ESSAY ON THE HUMAN UNDER STANDING, An. John Locke's on the Human Understanding> is the classic of Eng lish common sense empiricism. Subsequent philosophy and psychology and English thought. in general are weighted with its terminology and opinions.
Locke's purpose, so he tells us, was °to in quire into the origin, certainty and extent of human knowledge, together with the grounds and degrees of belief, opinion and assent?) He would determine the powers of the understand ing by an method, that is, by trac ing the growth of knowledge in the individual. As a result of his analysis Locke decided that mind is conversant only with °ideas') and their relations, which ideas it acquired through sen sation and through reflection on its own oper ations. These ideas. °whatever is the object of the mind when a man thinks," are the copies of things—the effects produced in us by ob jects. He never questioned their representa tive character so far as the primary qualities, such as extension, motion, etc., are concerned and considered them sufficient evidence of an external world.
Knowledge is the perception of the agree ment or disagreement of ideas and arises in three degrees : intuitive, by which we perceive immediately the relation between two ideas; demonstrative, i.e., a chain of intuitions ; sensi
tive, which gives us knowledge of particular things. The limitation thus imposed leaves out side the realm of knowledge most of the mat ters with which the mind is generally occupied in the conduct of life. These must be deter mined by probable °judgment? Locke was very uncritical and avoided the logical extremes to which his argument is ob viously subject and which are to be found in the idealism of Berkeley and the sensationalism of Condillac. His doctrine of representative ideas as the ultimate data of knowledge clearly expresses an epistemological position which may be regarded as the fundamental principle or fundamental fallacy of subsequent philosophy, according to one's metaphysical preferences.
The (Essay> has probably run to more edi tions than any other modem philosopical classic and almost every subsequent philosopher has taken it at one time or another as a topic. Leib nitz's 'Nouveaux Essais sur l'entendement hu main> (1761) is a running commentary on Locke. The best critical edition is that by Prof. C. Fraser (1894).