The primary aim of this essay is to explain the central elements of Locke's theory of knowledge. A secondary aim arises from the official definition of knowledge introduced in the opening lines of book IV. Though Locke's repeated statements of the definition are consistent with the initial formulation, the consensus view among commentators is that that official definition is in tension with other book IV doctrines. My broader interpretation involves an effort to render the various doctrines consistent with the official (...) definition. The order of discussion: Section 1 explicates the definition of knowledge. Section 2 explains two main divisions of knowledge – namely, its three degrees, and the four sorts of knowable truths. In Section 3, I consider whether Locke understands knowable truths on a model of analyticity. Section 4 addresses potential problems about the objectivity of knowledge, given Locke's account. Section 5 focuses on external world knowledge – Locke calls this "sensitive knowledge" and it poses special difficulties for the official definition of knowledge. (shrink)