Ideas play at least two roles in Locke's theory of the understanding. They are constituents of ‘propositions,’ and some of them ‘represent’ the qualities and sorts of surrounding bodies. I argue that each role involves a distinct kind of intentional directedness. The same idea will in general be an ‘idea of’ two different objects, in different senses of the expression. Identifying Locke's scheme of twofold ‘ofness’ reveals a common structure to his accounts of simple ideas and complex ideas of substances. A consequence is a distinction among substance sorts parallel to one of his distinctions between primary and secondary qualities.