To this reprint of Hume's Enquiry Concerning Human Understanding has been added a supplement containing se lections from his earlier and longer philosophical work, the Treatise on Human Understanding, referred to in the Author's Advertisement to 'the Enquiry (page xxvm., this edition). In spite of Hume's deprecatory reference to the Treatise, it remains the completest expression of his philosophical doctrine. The selected portions of the Treatise comprise (i) certain sections on causality which amplify the causal doctrine of the Enquiry and may profit ably be read after Section VII. Of the latter work; and (2) those sections which embody the essential features of Hume's constructive philosophy, his conception of matter and of self of spirit. Nothing in the Enquiry, with the exception of a few paragraphs of Section XII., corresponds to these sections of the Treatise. They should be read before or in place of, the comparatively irrelevant sections, IX-XI., of the Enquiry.