REID, THOMAS: Philosopher; b. at Strachan (19 m. s.w. of Aberdeen), Kincardineshire, Scotland, Apr. 26, 1710; d. at Glasgow Oct. 7, 1796. He graduated at Marischal College, Aberdeen, in 1728, where he was librarian 1733-36; was ordained in 1737, and presented by King's College, Aberdeen, to the living of New Machar twelve miles from the city. He engaged in speculative studies and in 1748 contributed an Essay upon Quantity, attacking Francis Hutcheson's application of mathematical formulas to ethical questions. In 1751 he succeeded to the regentship of King's College, which meant the professorship of philosophy, and his lectures included mathematics and. physics as well as logic and ethics. In 1758 he was one of the founders of the Philosophical Society which lasted till 1773, and from its discussions and his personal study, especially of the writings of David Hume (q.v.), arose An Inquiry into the Human Mind, on the Principles of Common Sense (Edinburgh, 1764), which led to the title, "philosophy of common sense," by which his system and that of his successors came to be known; and also, in 1764, to his election to the professorship of moral philosophy at Glasgow, which he held until his death, lecturing on theology, ethics, political science, and rhetoric.

Starting out with the empiricism of Locke and the philosophy of ideas unsupported by reality as culminating in Hume, Reid went further and claimed that our belief in an external world of space must be accepted as original datum of common sense. "Common sense" was not, however, to be taken as mere vulgar opinion, but as knowledge common to rational beings as such, or the principles of the human understanding. Reid set himself the task of developing a system for the refutation of the skepticism of Hume, against the theory of ideas previously in favor among philosophers. But in doing this he acknowledged that he was indebted to Hume for rousing him to the task of criticizing the popular philosophy, and of endeavoring to replace it by another which could endure the test of skeptical argumentation. His Inquiry into the Human Mind is an investigation into the relations of mind to the special senses, dealing in succession with smelling, tasting, hearing, touch, and sight. The work shows that Reid had given considerable attention to the physiology of the senses. His main purpose is to show ample warrant for trusting the information gathered by the senses, and constructing a theory of things by the application of rational principles. Unhappily his favorite phrase, "common sense," is at times used with apparent contradiction, but he means to disavow common sense as called in support of the current philosophy of ideas which had furnished skepticism with its weapons; and, on the other hand, to make common sense the basis of his principles of universal knowledge. Thus he wrote: "In reality, common sense holds nothing of philosophy, nor needs her aid. But, on the other hand, philosophy (if I may be permitted to change the metaphor) has no other root but the principles of common sense" (Inquiry, iv.). By this he means that the essential conditions of intelligence are given to all men, so that intellect does not wait on philosophy for warrant of her procedure; while, on the contrary, all sound philosophy must start with unreserved acknowledgment of the principles of intelligence, which he would name "common sense." To find out what these principles are was to him the necessary and most momentous task of a philosophy.

The form of philosophy which Reid had thus described and introduced he further vindicated and developed in his Essays on the Intellectual Powers of Man (1785), and Essays on the Active Powers of Man (1788). His first and essential position was gained in showing that the use of the senses implies constant exercise of judgment, and that this implies fundamental principles of thought which could be neither demonstrated, disputed, nor dispensed with. His next position was reached in laying open to view certain first principles in reasoning which are essential to intelligence. "'The judgment follows the apprehension of them necessarily; and both are equally the work of nature and the result of our original powers" (Intellectual Powers, essay vi., chap. iv.). These are axioms, first principles, principles of common sense, common notions, self-evident truths. His third position was reached when he entered the domain of morals, and maintained, in reference to knowledge of moral truths, that there "must be in morals, as in other sciences, first principles which do not derive their evidence from any antecedent principles, but may be said to be intuitively discerned" (Intellectual Powers, vii. 2). In treating of judgment as the ruling power in mind, he distinguished two functions: to reason, and to recognize first principles apart from reasoning. "We ascribe to reason two offices or two degrees. The first is to judge of things self-evident; the second is to draw conclusions that are not self-evident from those that are. The first of these is the province, and the sole province, of common sense; and therefore it coincides with reason in its whole extent" (Intellectual Powers, vi. 2).