 Since Berkeley, Locke’s doctrine of the substratum or substance in general has been attacked as incoherent. It seems to imply that we have a particular without any properties, and this seems like a notion that is inconsistent with empiricism. We have no experience of such an entity and so no way to derive such an idea from experience. Locke himself acknowledges this point (I.4.18, N: 95). In order to avoid this problem, Michael Ayers has proposed that we must understand the notions of ‘substratum’ and ‘substance in general’ in terms of Locke’s distinction between real and nominal essences and particularly his doctrine of real essences developed in Book III of the Essay rather than as a separate problem from that of knowing real essences. The real essence of a material thing is its atomic constitution. This atomic constitution is the causal basis of all the observable properties of the thing, from which we create nominal essences. Were the real essence known, all the observable properties could be deduced from it. Locke claims that the real essences of material things are quite unknown to us. Locke’s concept of substance in general is also a ‘something I know not what’. Thus, on Ayers’ interpretation ‘substance in general’ means something like ‘whatever it is that supports qualities’ while the real essence means ‘this particular atomic constitution that explains this set of observable qualities’. Thus, Ayers wants to treat the unknown substratum as picking out the same thing as the real essence—thus eliminating the need for particulars without properties. This proposed way of interpreting Locke has been criticized by scholars both because of a lack of textural support, and on the stronger grounds that it conflicts with some things that Locke does say (see Jolley 1999: 71–3). As we have reached one of the important concepts in Book III, let us turn to that Book and Locke’s discussion of language.