This boundless multitude of ideas, through which our mind can rove, surely has no spatial extension. But because of the necessity of conceiving any multitude as existing in some kind of space, it was thought proper to posit an ideal space in addition to the physical one. In other words, metaphorical dimensions were added to dimensions properly so called. But whether spatially or not, we strive to conceive ideas as many, each one of them existing by itself, and susceptible of being thought independently of the others. In reality however we never succeed in thinking them except as bound together and forming a system, in such a way that no single one of them can be thought except by thinking the others with it. Take man as an instance: each one of us has intuitively the idea of man, but this idea is not possessed like a word of which we may not even know the meaning. In thinking the idea we must think something which is its content. If we know what man is, we must be able to attribute a content to the idea of man. We may say, as the ancients did, that man is the laughing animal, or the speaking animal, because he is the only animal capable of expressing the emotions of his soul by laughter or by the inflection of his voice; because, in other words, he is the only animal who is conscious of what goes on within him. Or perhaps we might say that man is the reasoning animal, and we think this idea when we have thought the idea of _animal_ and the idea of _reason_. But can the idea of animal be thought by itself alone? It, as well as the idea of reason, must have a content; that is, each must be connected with other ideas, without which it would be deprived of all consistency. And so the mind that begins to think one single idea is compelled, almost dragged, to pass on to another, then to a third, and so on indefinitely. It finds itself in the condition of the man who tried to grasp a single link of a chain, just one, and found that he could not have it except on condition of taking the whole chain. So it is with ideas. We may not be capable of encompassing all of them in one single thought; but whenever we try to fix any one of them in our mind, it presents itself to us as a knot in which many other ideas are interlaced, twisted, and entangled. They form an infinite chain, in which it is not possible to think the first link or the last one, because the beginning is welded to the end, and we turn and turn and never reach the last. Is not this the nature of the ideas as we see them, as they constitute the field from which we must harvest all our possible thoughts?