Keith Allen

What, according to Locke, are ideas? I argue that Locke does not give an account of the nature of ideas. In the Essay, the question is simply set to one side, as recommended by the “Historical, plain Method” that Locke employs. This is exemplified by his characterization of ‘ideas’ in E I.i.8, and the discussion of the inverted spectrum hypothesis in E II.xxxii. In this respect, Locke's attitude towards the nature of ideas in the Essay is reminiscent of Boyle's diffident attitude towards the nature of matter. In posthumously published work, however, Locke suggests that the enquiry into the nature of ideas is one of the things that the enquiry into the extent of human knowledge undertaken in the Essay actually shows to lie beyond the “compass of human understanding”. In this respect, Locke's attitude towards the nature of ideas is reminiscent of Sydenham's attitude towards the nature of diseases.

Objects appear different as the illumination under which they are perceived varies. This fact is sometimes thought to pose a problem for the view that colours are mind-independent properties: if a coloured object appears different under different illuminations, then under which illumination does the object appear the colour it really is? I argue that given the nature of natural daylight, and certain plausible assumptions about the nature of the colours it illuminates, there is a non-arbitrary reason to suppose that it is under natural daylight that we are able to perceive the real colours of objects.

What are hallucinations? A common view in the philosophical literature is that hallucinations are degenerate kinds of perceptual experience. I argue instead that hallucinations are degenerate kinds of sensory imagination. As well as providing a good account of many actual cases of hallucination, the view that hallucination is a kind of imagination represents a promising account of hallucination from the perspective of a disjunctivist theory of perception like naïve realism. This is because it provides a way of giving a positive characterisation of hallucination—rather than characterising hallucinations in negative, relational, terms as mental events that are subjectively indistinguishable from veridical perceptual experiences