Locke's position with respect to ideas and our experience of the external world is sometimes labelled “representative realist” to indicate Locke's belief that our ideas represent their causes (hence “representative”) and that those ideas are faithful representatives that give us pictures which are as accurate as they can be – and as we need them to be – of the way the world really is (hence “realist”). Some commentators think that this rough sketch of Locke's position, when suitably refined and qualified, is reasonably correct. Others think it is, in differing ways, very far wide of the mark.

Rather than try to adjudicate in detail among the rivals, in what follows I shall try to give a survey of the main different readings and their supporting considerations. It may be that the best conclusion is that Locke, like many innovators, was better at starting promising new lines of approach than seeing and bearing in mind incompatibilities among those approaches. At any rate there is general agreement that Locke thinks ideas represent things in thought. But what are the things they represent, what does the representing and how is the representation accomplished?

We have seen that Descartes holds that his three kinds of ideas – innate, invented and adventitious – represent, respectively, (a) principles of reason and metaphysical truths, (b) imaginary items and fictions and (c) external sensible objects. And we have also seen that these three sorts of representation are all accomplished by what is the ultimate cause of each, namely God.