For one who holds that the whole perceptual world is only an ideal world, and, moreover, the effect of things unknown to him acting on his soul, the real problem of knowledge is naturally concerned, not with the ideas present only in the soul, but with the things which lie outside his consciousness, and which are independent of him. He asks, How much can we learn about them indirectly, seeing that we cannot observe them directly? From this point of view, he is concerned, not with the connection of his conscious percepts with one another, but with their causes which transcend his consciousness and exist independently of him, whereas the percepts, on his view, disappear as soon as he turns his sense-organs away from the things themselves. Our consciousness, on this view, works like a mirror from which the pictures of definite things disappear the very moment its reflecting surface is not turned towards them. If, now, we do not see the things themselves, but only their reflections, we must obtain knowledge of the nature of the former indirectly by drawing conclusions from the character of the latter. The whole of modern science adopts this point of view, when it uses percepts only as a means of obtaining information about the motions of matter which lie behind them, and which alone really "are." If the philosopher, as Critical Idealist, admits real existence at all, then his sole aim is to gain knowledge of this real existence indirectly by means of his ideas. His interest ignores the subjective world of ideas, and pursues instead the causes of these ideas. The Critical Idealist can, however, go even further and say, I am confined to the world of my own ideas and cannot escape from it. If I conceive a thing beyond my ideas, this concept, once more, is nothing but my idea. An Idealist of this type will either deny the thing-in-itself entirely or, at any rate, assert that it has no significance for human minds, i.e., that it is as good as non-existent since we can know nothing of it.