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 two monographs (Enquiry Concerning Human Understanding and Enquiry Concerning the Principles of Morals) in which the most important problems of his masterpiece are presented in briefer form. He treats the problems of religion from the historico-psychological viewpoint in his Natural History of Religion (1757). The Dialogues on Natural Religion, written in 1751, but not published until after his death, are a critical study of the problem of religion. After having held several public offices, Hume spent his last years at Edinboro in scholarly retirement.

Whilst Locke made a sharp distinction between the problem concerning the origin of our ideas and that of their validity, for Hume the two problems, so far as they pertain to ideas in the more restricted sense (ideas as distinguished from perceptions or impressions, i. e. sensations), are identical. He starts with the assumption that an idea can be valid only when it is based on a sensation (perception, impression). He makes no investigation into the origin of sensations because this problem has no epistemological significance: the question whether they proceed from external objects or from God or from the innate powers of the mind has no bearing on the problem of their validity. Hume likewise excludes that division of knowledge which is wholly confined to the matter of defining and developing the relations of our ideas—pure logic and mathematics—from his critical investigations entirely. The sole problem of his investigations pertains to the validity of the ideas by means of which we presume to be justified in assuming knowledge beyond what is given in sense-perceptions. The problem growing out of the application of mathematics to empirical science was not formulated until later. This was done by Kant on the basis of his studies of Newton.