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In what sense this celebrated maxim ought to be understood, I shall endeavour to shew more particularly, if I should live to execute a plan which I have long meditated, of analyzing the logical processes by which we are conducted to the different classes of truths, and of tracing the different kinds of evidence to their respective sources in our intellectual frame. For my present purpose, it is sufficient to observe, in general, that however universally the maxim may be supposed to apply to our knowledge of facts, whether relating to external nature, or to our own minds, we must, nevertheless, presuppose the existence of some intellectual capacities or powers in that being by whom this knowledge is to be acquired; powers which are necessarily accompanied, in their exercise, with various simple notions, and various ultimate laws of belief, for which experience is altogether incompetent to acHow is it possible, for example, to explain, upon this principle alone, by any metaphysical refinement, the operations of that reason which observes these phenomena; which records the past; which looks forward to the future; which argues synthetically from things known, to others which it has no opportunity of subjecting to the examination of the senses; and which has created a vast science of demonstrated truths, presupposing no knowledge whatever but of its own definitions and axioms? To say that, even in this science, the ideas of extension, of figure, and of quantity, are originally acquired by our external senses, is a childish play upon words, quite foreign to the point
at issue. Is there any one principle from which Euclid deduces a single consequence, the evidence of which rests upon experience, in the sense in which that word is employed in the inductive logic? If there were, geometry would be no longer a demonstrative science.
Nor is this all. The truths in mathematics (admitting that of the hypotheses on which our reasonings proceed) are eternal and necessary; and consequently (as was early remarked, in opposition to Locke's doctrine), could never have been inferred from experience alone. "If Locke," says Leibnitz, "had sufficiently considered the difference between "truths which are necessary or demonstrative, and "those which we infer from induction alone, he "would have perceived, that necessary truths could "only be proved from principles which command "our assent by their intuitive evidence; inasmuch
as our senses can inform us only of what is, not "of what must necessarily be." *
But, even with respect to facts, there are certain limitations with which this maxim must be received. Whence arises our belief of the continuance of the laws of nature? Whence our inferences from the past to the future? Not surely from experience alone. Although, therefore, it should
*"Si I.ockius discrimen inter veritates necessarias seu demonstratione perceptas, et eas quæ nobis sola inductione ut66 cunque innotescunt, satis considerasset,-animadvertisset, ne❝cessarias non posse comprobari, nisi ex principiis menti insitis; 66 cum sensus quidem doceant quid fiat, sed non quid necessario "fiat."-Tom. V. p. 358. (Edit. Dutens.)
be granted, as I readily do, that in reasoning concerning the future, we are entitled to assume no fact as a datum which is not verified by the experience of the past (which, by the way, is the sole amount of Bacon's aphorism), the question still remains, what is the origin of our confident belief, that past events may be safely assumed as signs of those which are yet to happen? The case is precisely the same with the faith we repose in human testimony; nor would it be at all altered, if, in the course of our past experience, that testimony had not once deceived us. Even, on that supposition, the question would still recur, whence is it we conclude, that it will not deceive us in future? or (what comes nearly to the same thing) that we give any credit to the narratives of men who existed two thousand years ago? No proposition, surely, can be more evident than this, that experience, in the acceptation in which Locke and his followers profess to understand it, can inform us of nothing but what has actually fallen under the retrospect of memory. -Of the truth and importance of these considerations, no philosopher seems to have been fully aware, previous to Mr Hume. "As to past experience," he observes," it can be allowed to give direct and "certain information of those precise objects only, "and that precise period of time, which fell under "its cognizance; but why this experience should be "extended to future times, and to other objects,— "this is the main question on which I would in❝ sist. 99* What is the proper answer to this ques
* See Hume's Essay, entitled Sceptical Doubts, &c.
tion is of no moment to our present argument. It is sufficient, if it be granted, that Experience alone does not afford an adequate explanation of the fact.
In concluding this Essay, it may not be altogether useless to remark the opposite errors which the professed followers of Bacon have committed, in studying the phenomena of Matter, and those of Mind. In the former, where Bacon's maxim seems to hold without any limitation, they have frequently shewn a disposition to stop short in its application; and to consider certain physical laws (such as the relation between the force of gravitation, and the distance of the gravitating bodies), as necessary truths, or truths which admitted of a proof, a priori; while, on the other hand, in the science of Mind, where the same principle, when carried beyond certain limits, involves a manifest absurdity, they have attempted to extend it, without one single exception, to all the primary elements of our knowledge, and even to the generation of those reasoning faculties which form the characteristical attributes of our species.
ON THE METAPHYSICAL THEORIES OF HARTLEY, PRIESTLEY, AND DARWIN.
WHEN I hinted, in the preceding Essay, that the doctrines prevalent in this country, with respect to the origin of our knowledge, were, in general, more precise and just than those adopted by the disciples of Condillac, I was aware that some remarkable exceptions might be alleged to the universality of my observation. Of those, indeed, who, in either part of the united kingdom, have confined their researches to the Philosophy of the Human Mind, properly so called, I do not recollect any individual of much literary eminence, who has carried Locke's principle to such an extravagant length as Diderot and Helvetius; but, from that class of our authors, who have, of late years, been attempting to found a new school, by jumbling together scholastic metaphysics and hypothetical physiology, various instances might be produced of theorists, whose avowed opinions on this elementary question, not only rival, but far surpass those of the French Materialists, in point of absurdity.
Among the authors just alluded to, the most