phical to attempt an explanation of perception, or of the affociation of ideas, upon mechanical principles; than it would be to explain the phenomena of gravitation, by fuppofing, as fome of the ancients did, the particles of matter to be animated with principles of motion; or to explain the chemical phenomena of elective attractions, by fuppofing the fubftances among which they are obferved, to be endowed with thought and volition. The analogy of matter, therefore, can be of no ufe in the inquiries which form the object of the following work; but, on the contrary, is to be guarded against, as one of the principal fources of the errors to which we are liable.

Among the different philofophers who have fpeculated concerning the human mind, very few indeed can be mentioned, who have at all times been able to guard against analogical theories. At the fame time, it must be acknowledged, that fince the publication of Des Cartes' writings, there has been a gradual, and, on the whole, a very remarkable improvement in this branch of fcience. One ftriking proof of this is, the contraft between the metaphyfical fpeculations of fome of the moft eminent philofophers in England at the end of the laft century, and those which we find in the fyftems, however imperfect, of the prefent age. Would any writer now offer to the world, fuch conclufions with refpect to the mind, as are contained in the two following paffages from Locke and Newton? "Habits," (fays Locke,)" feem to be but trains of motion, in "the animal fpirits, which, once fet a-going, continue

"in the fame fteps they had been used to, which,

by often treading, are worn into a smooth path." And Newton himself has propofed the following query, concerning the manner in which the mind perceives external objects. "Is not," (fays he,) "the fenforium of animals the place where the fen"tient fubftance is prefent, and to which the fenfi"ble fpecies of things are brought, through the "nerves and brain, that they may be perceived by "the mind present in that place?"-In the course of the following Effays, I fhall have occafion to quote various other paffages from later writers, in which an attempt is made to explain the other phenomena of mind, upon fimilar principles.

It is however much to be regretted, that even fince the period when philofophers began to adopt a more rational plan of inquiry with refpect to fuch fubjects, they have been obliged to spend fo much of their time in clearing away the rubbish collected by their predeceffors. This indeed was a preliminary step, which the state of the fcience, and the conclufions to which it had led, rendered abfolutely neceffary; for, however important the pofitive advantages may be, which are to be expected from its future progrefs, they are by no means fo effential to human improvement and happiness, as a fatisfactory refutation of that fceptical philofophy, which had ftruck at the root of all knowledge, and all belief. Such a refutation feems to have been the principal object which Dr. Reid propofed to himself in his metaphyfical inquiries; and to this object his labours have been directed with fo much ability, candour,

and perfeverance, that unless future fceptics fhould occupy a ground very different from that of their predeceffors, it is not likely that the controverfy will ever be renewed. The rubbish being now removed, and the foundations laid, it is time to begin the fuperftru&ture. The progrefs which I have made in it is, I am fenfible, very inconfiderable; yet I flatter myself, that the little I have done, will be fufficient to illuftrate the importance of the ftudy, and to recommend the fubjects of which I am to treat, to the attention of others.

After the remarks which I have now made, the reader will not be furprifed to find, that I have ftudioufly avoided the confideration of thofe queftions which have been agitated in the prefent age, between the patrons of the fceptical philofophy, and their opponents. Thefe controverfies have, in truth, no peculiar connexion with the inquiries on which I am to enter. It is indeed only by an examination of the principles of our nature, that they can be brought to a fatisfactory conclufion; but fuppofing them to remain undecided, our fceptical doubts concerning the certainty of human knowledge, would no more affect the philofophy of mind, than they would affect any of the branches of phyfics; nor would our doubts concerning even the existence of mind, affect this branch of fcience, any more than the doubts of the Berkeleian, concerning the existence of matter, affect his opinions in natural philofophy.

To what purposes the philofophy of the human mind, according to the view which I propofe to take of it, is fubfervient, I fhall endeavour to explain, at fome length, in the following fection.

PART SECOND.

SECTION I.

Of the Utility of the Philofophy of the Human Mind.

IT has been often remarked, that there is a mutual

connexion between the different arts and sciences; and that the improvements which are made in one branch of human knowledge, frequently throw light on others, to which it has apparently a very remote relation. The modern difcoveries in aftronomy, and in pure mathematics, have contributed to bring the art of navigation to a degree of perfection formerly unknown. The rapid progrefs which has been lately made in aftronomy, anatomy, and botany, has been chiefly owing to the aid which these sciences have received from the art of the optician.

Although, however, the different departments of fcience and of art mutually reflect light on each other, it is not always neceffary either for the philofopher or the artist to aim at the acquifition of general knowledge. Both of them may fafely take many principles for granted, without being able to demonftrate their truth. A feaman, though ignorant of mathematics, may apply, with correctnefs and dexterity, the rules for finding the longitude: An aftronomer, or a botanist, though ignorant of optics, may avail himself of the use of the telescope, or the microscope.

C

Thefe

Thefe obfervations are daily exemplified in the cafe of the artift; who has feldom either inclination or leisure to fpeculate concerning the principles of his art. It is rarely, however, we meet with a man of fcience, who has confined his ftudies wholly to one branch of knowledge. That curiofity, which he has been accuftomed to indulge in the course of his favourite purfuit, will naturally extend itfelf to every remarkable object which falls under his obfervation; and can fcarcely fail to be a fource of perpetual diffatisfaction to his mind, till it has been fo far gratified as, to enable him to explain all the various phenomena, which his profeffional habits are every day prefenting to his view.

As every particular fcience is in this manner connected with others, to which it naturally directs the attention, fo all the purfuits of life, whether they terminate in fpeculation or action, are connected with that general fcience, which has the human mind for its object. The powers of the understanding are inftruments which all men employ; and his curiofity must be fmall indeed, who paffes through life in a total ignorance of faculties, which his wants and neceffities force him habitually to exercife, and which fo remarkably distinguish man from the lower animals. The active principles of our nature, which, by their various modifications and combinations, give rife to all the moral differences among men, are fitted, in a ftill higher degree, if poffible, to intereft thofe, who are either difpofed to reflect on their own characters, or to obferve, with attention, the characters of others. The phenomena re.

fulting