 Descartes and Berkeley treat attention very briefly, but each assigns attention to a particular explanatory role. Locke’s treatment of attention is also brief, but he has his own theory of the explanatory role that attention plays, and goes further than either Descartes or Berkeley in giving us a positive account of what attention is. His account is given as part of the catalogue of ‘Modes of Thinking’, which Locke sets out towards the beginning of Chapter Nineteen of Book Two of the Essay Concerning Human Understanding: