ther (for example) the cause of gravitation be material or im- Introduction. material, is a point about which two Newtonians may differ, while they agree perfectly in their phyfical opinions. It is fufficient, if both admit the general fact, that bodies tend to approach each other, with a force varying with their mutual distance, according to a certain law. In like manner, in the study of the human mind, the conclufions to which we are led, by a careful examination of the phenomena it exhibits, have no neceffary connexion with our opinions concerning its nature and effence.-That when two fubjects of thought, for inftance, 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 fenfes; and it is plainly a fact totally unconnected with any hypothefis concerning the nature of the foul, and which will be as readily admitted by the materialist as by the Berkeleian.

NOTWITHSTANDING, however, the reality and importance of this diftinction, it has not hitherto been fufficiently attended to, by the philofophers 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 fteadily in view, in all his inquiries. In the writings, indeed, of several other modern Metaphysicians, we meet with a variety of important and well-afcertained facts; but, in general, these facts are blended with speculations upon fubjects which are placed beyond the reach of the human faculties.It is this mixture of fact, and of hypothefis, which has

brought

Introduction. brought the philofophy of mind into fome degree of difcredit; nor will ever its real value be generally acknowledged, till the distinction I have endeavoured to illuftrate, be understood, and attended to, by those who speculate on the subject. By confining their attention to the fenfible qualities of body, and to the fenfible phenomena it exhibits, we know what discoveries natural philofophers have made and if the labours of Metaphyficians fhall ever be rewarded with fimilar fuccefs, it can only be, by attentive and patient reflection on the fubjects of their own consciousness.

I CANNOT help taking this opportunity of remarking, on the other hand, that if physical inquirers fhould think of again employing themselves in speculations about the nature of matter, instead of attempting to ascertain its fenfible properties and laws, (and of late there feems to be fuch a tendency among fome of the followers of Bofcovich,) they will foon involve themselves in an inextricable labyrinth, and the firft principles of phyfics will be rendered as myfterious and chimerical, as the pneumatology of the school-men.

THE little progrefs which has hitherto been made in the philosophy of mind, will not appear surprising to those who have attended to the hiftory of natural knowledge. It is only fince the time of Lord Bacon that the ftudy of it has been profecuted with any degree of fuccefs, or that the proper method of conducting it has been generally underftood. There is even some reason for doubting, from the crude fpeculations on medical and chemical subjects which are daily offered to the public,

whether

whether it be yet understood so completely as is commonly ima- Introduction. gined; and whether a fuller illustration of the rules of philofophifing, than Bacon or his followers have given, might not be ufeful, even to phyfical inquirers.

WHEN We reflect, in this manner, on the fhortness of the period during which natural philofophy has been fuccessfully cultivated; and, at the fame time, confider how open to our examination the laws of matter are, in comparison of those which regulate the phenomena of thought, we shall neither be difpofed to wonder, that the philofophy of mind should still remain in its infancy, nor be discouraged in our hopes concerning its future progrefs. The excellent models of this fpecies of investigation, which the writings of Dr. Reid exhibit, give us ground to expect that the time is not far diftant, when it shall affume that rank which it is entitled to hold, among the sciences.

It would probably contribute much to accelerate the progress of the philosophy of mind, if a distinct explanation were given of its nature and object; and if some general rules were laid down, with respect to the proper method of conducting the study of it. To this fubject, however, which is of fufficient extent to furnish matter for a separate work, I cannot attempt to do juftice at prefent; and fhall 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 inquiries.

Introduction.

UPON a flight attention to the operations of our own minds, they appear to be fo complicated, and fo infinitely diverfified, that it seems to be impoffible to reduce them to any general laws. In confequence, however, of a more accurate examination, the profpect clears up; and the phenomena, which appeared, at firft, 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 fame place in the philofophy of mind, that the general laws we investigate in phyfics, 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 cafes, a knowledge of these laws leads to an explanation of an infinite number of phenomena.

IN the investigation of phyfical laws, it is well known, that our inquiries must always terminate in fome general fact, of which no account can be given, but that fuch is the conftitution of nature. After we have established, for example, from the astronomical phenomena, the universality of the law of gravitation, it may still be afked, whether this law implies the constant agency of mind; and (upon the fuppofition that it does) whether it be probable that the Deity always operates immediately, or by means of fubordinate inftruments? But thefe queftions, however curious, do not fall under the province of the natural philofopher. It is fufficient for his purpose, if the universality of the fact be admitted.

THE

• THE cafe is exactly the fame in the philofophy of mind. Introduction. When we have once afcertained a general fact; fuch as, the various laws which regulate the affociation 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 fcience. If we proceed no farther than facts for which we have the evidence of our own confcioufnefs, our conclufions will be no less certain, than those in physics: but if our curiofity leads us to attempt an explanation of the association of ideas, by certain fuppofed vibrations, or other changes, in the state of the brain; or to explain memory, by means of supposed impresfions and traces in the fenforium; we evidently blend a collection of important and well-afcertained truths, with principles which reft wholly on conjecture *.

THE

*There is indeed one view of the connexion between Mind and Matter, which is perfectly agreeable to the just rules of philofophy. The object of this is, to ascertain the laws which regulate their union, without attempting to explain in what manner they are united.

Lord Bacon was, I believe, the first who gave a diftinct idea of this fort of fpeculation; and I do not know that much progress has yet been made in it. In his books de Augmentis Scientiarum, a variety of subjects are enumerated, in order to illustrate its nature; and, undoubtedly, most of these are in a high degree curious and important. The following lift comprehends the chief of those he has mentioned; with the addition of several others, recommended to the confideration of Philofophers and of Medical Inquirers, by the late Dr. Gregory. See his Lectures on the Duties and Qualifications of a Physician.

1. The doctrine of the prefervation and improvement of the different fenfes.

2. The history of the power and influence of imagination.

3. The hiftory of the feveral species of enthusiasm.