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As all our knowledge of the material world is de. rived from the information of our senses, natural philosophers have, in modern times, wisely abandoned to metaphysicians, all speculations concerning the nature of that substance of which it is composed ; concerning the possibility or impossibility of its being created; concerning the efficient causes of the chan. ges which take place in it; and even concerning the reality of its existence, independent of that of percipient beings: and have confined themselves to the humbler province of observing the phenomena it exhibits, and of ascertaining their general laws. By pursuing this plan steadily, they have, in the course of the two last centuries, formed a body of science, which not only does honor to the human understanding, but has had a most important influence on the practical arts of life. This experimenta. philosophy, no one now is in danger of confounding with the metaphysical speculations already mentioned. Of the importance of these, as a separate branch of study, it is possible that some may think more favorably than others; but they are obviously different in their nature, from the investigations of physics ; and it is of the utmost consequence to the evidence of this last science, that its principles should not be blended with those of the former.

A fimilar distinction takes place among the ques. tions which may be stated relative to the human mind.-Whether it be extended or unextended; whether or not it has any relation to place; and (if it has) whether it resides in the brain, or be spread over the body, by diffusion; are questions perfectly analogous to those which metaphysicians have started on the subject of matter. It is unnecessary to inquire at present whether or not they admit of answer. It is sufficient for my purpose to remark, that they are as widely and obviously different from the view which I propose to take, of the human mind in the following work, as the reveries of Berkeley concern. ing the non-existence of the material world, are from the conclusions of Newton and his followers. It is farther evident, that the metaphysical opinions, which we may happen to have formed concerning the nature either of body or of mind, and the efficient causes by which their phenomena are produced, have no necessary connexion with our enquiries concern. ing the laws, according to which these phenomena take place.-Whether (for example) the cause of gravitation be material or immaterial, is a point about which two Newtonians may differ, while they agree perfectly in their physical opinions. It is fufficient if both admit the general fact, that bodies tend to approach each other, with a torce varying with their mutual distance, according to a certain law. In like manner in the study of the human mind, the conclusion to which we are led by a careful examination of the phenomena it exhibits, have no necessary connexion with our opinions concerning its nature and effence. That when two subjects of thought, for instance, have been repeatedly presented to the mind in conjunction, the one has a tendency to suggest the other, is a fact of which I can no more doubt, than of any thing for which I have the evidence of my senses ; and it is plainly a fact totally unconnected with any hypothesis concerning the nature of the foul, and which will be as readily admitted by the materialist as by the Berkeleian.

prove to the contrary, it is possible, that the unknown substance which has the qualities of extension, figure, and colour, may be the same with the unknown substance which has the attributes of feeling, thinking and willing. But besides that this is only an hypothesis, which amounts to nothing more than a mere possibility, even if it were true, it would no more be proper to say of mind, that it is material, than to say of body, that it is spiritual.

Notwithstanding, however, the reality and importance of this distinction, it has not hitherto been

fufficiently attended to, by the philosophers who have treated of the human mind. Dr. Reid is perhaps the only one who has perceived it clearly, or at least who has kept it steadily in view, in all his inqui. ries. In the writings, indeed, of several other mod. ern metaphysicians, we meet with a variety of important and well ascertained facts ; but in general, these facts are blended with speculations upon sub. jects which are placed beyond the reach of the human faculties. It is this mixture of fact, and of hypothesis, which has brought the philosophy of mind into fome degree of discredit ; nor will ever its real value be generally acknowledged, till the distinction I have endeavoured to illustrate, be understood, and attend. ed to, by those who speculate on the subject. By confining their attention to the sensible qualities of body, and to the sensible phenomena it exhibits, we know what discoveries natural philosophers have made : and if the labours of Metaphysicians shall ever be rewarded with similar success, it can only be, by attentive and patient reflection on the subjects of their own consciousness,

I cannot help taking this opportunity of remarking on the other hand, that if physical inquirers should think of again employing themselves in speculations about the nature of matter, instead of attempting to ascertain its sensible properties and laws, (and of late there seems to be such a tendency among some of the followers of Boscovich,) they will foon involve themfelves in an inextricable labyrinth, and the first principles of physics will be rendered as mysterious and chimerical, as the pneumatology of the school-men.

The little progress which has hitherto been made in the philosophy of mind, will not appear surprising to those who have attended to the history of natural knowledge. It is only fince the time of Lord Bacon, that the study of it has been profecuted with any degree of success, or that the proper method of conducting it has been generally understood. There is even some reason for doubting, from the crude fpeculations on medical and chemical subjects which are daily offered to the public, whether it be yet underftood so completely as is commonly imagined ; and whether a fuller illustration of the rules of philosophising, than Bacon or his followers have given, might not be useful, even to physical inquirers.

When we reflect, in this manner, on the shortness of the period during which natural philosophy has been successfully cultivated ; and at the same time, consider how open to our examination the laws of matter are, in comparison of those which regulate the phenomena of thought, we shall neither be disposed to wonder, that the philosophy of mind should still remain in its infancy, nor be discouraged in our hopes concerning its future progress. The excellent models of this species of investigation, which the writings of Dr. Reid exhibit, give us ground to expect that the time is not far diftant when it shall as. fume that rank which it is entitled to hold among the sciences.

It would probably contribute much to accelerate the progress of the philofophy of mind, if a distinct explanation were given of its nature and object; and if fome general rules were laid down, with refpect to the proper method of conducting the study of it. To this subject, however, which is of sufficient extent to furnish matter for a separate work, I cannot attempt to do justice at present ; and shall therefore confine myself to the illustration of a few fundamental principles, which it will be of effential importance for us to keep in view in the following inquirers.

Upon a flight attention to the operations of our own minds, they appear to be so complicated, and so infinitely diversified, that it seems to be impossible to reduce them to any general laws. In consequence, however, of a more accurate examination, the profpect clears up; and the phenomena, which appeared, at first, to be too various for our comprehension, are found to be the result of a comparatively small number of simple and uncompounded faculties, or of fimple and uncompounded principles of action. These faculties and principles are the general laws of our conftitution, and hold the same place in the philosophy of mind, that the general laws we investigate in physics, hold in that branch of science. In both cases, the laws which nature has established, are to be investigated only by an examination of facts; and in both cases, a knowledge of these laws leads to an explanation of an infinite number of phenomena.

In the investigation of physical laws, it is well known, that our inquiries niuft always terminate in fome general fact, of which no account can be given, but that such is the constitution of nature. After we have established, for example, from the aftronomical phenomena, the univerfality of the law of gravitation, it may still be asked, whether this law implies the constant agency of mind; and (upon the supposition that it does) whether it be probable that the Deity always operates immediately, or by means of subordinate inftruments ? But these questions, however curious, do not fall under the province of the natural philofopher. It is fufficient for his purpose, if the univerfality of the fact be adınitted.

The case is exactly the same in the philosophy of mind. When we have once ascertained a generai fact; such as, the various laws which regulate the association of ideas, or the dependence of memory on that effort of the mind which we call Attention; it is all we ought to aim at, in this branch of science. If we proceed no farther than facts for which we have the evidence of our own conscious. nefs, our conclufions will be no less certain, than thofe in physics : but if our curiosity leads us to at

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