Is it difficult to discover that our ideas proceed only from our senses? that the things we look on as real and existing are those of which our senses have always rendered us the same testimony? that those which we conceive to have certain existence are those which ever present themselves in the same order? that consequently our ideas, very far from being the causes of things, are only effects, and so far from resembling particular things, become less similar to the objects as they are more general; that at length our mental abstractions are only negative beings, which do not exist even intellectually but by the retrenchment which we make of sensible qualities to real beings. From hence is it not plain that abstractions can never become principles, neither of existence nor real knowledge? on the contrary, our knowledge can only proceed from the results of properly comparing our sensations. These results are what is termed _experience_, the sole source of all real science. The adoption of every other principle is an abuse, and every edifice built on abstracted ideas is a temple founded on error. Error bears a much more extended signification in philosophy than in morality: in morals a thing may be false, only because it is misrepresented. Metaphysical falsehood consists not in misrepresentation alone, but in crediting that which has no existence, and even in not being of any mode whatever. It is in this kind of error, of the first order, that the Platonists, the Sceptics, and the Egotists have fallen into, their false suppositions have obscured the natural light of truth, clouded reason, and retarded the advancement of philosophy.