ABSTRACT
Sections II.xxiii.6-14 of the Essay constitute a single argument in which Locke explicitly brought together three ingredients of his theory: his characterization of the idea of substance as the unknown cause of the union of coexisting qualities and powers, his intimation that there is a general corporeal substance or stuff common to all sensible things, and
his explanation of the secondary qualities and powers by which we chiefly distinguish the sorts of substances as due to the primary qualities of the minute parts of things. Towards the end of the passage there is something of a digression as Locke speculated on the reasons why God has not made the 'internal constitutions' of things open to our view, as perhaps they are open to the view of angels. The general purpose of the argument is clear enough, for it gives us all the ingredients necessary for the later distinction between real essence and nominal essence:
For our Senses failing us, in the discovery of the Bulk, Texture, and Figure of the minute parts of Bodies, on which their real Constitutions and Differences depend, we are fain to make use of their secondary Qualities, as the characteristical Notes and Marks, whereby to frame Ideas of them in our Minds, and distinguish them one from another.38
