophical matters have commonly got the name of hypotheses or theories. And the invention of an hypothesis, founded on

some slight probabilities, which accounts for many appearances of nature, has been considered as the highest attainment of a philosopher. If the hypothesis hangs well together, is embellished by a lively imagination, and serves to account for common appearances, it is considered by many as having all the qualities that should recommend it to our belief; and all that ought to be required in a philosophical system.

There is such proneness in men of genius to invent hypotheses, and in others to acquiesce in them as the utmost which the human faculties can attain in philosophy, that it is of the last consequence to the progress of real knowledge, that men should have a clear and distinct understanding of the nature of hypotheses in philosophy, and of the regard that is due to them.

Although some conjectures may have a considerable degree of probability, yet it is evidently in the nature of conjecture to be uncertain. In every case, the assent ought to be proportioned to the evidence; for to believe firmly what has but a small degree of probability, is a manifest abuse of our understanding. Now, though we may, in many cases, form very probable conjectures concerning the works of men, every conjecture we can form with regard to the works of God has as little probability as the conjectures of a child with regard to the works of a man.

The wisdom of God exceeds that of the wisest man, more than his wisdom exceeds that of a child. If a child were to conjecture how an army is to be formed in the day of battle; how a city is to be fortified, or a state governed; what chance has he to guess right? As little chance has the wisest man when he pretends to conjecture how the planets move in their courses, how the sea ebbs and flows, and how our minds act upon our bodies.

If a thousand of the greatest wits that ever the world produced, were, without any previous knowledge in anatomy, to sit down and contrive how, and by what internal organs, the various functions of the human body are carried on; how the blood is made to circulate, and the limbs to move, they would not in a thousand years hit upon any thing like the truth.

Of all the discoveries that have been made concerning the inward structure of the human body, never one was made by conjecture. Accurate observations of anatomists have brought to light innumerable artifices of nature in the contrivance of this machine of the human body, which we cannot but admire as excellently adapted to their several purposes. But the most sagacious physiologist never dreamed of them till they were discovered. On the other hand, innumerable conjectures, formed in different ages, with regard to the structure of the body, have been confuted by observation, and none ever confirmed.

What we have said of the internal structure of the human body, may be said, with justice, of every other part of the works of God, wherein any real discovery has been made. Such discoveries have always been made by patient observation, by accurate experiments, or by conclusions drawn by strict reasoning from observations and experiments; and such discoveries have always tended to refute, but not to confirm, the theories and hypotheses which ingenious men had invented.

As this is a fact confirmed by the history of philosophy in all past ages, it ought to have taught men long ago to treat with just contempt hypotheses in every branch of philosophy, and to despair of ever advancing real knowledge in that way. The Indian philosopher, being at a loss to know how the earth was supported, invented the hypothesis of a huge elephant; and this elephant he supposed to stand upon the back of a huge tortoise.

This hypothesis, however ridiculous it appears to us, might seem very reasonable to other Indians, who knew no more than the inventor of it; and the same will be the fate of all hypotheses invented by men to account for the works of God: They may have a decent and plausible appearance to those who are not more knowing than the inventor; but, when men come to be more enlightened, they will always appear ridiculous and

childish.

This has been the case with regard to hypotheses that have been revered by the most enlightened part of mankind for hundreds of years; and it will always be the case to the end of the world. For, until the wisdom of men bear some proportion to the wisdom of God, their attempts to find out the structure of his works by the force of their wit and genius, will be

vain.

The finest productions of human art are immensely short of the meanest works of nature. The nicest artist cannot make a feather, or the leaf of a tree. Human workmanship will never bear a comparison with divine. Conjectures and hypotheses are the invention and the workmanship of men, and must bear proportion to the capacity and skill of the inventor; and therefore will always be very unlike to the works of God, which it is the business of philosophy to discover.

The world has been so long befooled by hypotheses in all parts of philosophy, that it is of the utmost consequence to every man, who would make any progress in real knowledge, to treat them with just contempt, as the reveries of vain and fanciful men, whose pride makes them conceive themselves able to unfold the mysteries of nature by the force of their genius. A learned man, in an epistle to Des Cartes, has the following observation, which very much deserved the attention of that philosopher, and of all that come after him: "When men, sitting in their closet, and consulting only their books, attempt disquisitions into nature, they may indeed tell how they would have made the world, if God had given them that in commission: that is, they may describe chimeras, which correspond with the imbecility of their own minds, no less than the admirable beauty of the universe corresponds with the infinite perfection of its Creator; but without an understanding truly divine, they can never form such an idea to themselves as the Deity had in creating things."

Let us, therefore, lay down this as a fundamental principle in our inquiries into the structure of the mind and its operations, that no regard is due to the conjectures or hypotheses of philosophers, however ancient, however generally received. Let us accustom ourselves to try every opinion by the touchstone of fact and experience. What can fairly be deduced from facts duly observed, or sufficiently attested, is genuine and pure; it is the voice of God, and no fiction of human imagination.

The first rule of philosophizing laid down by the great Newton, is this; Causas rerum naturalium, non plures admitti debere, quam quæ et veræ sint, et earum phænomenis explicandis sufficiant. "No more causes, nor any other causes of natural effects ought to be admitted, but such as are both true, and are sufficient for explaining their appearances." This is a golden rule; it is the true and proper test, by which what is sound and solid in philosophy may be distinguished from what is hollow and vain.

If a philosopher, therefore, pretend to show us the cause of any natural effect, whether relating to matter or to mind; let us first consider whether there is sufficient evidence that the cause he assigns does really exist. If there is not, reject it with disdain as a fiction which ought to have no place in genuine philosophy. If the cause assigned really exist, consider

in the next place whether the effect it is brought to explain necessarily follows from it. Unless it hath these two conditions, it is good for nothing. When Newton had shown the admirable effects of gravitation in our planetary system, he must have felt a strong desire to know its cause. He could have invented an hypothesis for this purpose, as many had done before him. But his philosophy was of another complexion. Let us hear what he says: Rationem harum gravitatis proprietatum ex phænomenis non potui deducere, et hypotheses non fingo. Quicquid enim ex phænomenis non deducitur hypothesis vocanda est. Et hypotheses, seu metaphysicæ, seu physicæ, seu qualitatum occultarum, seu mechanicæ, in philosophia experimentali locum non habent.

CHAPTER IV.

OF ANALOGY.

It is natural to men to judge of things less known, by some similitude they observe, or think they observe, between them and things more familiar or better known. In many cases, we have no better way of judging. And where the things compared have really a great similitude in their nature, when there is reason to think that they are subject to the same laws, there may be a considerable degree of probability in conclusions drawn from analogy.

Thus, we may observe a very great similitude between this earth which we inhabit, and the other planets, Saturn, Jupiter, Mars, Venus, and Mercury. They all revolve round the sun, as the earth does, although at different distances, and in different periods. They borrow all their light from the sun, as the earth does. Several of them are known to revolve round their axis like the earth, and, by that means, must have a like succession of day and night. Some of them have moons, that serve to give them light in the absence of the sun, as our moon does to us. They are all, in their motions, subject to the same law of gravitation, as the earth is. From all this similitude, it is not unreasonable to think, that those planets may, like our earth, be the habitation of various orders of living creatures. There is some probability in this conclusion from analogy.

In medicine, Physicians must, for the most part, be directed in their prescriptions by analogy. The constitution of one human body is so like to that of another, that it is reasonable to think, that what is the cause of health or sickness to one, may have the same effect upon another. And this generally is found true, though not without some exceptions.

In politics, we reason, for the most part, from analogy. The constitution of human nature is so similar in different societies or commonwealths, that the causes of peace and war, of tranquillity and sedition, of riches and poverty, of improvement and degeneracy, are much the same in all.

Analogical reasoning, therefore, is not, in all cases, to be rejected. It may afford a greater or a less degree of probability, according as the things compared are more or less similar in their nature. But it ought to be observed, that, as this kind of reasoning can afford only probable evidence at best; so, unless great caution be used, we are apt to be led into error by it. For men are naturally disposed to conceive a greater similitude in things than there really is."

To give an instance of this: Anatomists, in ancient ages, seldom dissected human bodies; but very often the bodies of those quadrupeds, whose in

ternal structure was thought to approach nearest to that of the human body. Modern Anatomists have discovered many mistakes the ancients were led into, by their conceiving a greater similitude between the structure of men and of some beasts, than there is in reality. By this, and many other instances that might be given, it appears, that conclusions built on analogy stand on a slippery foundation; and that we ought never to rest upon evidence of this kind, when we can have more direct evidence.

I know no author who has made a more just and a more happy use of this mode of reasoning, than Bishop Butler, in his Analogy of Religion, Natural and Revealed, to the Constitution and Course of Nature. In that excellent work, the author does not ground any of the truths of religion upon analogy, as their proper evidence. He only makes use of analogy to answer objections against them. When objections are made against the truths of religion which may be made with equal strength against what we know to be true in the course of nature, such objections can have no weight.

Analogical reasoning, therefore, may be of excellent use in answering objections against truths which have other evidence. It may likewise give a greater or a less degree of probability in cases where we can find no other evidence. But all arguments, drawn from analogy, are still the weaker, the greater disparity there is between the things compared; and therefore must be weakest of all when we compare body with mind, because there are no two things in nature more unlike.

There is no subject in which men have always been so prone to form their notions by analogies of this kind, as in what relates to the mind. We form an early acquaintance with material things by means of our senses, and are bred up in a constant familiarity with them. Hence we are apt to measure all things by them; and to ascribe to things most remote from matter, the qualities that belong to material things. It is for this reason, that mankind have, in all ages, been so prone to conceive the mind itself to be some subtile kind of matter; that they have been disposed to ascribe human figure and human organs, not only to angels, but even to the Deity. Though we are conscious of the operations of our own minds when they are exerted, and are capable of attending to them, so as to form a distinct notion of them; this is so difficult a work to men, whose attention is constantly solicited by external objects, that we give them names from things that are familiar, and which are conceived to have some similitude to them; and the notions we form of them are no less analogical than the names we give them. Almost all the words by which we express the operations of the mind, are borrowed from material objects. To understand. to conceive, to imagine, to comprehend, to deliberate, to infer, and many others, are words of this kind; so that the very language of mankind, with regard to the operations of our minds, is analogical. Because bodies are affected only by contact and pressure, we are apt to conceive, that what is an immediate object of thought, and affects the mind, must be in contact with it, and make some impression upon it. When we imagine any thing, the very word leads us to think, that there must be some image in the mind of the thing conceived. It is evident, that these notions are drawn from some similitude conceived between body and mind, and between the properties of body and the operations of mind,

To illustrate more fully that analogical reasoning from a supposed similitude of mind to body, which I conceive to be the most fruitful source of error with regard to the operations of our minds, I shall give an instance of it.