 Locke has an atomic or perhaps more accurately a corpuscular theory of  ideas.[4]  There is, that is to say, an analogy between the way atoms or corpuscles combine into complexes to form physical objects and the way ideas combine. Ideas are either simple or complex. We cannot create simple ideas, we can only get them from experience. In this respect the mind is passive. Once the mind has a store of simple ideas, it can combine them into complex ideas of a variety of kinds. In this respect the mind is active. Thus, Locke subscribes to a version of the empiricist axiom that there is nothing in the intellect that was not previously in the senses—where the senses are broadened to include reflection. Book III deals with the nature of language, its connections with ideas and its role in knowledge. Book IV, the culmination of the previous reflections, explains the nature and limits of knowledge, probability, and the relation of reason and faith. Let us now consider the Essay in some detail.