 Throughout the Essay, Locke discusses real essences, internal constitutions and substratum, and getting clear on each concept is required in order to produce a consistent and accurate interpretation of Locke on real essences. While it is not possible to do justice to any of the subjects here, it is important to give some background before proceeding. When Locke defines the ‘real essence’, he often describes it as “that Constitution, whereon the Properties of these several things depended” (III.iii.19). On occasion he even connects internal constitutions with essences as if they were synonymous: “[collections of simple ideas] are therefore supposed to flow from the particular internal Constitution, or unknown Essence of that Substance” (II.xxiii.3). Similarly, the concept of ‘substance’ or ‘substratum’, i.e., pure substance in general, is conceived as an underlying ‘thing’ which supports, or upholds, the properties of bodies: