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"The Missing Shade of Blue" is an example introduced by the Scottish philosopher David Hume to show that it is at least conceivable that the mind can generate an idea without first being exposed to the relevant sensory experience. It is regarded as a problem by philosophers because it appears to stand in direct contradiction to what Hume had just written. ==The source of the problem== In both ''A Treatise of Human Nature'' and ''An Enquiry Concerning Human Understanding'', philosopher David Hume argues that all perceptions of the mind can be classed as either 'Impressions' or 'Ideas'. He further argues that: ::"We shall always find, that every idea which we examine is copied from a similar impression. Those who would assert, that this position is not universally true nor without exception, have only one, and at that an easy method of refuting it; by producing that idea, which, in their opinion, is not derived from this source."〔''Enquiries'', Section II. Of the Origin of Ideas〕 The problem of the ''missing shade of blue'' arises because just two paragraphs later Hume seems to provide just such an idea. He says: ::"There is, however, one contradictory phenomenon, which may prove, that it is not absolutely impossible for ideas to arise, independent of their correspondent impressions. I believe it will readily be allowed, that the several distinct ideas of colour, which enter by the eye, or those of sound, which are conveyed by the ear, are really different from each other; though, at the same time, resembling. Now if this be true of different colours, it must be no less so of the different shades of the same colour; and each shade produces a distinct idea, independent of the rest. For if this should be denied, it is possible, by the continual gradation of shades, to run a colour insensibly into what is most remote from it; and if you will not allow any of the means to be different, you cannot, without absurdity, deny the extremes to be the same. Suppose, therefore, a person to have enjoyed his sight for thirty years, and to have become perfectly acquainted with colours of all kinds, except one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the different shades of that colour, except that single one, be placed before him, descending gradually from the deepest to the lightest; it is plain, that he will perceive a blank, where that shade is wanting, and will be sensible, that there is a greater distance in that place between the contiguous colours than in any other. Now I ask, whether it be possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, though it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can: And this may serve as a proof, that the simple ideas are not always, in every instance, derived from the correspondent impressions; though this instance is so singular, that it is scarcely worth our observing, and does not merit, that for it alone we should alter our general maxim.""〔''Enquiries'', Section II. Of the Origin of Ideas〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「The Missing Shade of Blue」の詳細全文を読む スポンサード リンク
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