 Without objecting to this account of the semantics of names of SQs, we can add that the doctrine of SQs solves an epistemic problem arising from Locke’s thesis that the limited knowledge we have is sufficient for our needs (E 1.5). The solution to this problem is in part about the world. Jacovides overlooks Locke’s semantic theory of simple ideas of sensation in general and its function in his epistemology. The key texts are Essay 2.30.1–2, 2.31.1–2. and 4.4.4. In outline, God sustains steady causal connections among the different internal constitutions of bodies, the constitutions of the bodies of perceivers, and all the simple ideas of sensation that enter their minds. With this foundation in place, the fact, as Locke has it, that we are aware that simple ideas of sensation come from without us enables these ideas to be, and be taken to be, reliable signs of things that are founded in reality (E 2.30.2, 31.2; 4.4.4); for a defense of the natural sign interpretation of simple ideas of sensation, see Ayers 1991: 60–64. Ideas of SQs, in particular, are not ideas of micro-constitutions; they do not inform us of the nature of what they represent. They are ideas of powers that stand in for the causal foundations that underwrite sense perception; see Ayers 1997 on the place-holder function of this idea of power. We cannot have perceptual knowledge of the nature of the foundations. But because ideas of SQs track collections of PQ of insensible particles on which the ideas depend, we have the cogntiive ability to distinguish different objects we have to do with, discern their qualities, and take them for our needs (E 2.30.3; 4.4.4).