THE ORIGIN AND FORMATION OF IDEAS
§ 1 . The ground having been cleared by the refutation of the Theory of Innate Principles, which Locke regarded as the basis of the only theory of knowledge fundamentally opposed to his own, the way would seem to be open for a direct attack upon the main problem of the Essay, the determination of the nature and extent of human knowledge or certainty. Instead of making such an attempt, however, Locke proceeds, in his Second Book, to discuss at considerable length certain questions concerning our ideas, the consideration of which he regards as an essential preliminary to the solution of the problem of knowledge.
That ideas cannot of themselves constitute knowledge, Locke is perfectly aware. The unit of knowledge, he maintains, is the proposition or judgment, which is alone capable of being true or false. When, contrary to strict propriety, ideas are spoken of as true or false, it is always, he points out, in virtue of some secret or tacit proposition, in which an affirmation or denial is made1. But if ideas, taken as such, fall short of the requirements of knowledge, it is also true that apart from ideas there can be no knowledge. Although certainty cannot be 'placed in any one single idea, simple or complex,' it must be 'grounded on ideas2.' Ideas form, indeed, 'the materials of knowledge,'____________________