Constructivism versus Realism in Leibniz's Confrontation with Locke

Leibniz’s general concern in contrasting the conventionalist drift of Locke’s Essay could hide to the reader a common background of assumptions and problems, that, roughly speaking, is determined by the crisis of the ancient image of reality as a hierarchical order of essences. Leibniz and Locke also share the assumption, derived from the nominalistic tradition, that only individuals do exist. I shall try to show briefly this tendency in Leibniz’s own accounts of species and classifications before his confrontation with Locke. When faced with Locke’s attitude in the Essay, however, he will be more eager to contrast an excessive weakening of the ontological import of our partition of the world. To show this, I shall first consider a fundamental distinction drawn by Locke between ‘modes’, on one hand, and substances on the other hand. According to Locke, the latter presuppose a real archetype, and are in principle inadequate; although our ‘ideas’ of substances imply a constructivist aspect, they must obey strong empirical constraints. On the contrary modes, the ‘archetypes’ of which lie in our mind, allow a full constructivist approach. Locke’s fundamental dichotomy can remind to present-day readers the contrast, frequently proposed in contemporay debates, between natural and social objects.