The most representative, as, indeed, the most able, writer of the school of Common Sense is Thomas Reid (1710-1796). He was Professor first at Aberdeen and afterwards at Glasgow. Though he did not neglect moral subjects, his attention was chiefly directed to psychological questions. He was a man of truly philosophical spirit, with much Scotch shrewdness and caution—the embodiment of that "common sense" which he so often commends. His principal works are: Essays on the Intellectual Powers of Man, published in 1785, and Essays on the Active Powers, 1788.
Alarmed by the consequences which had been drawn by Hume from Locke's Empiricism, he was induced to study anew the origin of our perceptive faculties with the object of proving that the mind is cognisant of a real objective world. There are, therefore, two points around which his philosophy revolves;—the one is the criterion of the correct theory of sense-perception, and the other is the doctrine of a common sense, a criterion of truth.
The theory that we do not perceive objects immediately, but only through ideas, Reid holds to be a fiction, and the source of much mischievous error. He denies that we perceive by means of intermediate or representative ideas, or obtain knowledge of the external world by means of any reasoning whatever.
His own theory is that of immediate perception. We do not start with ideas, but with judgments. As soon as we have a sensation we have at the same time the knowledge of it as objective and the knowledge of it as our own. He holds, indeed, that there is first a sensation, and that the sensation "suggests" a perception. The word "suggestion" is an important one in Reid's philosophy. It was borrowed from Berkeley; but is implied by Reid to denote those "natural suggestions" or "judgments" of nature which are implied in the existence of all phenomena,— relations, in other words, which are necessary to the very constitution of experience.
These suggestions or judgments are the first great principles of the knowledge of self and the reality of the natural world. "If we attend," says Reid in a suggestive passage, "to that act of our mind, which we call the perception of an external object, we shall find in it these three things: First, some conception or notion of the object perceived; secondly, a strong and irresistible conviction and belief of its present existence; thirdly, that this conviction and belief are immediate and not the result of reasoning " (Works, p. 258).
Connected with this theory of perception is his doctrine of natural language or signs. "Our sensations are signs of external objects." There are, he holds, natural signs which suggest or conjure up a thing and create a belief that it exists. These suggestions are not images, he tells us,— only signs which irresistibly suggest the reality of objects. But, it may be asked, does not Reid in thus bringing in "signs" give away his whole theory of immediate perception? There is, after all, little difference between his theory of signs and that of "representative ideas" which he combats. He, too, virtually admits the necessity of some kind of medium.
Without pursuing further his theory of external perception, let us ask what is his criterion of knowledge or ultimate appeal—for this is really the distinctive feature of the school. "Common sense" is the acknowledged criterion. The phrase is ambiguous. It may mean "good sense," or wisdom, a gift by no means common. It may also mean a power or principle implanted in all minds by which we can judge and decide upon the truth or falsity of any proposition that is presented to us. As employed by Reid, both meanings are tacitly implied, though in general he means by it a certain principle in our constitution, which all men are obliged to admit and act upon. But while nothing sounds so plausible as an appeal to common sense, there is nothing so illusive or uncertain. My common sense may not be yours, and your answer to me may quite legitimately be, "I do not perceive it so"; and, in any case, to solve a problem by an appeal to common sense is virtually to acknowledge that the problem is insolvable.
In general, Reid falls back upon the existence in the human mind of certain necessary truths which belong to our very constitution, and which every sound mind must agree to. "By what principles of logic we make these inferences it is impossible to show." They do not fall within the province of reasoning, but of common sense. "They are judgments of nature immediately inspired by our constitution." They cannot be proved. They are the basis of all proof. He divides the principles of common sense into two classes,—those relating to "contingent truths" and those relating to "necessary truths." Among the first, he places the existence of everything of which I am conscious—self-identity; that things are what we perceive them to be; the freedom of the will; the life and intelligence of our fellowman ; and the uniformity of nature. Among the second, he places all mathematical truths and logical axioms; all principles of moral and metaphysical truths, as, for example, what begins to exist must have a cause, and that design may be inferred in the cause from marks in the effect. The main point on which Reid insists is that every perception is, or involves a judgment. This judgment is the unit of knowledge, and carries with it at once a belief in the perceiving subject as well as the object perceived.
Of the disciples of Reid it will not be necessary to speak in detail. Jas. Oswald (d. 1793) applied common sense to a consideration of religion. Jas. Beattie (1735-1803) wrote on the Nature and Immutability of Truth. Adam Ferguson (1724-1816) and Thomas Brown (1778-1820) sought to bring the teaching of Hume and Reid into closer union.
The chief representative of the school after Reid was Dugald Stewart (1753-1828), Professor in Edinburgh, whose chief work is The Elements of the Philosophy of the Human Mind.
Stewart follows his master in his attempt to classify the intellectual powers of man, but his list is somewhat defective and redundant. While he makes self-consciousness a separate attribute, he does not give to reason a distinct place. He speaks of "the fundamental laws of belief" rather than of the somewhat ambiguous principle of "common sense."
He is specially happy in treating of Memory and the Association of Ideas, though in dealing with "Causation" he seems to yield too much to the theory of Hume.
Though usually a fair critic of the writings of others, he does less than justice to Kant, whom he evidently knew only at second hand. But his reflections on Kant are not more misleading than are Kant's own observations on the school of Common Sense, which he caricatured in the preface to The Critique.
Whatever may be said of the shortcomings of the philosophy of Reid and Stewart, it must be admitted that it is a plea for necessary truth, and that it formed a timely and necessary check to the growing tide of scepticism which had begun to appear in this country and on the Continent towards the middle of the eighteenth century. The great work which the Scottish school achieved consists in its careful investigation of the faculties of the mind, and particularly of man's primary convictions.
In one sense, what Kant did, they too sought to do—to subject the mind to a critical analysis in order to discover its necessary and universal truths. That this analysis was not complete or thorough they themselves would be the first to admit. While their merit is, as against the scepticism of Hume, to have shown that there are intuitive or ultimate principles of the mind, their weakness is that they do not tell us what are the tests by which the presence of these truths may be detected. Too often these necessary truths are arbitrarily chosen, nor is any attempt made to bring the isolated intuitions to a rational unity. The opposition between subject and object is not solved, by the mere assertion that common sense assures us of the existence of both.
The position of the object as given along with the subject, which is the standpoint of the Scottish school, too often degenerates into a crude dualism of mind and matter as two heterogeneous substances.
The last thinker of this school is Sir Wm. Hamilton, who was one of the strongest philosophical minds which Britain has produced. Uniting the positions of Kant and Reid, his philosophy may be generally characterized as a vindication of the relativity of all knowledge, and therefore of the impossibility of attaining to a coherent view of the world.
Sir Wm. Hamilton was born at Glasgow in 1788. He studied in Scotland and Oxford, arts and medicine and law, and was admitted to the Scottish bar. In 1821 he was appointed Professor of Civil History in Edinburgh, and in 1837 was called to the chair of Logic and Metaphysics, which he held till his death in 1856. Besides his works on Philosophy, Literature, and Education, he wrote lectures on Logic and Metaphysics, which were published after his death.
The standpoint of Hamilton is what may be called Relativism. That is to say, he believes all that we perceive is the phenomenon, and that our knowledge of matter as well as of mind is confined to phenomenal states. Of existence absolutely and in itself we know nothing. Hamilton therefore is the advocate of natural realism. Since we know only the relations of things, and since relativity in this sense is a quality of all human knowledge, it follows that we cannot know the unconditioned. "To know is to condition." Conditional limitation is the fundamental law of the possibility of thought. But though the unconditioned is unknowable by reason, Hamilton strangely affirms that it is not a contradiction in itself. Revelation, he holds, supplements the knowledge which our faculties are too weak to wholly apprehend.
With regard to the self and the not-self, while maintaining that the doctrine of relativity applies to the pure objects of thought, i.e. that they are unknowable in themselves, he allows that our mental experience reveals itself as a unity amid change, and that our experience of the external world warrants us in representing it as a permanent reality.
The doctrine of relativity, of which Hamilton is the most noted champion, became later the basis of modern agnosticism as represented by Huxley and Tyndal. Dean Mansel, in his famous Bampton lectures on the Limits of Religious Thought in 1858, as well as in his Philosophy of the Conditioned (1866) applied this theory in the defence of religion. He seeks to refute rationalism by showing that as the only knowledge of the unconditioned which the human mind can acquire is negative, in matters of religion our reason is inadequate and must be supplemented by faith.
The last name we may mention here is that of James Ferrier (1808-1864), author of the Institutes of Metaphysics, who, though a Scotsman, was opposed to the doctrines of the Scottish philosophy. He had learned much from the German idealists, and was one of the earliest students of Hegel in this country, and thus prepared the way for a more adequate view of human consciousness.
The agnosticism of Hamilton and Mansel based upon the doctrine of Relativity has been most effectively dealt with by Ferrier. "That all knowledge," says Hamilton, "consists in a certain relation of the object known to the subject knowing is self-evident. . . . All qualities both of mind and of matter are therefore only known to us as relations: we know nothing in itself." In other words, we are necessarily cut off from knowing the real constitution of anything, because the intelligence can know only by means of its faculties of knowing. Even the Divine intelligence itself cannot know without knowing. As Ferrier puts it,—"There can be an ignorance only of that of which there can be a knowledge. That which is absolutely and necessarily unknowable to all intelligence is not a name for a hidden reality; it is simply another name for a contradiction, for nonsense." The doctrine of Relativity is thus a condemnation of all knowledge, because it fails to achieve an impossibility.(1)
(1) See A. Seth Pringle-Pattison, Scottish Philosophy, pp. 164-6