61. Though it may be impossible to collect the opinions of all men upon all points, there are many cases in which it is otherwise; so that the foregoing postulate will still hold good.

Obs. Who can doubt, for instance, whether mankind have, in all ages, believed the existence of a material world, and that those things which we see and handle, are real and not mere illusions and apparitions? Who can doubt whether mankind have universally believed that very thing that begins to exist, must have a cause? Who can doubt, whether mankind have been universally persuaded that there is a right and a wrong in human conduct? Some things, which in certain circumstance, they ought to do, and other things which they ought not to do?

Corol. The universality of these opinions, and of many such that might be named, is sufficiently evident, from the whole tenor of men's conduct, as far as our acquaintance reaches, and from the records of historians of all nations, transmitted to us from the remotest ages.

62. There are other opinions that appear to be universal, from what is common in the structure of all languages, ancient and modern, polished and barbarous. Language is the express image and picture of human thoughts; and from the picture, we may often draw certain conclusions with regard to the original.

Illus. 1. We find in all languages the same parts of speech, noun, substantive and adjective; verbs active and passive, varied according to the tenses of past, present, and future; we find adverbs, prepositions, and conjunctions. There are general rules of syntax common to all languages. This uniformity in the structure of language, shews a certain degree of uniformity in those notions upon which the structure of language is founded.

2. We find in the structure of all languages, the distinction of acting and being acted upon, the distinction of action and agent, of quality and subject, and many others of the like kind; which shews that these distinctions are founded in the universal sense of mankind.

Corol. There are many occasions on which it is necessary to argue from the sense of mankind expressed in the structure of language; and therefore it was proper at the threshold to take notice of the force of arguments drawn from this topic.

63. We shall also take for granted, as first principles, such facts as are attested to the conviction of all sober men, either by their senses, by memory, or by human testimony.

Obs. 1. For, though scepticism may endeavour to discredit the testimony of the senses, we never heard of any sceptic who struck his head against a post, or stept into a kennel because he did not believe his eyes.

2. Let us, however, be cautious, that we do not adopt opinions

as first principles, which are not entitled to that character. Let us deal with every thing offered as a first principle, as an upright judge does with a witness who has a fair character. He pays a regard to the testimony of such witness, while his character is unimpeached; but if it can be shewn that he is suborned, or that he is influenced by malice or partial favour, his testimony loses all credit, and is justly rejected.

CHAPTER III.

OF HYPOTHESES.

64. EVERY branch of human knowledge hath its proper principles, its proper foundation and method of reasoning; and if we endeavour to build upon any other foundation, the fabric we raise will never stand firm.

Illus. 1. Thus, the historian builds upon testimony, and rarely indulges conjecture.

2. The antiquary mixes conjecture with testimony; and the former often makes the larger ingredient.

3. The mathematician pays not the least regard either to testimony or conjecture, but deduces every thing, by demonstrative reasoning, from his definitions and axioms.

Corol. Whatever, therefore, is built upon conjecture, is improperly called science; for though conjecture may beget opinion, it cannot produce knowledge. Natural philosophy must be built upon the laws of the material system, discovered by observation and experiment.

65. When men began to philosophize, or to carry their thoughts beyond the objects of sense, and to inquire into the causes of things, their ignorance of a scientific way of proceeding in such philosophical disquisitions, gave birth to conjecture.

Illus. 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 opin

ions.

Example. Thus, in early ages, wise men conjectured that the earth was a vast plain, surrounded on all sides by a boundless ocean; that from this ocean, the sun, moon, and stars, emerged at their rising, and plunged into it again at their setting.

66. With regard to the mind, men in their rudest state are apt to conjecture that the principle of life in man is his breath; because the most obvious distinction between a liv

ing and a dead man is, that the one breathes, and the other does not.

Obs. To this it is owing that, in ancient languages, the word which denotes the soul, is that which properly signifies breath, or air.

67. As men advance in knowledge, their first conjectures appear silly and childish, and give place to others which agree 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.

Illus. Des Cartes thus conjectured, that the heavenly bodies 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 also, that the soul is seated in a small gland in the brain, called the pineal gland: that there, as in her presence chamber, she receives intelligence of every thing that affects the senses, by means of a subtile fluid contained in the nerves, and called animal spirits; and that she dispatches 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.

68. Such conjectures, in philosophical matters, have commonly received the name of hypotheses, or theories.

Obs. 1. And the invention of any hypothesis which, founded on some slight probabilities, 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

2. There is such proneness in men of genius to invent hypotheses, and in others to acquiesce in them, as the utmost that 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.

69. 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.

Obs. 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 would a thousand of the greatest wits whom the world ever produced, have, without any previous knowledge in anatomy, to 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.

70. Of all the discoveries that have been made concerning the inward structure of the human body, never one was made by conjecture.

Illus. 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 phisiologist 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.

71. 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.

Obs. Such discoveries have always been made by patient observation, by accurate experiments, or by conclusions drawn by strict resaoning from observations and experiments; and such discoveries have always tended to refute, but not to confirm, the theories and hyhotheses which ingenious men had invented.

Illus. 1. The finest productions of human art are immensely short of the meanest productions of nature. The nicest plumasier cannot make a feather. Nor could any society of chemists and meteorologists cover the hills with mists, and the face of the sky with clouds. Human workmanship will never bear a comparison with the workmanship of nature.

2. The Indian phiosopher being at a loss to know how the Earth was supported, invented the hypotheses of a huge elephant, on whose back it rested: and the elephant he supposed to stand on a huge tortoise. This hypothesis, how ridiculous soever it appears to us, might seem very reasonable to other Indians, who knew no more of it than the inventor, and never inquired, What did the tortoise stand on?

72. 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, how ancient soever, 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 sufficient

ly attested, is genuine and pure; it is the voice of Nature, and no fiction of humar imagination.

73. The first rule of philosophizing, laid down by the great Newton, is this:"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 the golden rule; it is the true and proper test, whereby what is sound and solid in philosophy may be distinguished from what is hollow and vain.

Corol. If a philosopher, therefore, pretend to show us the cause of any natural effect, whether relating to matter or mind; let us first consider whether there be sufficient evidence that the cause he assigns does really exist. If there be 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 have these two conditons, it is good for nothing.

CHAPTER IV.

OF ANALOGY.

74. Ir is natural to men to judge of things less known, by some similitude which they observe, or which they think they observe, between them and things more familiar or better known. This method of judging is called Analogy; and 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 considerable degrees of probability in conclusions drawn from analogy.

Illus. Thus we may observe a very great similitude between this Earth which we inhabit, and the other planets, Herschel, Saturn, Jupiter, Mars, Venus, and Mercury. They all revolve round the Sun, as the Earth does, although at different distances and in different periods of time. They all borrow their light from the Sun, as the Earth does. They revolve round their axes like the Earth round her axis, and, by that means, must have a regular succession of day and night. Some of them have moons, which 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; nay, of sentient natures. There is some probability in this conclusion from analogy.