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Since Descartes, philosophers have assumed that all ideas (Greek, ‘look’, ‘form’ or ‘kind’) are ‘in’ the mind. Some philosophers, such as Locke and Hume, seem to have thought that all ideas are sensory images. Whenever one perceives, remembers, thinks, imagines or dreams one has a sensory image ‘before’ one\'s mind. When one thinks of a cat, for example, one has a visual image similar to, though somewhat less vivid than, the visual image one has when one sees a cat. One problem here is this: if all ideas are sensory images, how can one have an abstract idea, an idea not of this or that particular cat, but of ‘cat’ in general? A sensory image of a cat is inevitably an image of a cat with some determinate colour and size, and how can an image of a cat with some determinate colour and size serve as our general idea of ‘cat’, when cats come in a variety of shapes and colours?
Contemporary philosophers insist that thinking of a cat need not involve having a mental picture or sensory image of a cat similar to the image one has when one perceives a cat. This seems right. But if having an idea is not a matter of having a sensory image before the mind, what is it to have an idea? Some hold that one possesses the idea ‘cat’ if one can distinguish cats from things which are not cats. One problem for this suggestion is that there are machines which can distinguish between damaged and undamaged tins of beans—machines which will throw out the damaged cans. But such machines seem not to have minds or ideas. AJ
Further reading J.C. Mackie, Problems from Locke; Wittgenstein, The Blue and Brown Books. |
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