 Perhaps it is more profitable to ask whether, in his own terms, Locke ought to have accepted bare substratum. If we accept that the question of what binds together the qualities of a macroscopic object can be answered by appeal to the minute parts, the issue would then be what binds the primary qualities of atoms. Do the size, shape, mass, solidity of a particular atom require a bare substratum to inhere in for them to constitute a coherent object? Would they, without such a substratum be just a stack of qualities, a house of cards with nothing holding them together? There does not seem to be anywhere in the text where Locke discusses this problem—that is, the coherence of atoms as opposed to composite objects—explicitly. One possible resort is to treat solidity as the core or master quality and all the others as features of it. One would never ask what binds together a patch of colour and its shape, because the shape is the shape of the colour patch, and, though the shape of something can change, its shape cannot come away from it, like a separable component. Perhaps the shape, size and density of an atom are similarly features of the solidity. The quality solidity would then become equivalent to the notion of material stuff or material substance and Locke shows no sign of wanting to elide the ideas of quality and substance in this way, though it should be noted that this is what Descartes does with extension. Because he does not believe in void, extension carries with it the other basic properties of matter as features of it.