Hume Studies

109 HUME'S MISSING SHADE OF BLUE, INTERPRETED AS INVOLVING HABITUAL SPECTRA David Hume claimed that his hypothetical case of the unseen shade of blue posed no fundamental problem to his general empiricist principle. But I believe it well may show exactly what he denied it showed — viz. , that his empiricism rests on a mistake. Hume says: Suppose ... a person to have enjoyed his sight for thirty years, and to have become perfectly well acquainted with colours of all kinds, excepting 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 plac'd before him, descending gradually from the deepest to the lightest; 'tis 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 betwixt the contiguous colours, than in any other. Now I ask, whether 'tis possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, tho' it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can.... Sometimes one is surprised by the colour which emerges when one mixes paints, powders or lights of different hues, in the sense that one is unable to imagine this resulting colour until one actually sees it. I often have analogous experiences when sightreading music on the trombone. If there is a large, unfamiliar interval between the note I am playing and the one to be played next, so I cannot 'hear' the next note inwardly, I bring the slide to the correct position, set my lips at approximately the right tension, and presto! the correct note appears, despite 110 my inability to predict what it was going to sound like. Only after I have heard it can I also 'hear' it, i.e, predict its occurrence in this melodic line. Cases like these are not puzzling philosophically, because in them, the note, colour, etc. arises primarily from the equipment used — e.g. , paints, powders or lights, the trombone and tension of the lips, and so on — rather than from the mind of the person who uses these things. But in Hume's example, no extra-mental objects or events play a direct role in creating the imagined colour. In fact, this colour never appears at all outside the subject's mind, and he never sees it. Therefore here the imagined colour is produced entirely by the subject himself, without his having copied it from anything in the external world. Yet this contradicts the maxim Hume laid down at the beginning of the Treatise that all simple ideas arise from correspondingly simple (sense) impressions. Two points perhaps mitigate the seriousness of the problem set by the missing shade of blue. First, Hume saw clearly, as Locke did not, that "innate" does 2 not mean the same as "justified." He was not so much concerned with the question of where ideas come from, as with how these ideas can be shown to be legitimate. His answer to the latter question is that experience alone is competent to show this. Second, strictly speaking, no idea is itself a piece of knowledge, but only something with the help of which one constructs knowledge-claims; and it is necessary for a person to justify knowledge-claims which are composed of innate ideas, by checking them against experience, just as much as knowledge-claims composed of non-innate materials. For example, suppose I possess innately the idea (visual image) of blue and the idea (tactile image) of cool. To say that these ideas are innate means that they are merely triggered or activated in my Ill mind by experiences I happen to have, but are not created by these experiences, and are not necessarily copies of them. Nevertheless, in order for me to know something which involves these ideas, I first must put them together in a judgment, and then confirm that judgment by appeal to experience. For instance, I might use these ideas to make the judgment...