obtained by analysis. The peculiar use of the latter, is to aid our inquiries in the acquisition of knowledge; of the former, to facilitate the attainment of our designs in its communication. In proceeding according to the method of synthesis, we must be careful, in the first place, that our propositions be expressed in terms that are clearly and distinctly understood; that the words of our definitions be clearer than those they are brought to explain. Of what importance this rule is to reasonings in general, and especially to the synthetic mode of ratiocination, a slight acquaintance with the controversies that have engaged mankind, and with the way in which they have been conducted, will suf ficiently convince us. Even when the matter in dispute does not consist in a verbal ambiguity, the obscure and ill-defined language employed, exciting ideas that are only remotely, if at all, connected with the subject, diverts the mind from the avowed object of inquiry, and renders it far more difficult of clear apprehension, than at the commencement of the discussion. There is, therefore, no source of fallacy more dangerous, because more apt to be unperceived, than this, and against which it behoves every lover of truth to be constantly on his guard.

There is a second rule which we ought to observe in proceeding according to the way of synthesis; and that is, that the general truth on which our reasonings are founded be so clear and convincing, as to force the assent of any reasonable man. The general point

which we assume as the basis of our discussions must be self-evident, otherwise all our reasonings must be fallacious.

The third, and only other rule which I shall at pre

sent notice, as of essential importance in synthesis, is, that all the consequences we deduce be necessarily implied in the premises from which we set out. That it is only by rigidly prescribing this rule to ourselves, in our synthetic reasonings, we can hope to keep free of error, is very obvious; and yet, owing to misapprehension, or to ignorance, or to inattention, it is often left out of view, and a chain of reasoning is formed, the strength of which is greatly impaired by the slender ties by which many of its parts are held together. We cannot expect to escape this source of fallacy without clearness and accuracy of thought, and without cultivating habits of close attention.

5. The next mode of expression in use among philosophers, of which I shall take notice, is, the explanation of a phenomenon. It is generally supposed to be the peculiar advantage of philosophy, that it enables its votaries to ascertain the causes of things. How far this notion is correct, I shall not here stop to determine. It may be observed, however, that when we are said to explain any fact or appearance of nature, we mean no more than that we shew it to be necessarily included in some phenomenon or fact already known, or supposed to be known, and we consider one phenomenon as the cause of another, when we conceive the existence of the latter to depend on some power residing in the former. According to this observation, the limits of human knowledge are fixed, the real object of philosophy is ascertained, and we are the more likely to prosecute our inquiries with success, when we are previously aware of the extent to which it is allowed us to carry them.

6. When a fact which has no other evidence of its

reality than the explanation which it affords of certain appearances, is assumed for the sake of explaining these appearances, it is called an hypothesis*. That extreme fondness in the human mind for assigning the causes of the phenomena with which it is surrounded, has, in all ages, been the occasion of substituting hypothetical reasonings for patient experiment and observation. It is, besides, more flattering to the pride and vanity of man, as well as more agreeable to his indolence, to be able to account for phenomena by an ingenious hypothesis, than by an appeal to facts. And, accordingly, there is no lesson which he is more slow to learn, than that mere ingenuity can go but a very little way in explaining the phenomena of the universe; that before he can acquire sound knowledge, he must become the scholar of experience, and carry her along with him into all his researches, and that without the humility requisite to make this prac tical attainment, the more lofty the exertions of his genius, the more injurious will they prove to the progress of real science.

"I would," says Dr. Reid, in a letter to Lord Kaimes," I would discourage no man from conjecturing, only I wish him not to take his conjectures for knowledge, or to expect that others should do so. Conjecturing may be an useful step even in natural philosophy. Thus, attending to such a phenomenon,

* Newton simply defines that to be an hypothesis which is not deduced from an observation of facts: while he maintains that conjectures should have no place in experimental philosophy. "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."

I conjecture that it may be owing to such a cause. This may lead me to make the experiments or observations proper for discovering, whether that is really the cause or not; and if I can discover, either that it is, or is not, my knowledge is improved, and my conjecture was a step to that improvement. But while Į rest in my conjectures, my judgment remains in suspense, and all I can say is, it may be so, and it may be otherwise."

This is a very just view of the stress which ought in any case to be laid on hypothesis, and of the uses to which it may be applied. When it is employed simply as the means of stimulating our efforts in the pursuit of truth, urging us forward to the regions of certainty and knowledge, and not rested on as an ascertained and established fact, it cannot do injury, and it may do some good. It is melancholy to think, however, that this, more than any other cause, prevented the progress of reason and science during many ages, and that nearly all the labours of the most distinguished metaphysicians of modern times have been occupied in removing the rubbish which fanciful and fertile hypotheses had associated with the philosophy of the human mind. From the nature of this science, its remoteness from the comprehension of many of the species, and the facts which it analyzes, not being subjected to the evidence of our senses, it must be allowed, that it is more difficult to rescue it from the abuse of hypothesis, than chemistry or natural philosophy; but it forms no slight ground of encouragement, that even these branches of knowledge were once as full of absurd and fanciful conjectures as this;

and that the same rigid attention to the methods of analysis and induction, the only safe and successful way of pursuing philosophical inquiries, which has carried them to so high an eminence, may give the same commanding attitude to the study of our own intellectual and moral frame. Truth is one, and those who are animated by the love of it, have no cause to fear that in any department of nature it is entirely removed beyond the reach of the human faculties, or that humility and industry, connected with definite notions of the proper objects of inquiry, will not be rewarded with more just and comprehensive views of the structure and operations of the human mind.