LOGIC (OF., Fr. logique, from Lat. logica, logics, from Gk. Xo-yuch [sc. r/xpn], foyik [se. teehm•, logic, logical [se. art], from X6-yos, logos, word, reason). Among the conscious processes treated by psychology (q.v.) are processes of thought. Psychology treats these processes as mental occurrences, and endeavors to ascertain the conditions under which they appear. But they are something more than mere occurrences. They have a peculiar character, which consists in the fact that they purport to be valid, and some of them are subsequently judged to be valid and others invalid. Both valid and invalid thought processes are of equal value to the psychologist, inasmuch as both are actual occurrences and equally demand scientific investigation as to the actual conditions under which they appear. Hence there is room for another science which in vestigates the differences between valid and in valid thinking and states the conditions to which thinking must conform in order that it may be valid. This science was called logic by the Stoics. There is another science which also deals with the validity of our thinking processes, along with the question of the validity of our knowl edge in general. This science is called episte mology, or the theory of knowledge (q.v.). Many thinkers, especially in recent years. have made no distinction between logic and epistemology, but it is perhaps better to use the word logic in the sense which it had for over two thousand years until the time of Kant, and to apply the term epistemology to the science which deals not with the question, In what, way must we think in order that our thought may be valid? but with the more fundamental questions, Is our knowl edge valid at all? And if so. What must be the relation of the knowing consciousness to the object known? Kant (q.v.) used logic in a larger sense. which made it include the treatment of this question of the relation of the knowing con sciousness to the known object. but he carefully distinguished the two meanings of the word. He thus recognized two kinds of logic, general and transcendental. General logic for Kant is the science which 'deals only with the pure form of thought,' i.e. only with the ways in which thought proceeds when it works correctly. Tran scendental logic sets forth 'the origin, the limits, and the objective validity of our pure con ceptions': i.e. it deal, with questions of episte
mology and of the philosophy of nature. Now adays it is the fashion, especially in Germany, to call the scientific treatment of such questions epistemological logic (German, erkenntnissthe oretische Logik). However. in this article the word will be limited to the science which treats merely of the norms or standards to which our thinking must conform if its results arc to be valid.
Taking for granted then that we can have knowledge which is really valid, the question which logic as treated here asks and tries to answer is, According to what standards must the thinking processes work in order that our knowl edge, so tar as it is gained by thought, may be valid knowledge? In other words, What are the laws of valid thinking? But this question cannot be answered until we have first ascertained the method by which these laws of" valid thought may be discovered. There are two theories on this subject, one which maintains that these laws are known a priori (q.v.), the other that they are known a posteriori. Thus we have a school of rationalistic logicians, and a school of experien tial logicians. Among the most pronounced ad vocates of rationalistic logic stand Wolff (q.v.) and Kant. The latter says of 'general logic' (practically logic as here treated) that "as pure logic. it has no empirical principle*. . . . Logic is a demonstrative science, and whatever it con tains must be certain entirely a priori" (Wat son's translation). Others, such as Mehl, maintain that these standards of correct thinking are discovered by experience. We think, and some of our thoughts prove valid. i.e. they lead us to results which are confirmed by all experi ence; others of our thoughts are not valid. i.e. subsequent experience does not confirm them. Now by examination, so it is claimed, we dis cover that valid thinking is characterized by certain features; it is all reducible to certain types. These types are the norms or laws of thought. Thus logical laws are on a par with physical laws. Physical laws are statements of the way in which physical bodies act. Logical laws are statements of the way in which correct thinking proceeds. It is only experience, this school asserts, which can reveal to us these laws.