Accordingly, just as if a finger be pressed under the eyeball without being observed, one object will not only present two visual images, but will create an opinion of its being two objects; while if it be observed, the presentation will be the same, but the same opinion will not be formed of it; exactly so it is in states of sleep: if the sleeper perceives that he is asleep, and is conscious of the sleeping state during which the perception comes before his mind, it presents itself still, but something within him speaks to this effect: 'the image of Coriscus presents itself, but the real Coriscus is not present'; for often, when one is asleep, there is something in the soul which declares that what then presents itself is but a dream.