Even useless things take a form in the mind, as everything has a form. But it has a form akin to the source of impression. For instance, not only a painting, a picture, has a perceptible form; music also is a language; the eyes do not see it, but the ears see it. So the mind even accumulates all such forms as sour, sweet, bitter, pungent, all the different tastes. We do not see them, but they are registered in the mind in a form distinguished by us. The eyes do not see the form, but the mind sees it actually in the same way as we had once tasted it. To the mind all these forms are intelligible in the same way, exactly the same as when they come through the different senses.