THE STREAM OF THOUGHT. 231 And the view of these philosopliers has been called little into question, for our common experience seems at first sight to corroborate it entirely. Are not the sensations we get from the same object, for example, always the same ? Does not the same piano-key, struck with the same force, make us hear in the same way ? Does not the same grass give us the same feeling of green, the same sky the same feeling of blue, and do we not get the same olfactory sen- sation no matter how many times we put our nose to the same flask of cologne ? It seems a piece of metaphysical sophistry to suggest that we do not; and yet a close at- tention to the matter shows that there is no proof that the same bodily sensation is ever got by tcs tivice. What is got tivice is the same object. We hear the same note over and over again ; we see the same quality of green, or smell the same objective perfume, or experience the same species of pain. The realities, concrete and abstract, physi- cal and ideal, whose permanent existence we believe in, seem to be constantly coming up again before our thought, and lead us, in our carelessness, to suppose that our ' ideas ' of them are the same ideas. When we come, some time later, to the chapter on Perception, we shall see how invet- erate is our habit of not attending to sensations as subjec- tive facts, but of simply using them as stepping-stones to pass over to the recognition of the realities whose presence they reveal. The grass out of the window now looks to me of the same green in the sun as in the shade, and yet a painter would have to paint one part of it dark brown, arother part bright yellow, to give its real sensational eifect. We take no heed, as a rule, of the different way in which the same things look and sound and smell at different dis- tances and under different circumstances. The samenes'^? of the things is what we are concerned to ascertain ; and any sensations that assure us of that will probably be con- sidered in a rough way to be the same witfi each other. This is what makes off-hand testimony about the subjective identity of different sensations well-nigh worthless as a proof of the fact. The entire history of Sensation is a com^ mentary on our inability to tell whether two sensations received apart are exactly alike. What appeals to our
