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It may make this brief sketch more clear, to notice a circumstance in the history of philosophy, which, perhaps, serves better in an incidental manner to mark the boundaries of the field of Hume's inquiry, than many pages of discursive description. The transcendentalists took him up as having examined the materials solely, on which pure reason operates; [77]not pure reason itself. They said that he had examined the classes of matter which come before the judge, but had omitted to describe the judge himself, the extent of his jurisdiction, and his method of enforcing it. They maintained, that all these things, which with Hume appeared to be the constituent elements of philosophy, were nothing but the materials on which philosophy works,—that to presume them to be of service presupposed a reason which could make use of them,—that Hume himself, while thus speculating and telling us that his mind consisted but of a string of ideas, left behind by certain impressions, was himself making use of that pure reason which was in him before the ideas or impressions existed, and was through that power adapting the impressions and ideas to use. He characterized his system as "an attempt to introduce the experimental method of reasoning into moral subjects:" but they said that there was another and a preliminary matter of inquiry—the faculty, to speak popularly, which suggested what experiments should be made, and judged of their results.

Hume may be found indirectly lamenting the fate of his own work on metaphysics, in his remarks on other works of a kindred character; and in these criticisms we have a clue to the expectations he had formed. In his well-known rapid criticism on the literature of the epoch of the civil wars, he says of Hobbes: "No author in that age was more celebrated both abroad and at home than Hobbes. In our times, he is much neglected: a lively instance how precarious all reputations founded on reasoning and philosophy! A pleasant comedy which paints the manners of the age, and exposes a faithful picture of nature, is a durable work, and is transmitted to the latest posterity. But a system, whether physical or metaphysical, owes commonly its [78]success to its novelty; and is no sooner canvassed with impartiality, than its weakness is discovered."

Like the majority of literary prophecies dictated by feeling and not by impartial criticism, this one, whether as it refers to "The Leviathan," of which it is ostensibly uttered, or to the "Treatise of Human Nature," the fate of which doubtless suggested it, has proved untrue. The influence of Hobbes has revived, as that of the Treatise remained undiminished from the time when it was first fully appreciated. And in both cases their influence has arisen from that element which seems alone to be capable of giving permanent value to metaphysical thought. It is not that in either case the fundamental theory of the author is adopted, as the disciples of old imbibed the system of their masters, but that each has started some novelties in thought, and, either by themselves sweeping away prevailing fallacies, or suggesting to others the means of doing so, have cleared the path of philosophy. As a general system, the philosophy of Hobbes has been perhaps most completely rejected at those times when its incidental discoveries and suggestions made it most serviceable to philosophy, and were the cause of its being most highly esteemed. "Harm I can do none," says Hobbes, when speaking of the metaphysicians who preceded him, "though I err not less than they, for I leave men but as they are, in doubt and dispute." There is indeed nothing in the later history of metaphysical writing to show that the triumphs in that department of thought are to stretch beyond the establishment of incidental truths, the removal of fallacies, and the suggestion of theories that may teach men to think. The field is a republic: incidental merit has its praise, and is allowed its pre-eminence; but no one mind, it may safely be pronounced, holds [79]in it that monarchical sway which Adam Smith retains over the empire of political economy. The ancient systems anterior to Christianity allowed of such empire. The pupil did not follow his master merely in this and that incidental truth developed, but adopted the system in all its details and proportions as his system and his creed. In later times it would probably be found that the most devoted admirers of great writers on metaphysics do not adopt their opinions in the mass; and it seems that men must now go elsewhere than to the produce of human reason, for the grand leading principles of the philosophy of belief and disbelief.

To those who hold that the writings of the great metaphysicians are thus to be esteemed on account, not of their fundamental principles, but of the truths they bring out in detail, a new theory is like a new road through an unfrequented country, valuable, not for itself, but for the scenery which it opens up to the traveller's eye. The thinker who adopts this view, often wonders at the small beginnings of philosophical systems—wonders, perhaps, at the circumstance of Kant having believed that his own system started into life at one moment as he was reading Hume's views of Cause and Effect. But the solution is ready at hand. We feel that the philosopher of Knigsberg had in his mind the impulses that would have driven him into a new path had no Hume preceded him. We owe it to the Essay on Cause and Effect that it was the starting-point at which he left the beaten track; but, had it not attracted his attention, his path would have been as original, though not, perhaps, in the same direction. And so of Hume himself. If the main outline of his theory had never occurred to him, he would still have been a great philosopher; for in some form or other he would have [80]found his way to those incidental and subsidiary discoveries, which are admitted to have reality in them by many who repudiate his general theory.

Of all the secondary applications of the leading principle of the Treatise, none has perhaps exercised so extensive an influence on philosophy, as this same doctrine of cause and effect. Looking to those separate phenomena, of which in common language we call the one the cause of the other, and the other the effect of that cause, he could see no other connexion between them than that the latter immediately followed the former. He found that the mind, proceeding on the inductive system, when it repeatedly saw two phenomena thus conjoined, expected, when that which had been in use to precede the other made its appearance, that the other would follow; and he found that by repeated experiment this expectation might be so far strengthened, that people were ready to stake their most important temporal interests on the occurrence of the phenomenon called the effect, when that called the cause had taken place. But if there were any thing else but this conjunction, of which a knowledge was demanded—if the unsatisfied investigator sought for some power in the one phenomenon which enabled it to be the fabricator of the other—the sceptical reasoner would answer, that for all he could say to the contrary such a thing might be, but he had no clue to that knowledge—no impression of any such quality passed into his intellect through sensation—his mind had no material committed to it by which the existence or non-existence of any such thing could be argued.

The vulgar notion of this theory was, that it destroyed all our notions of regularity and system in the order of nature; that it made no provision for [81]unseen causes, and contemplated only the application of the doctrines of cause and effect to things which were palpably seen following each other. But the inventor of the theory never questioned the regularity of the operations of nature as established by the inductive philosophy; he only endeavoured to show how far and within what limits we could acquire a cognizance of the machinery of that regularity. He denied not that when the spark was applied, the gunpowder would ignite, or that when the ball was dropped, it would proceed to the earth with the accelerated motion of gravitation; but he denied that we could see any other connexion between the cause and effect in either case, than that of uniform sequence. When it was scientifically adopted, the theory was found to be productive of the most important results. The view that when any effect was observed, that phenomenon which was most uniform in its precedence was the one entitled to be termed the cause, was a salutary incentive to close and patient investigation, by laying before the philosopher the simple, numerical question—what was that phenomenon which, by the uniformity of its precedence, was entitled to be termed the cause?[81:1] The test became of the simplest kind; and, if the experimentalist had at a particular time considered some phenomenon as a cause,—if the farther progress of patient and unprejudiced inquiry showed that [82]another, by the occurrence of instances in which it preceded the effect while the former did not, had a preferable title to be termed the cause, the mind in its unbiassed estimate of numbers at once admitted the claim. But when, according to the antagonist system,[82:1] it became settled that any given phenomenon had in it the power of bringing into existence another, that power was viewed as a quality of the object. When things are admitted to have qualities, it is not easy for the mind at once to assent to their non-existence and to admit that others have the proper title to these qualities. Analogy, the great source of fallacies, comes to increase the difficulty, by a confusion of what are termed the qualities of bodies, and those endowments with which we invest our fellow-creatures. In this respect Hume's theory of cause and effect has been of great service to inductive philosophy.