How are individual substances related to their qualities, and ultimately to the qualitative manifold? Anticipating the transition from Leibniz's early discussion in the Disputatio to his mature account of simple individual substances, we noted at the close of chapter 1 that it is in connection with Leibniz's answer to these questions that his metaphysic becomes maximally difficult. The issue of relational properties (chapter 2), perplexing enough in its own right, is just one – albeit crucial – thread in a larger web that is Leibniz's answer. At the center of Leibniz's answer is the complete concept doctrine, from which emerge various modal strands intersecting other parts of the Leibnizian metaphysic. The greatest tension is focused at their intersection with our workaday modal claims about individuals, and with the dominant themes in Leibniz's account of individuation – the requirement of separability or independence for individual substances, and the requirement that whatever individuates a substance must be wholly internal to it. Suppose that individual concepts are indeed complete in their specification of the properties enjoyed by each substance; and suppose, as Leibniz seems clearly to hold, that no substance could have a complete concept different from the one it in fact has – complete concepts in some sense “defining” possible substances. The resulting de re modal constraints on the relation between any substance and its qualitative clothing would look to imply that no substance could have properties other than those it in fact has.