However, Hume admits that there is one objection to his account: the problem of ""The Missing Shade of Blue"". In this thought-experiment, he asks us to imagine a man who has experienced every shade of blue except for one (see Fig. 1). He predicts that this man will be able to divine the color of this particular shade of blue, despite the fact that he has never experienced it. This seems to pose a serious problem for the empirical account, though Hume brushes it aside as an exceptional case by stating that one may experience a novel idea that itself is derived from combinations of previous impressions. (Hume 1974:319)