In the realm of facts and of experience such operations would necessarily be limited by the resistance of matter and the uncompromising character of physical laws. In the purely intellectual domain they are subject to logic; but logic itself being an intellectual fabric, its indulgence is almost unlimited. In truth, the association and the disassociation of ideas (or of images, for the idea is merely a worn-out image) pursue a winding course which it is impossible to determine, and whose general direction, even, it is difficult to follow. There are no ideas so remote, no images so ill-assorted, that an easy habit of association cannot bring them together, at least, momentarily. Victor Hugo, seeing a cable wrapped with rags at the point where it crossed a sharp ridge, saw, at the same time, the knees of tragic actresses padded to break the dramatic falls in the fifth act;[1] and these two things so remote--a rope anchored on a rock, and the knees of an actress--are evoked, as we read, in a parallel which takes our fancy because the knees and the rope are equally "furred,"[2] the first above and the latter below, at the bend; because the elbow made by a cable thus cast bears a certain resemblance to a leg that is bent; because Giliatt's situation is quite tragic; and, finally, because, even while perceiving the logic of these comparisons, we perceive, no less clearly, their delicious absurdity. Such an association is perforce extremely fugitive, unless the language adopts it and makes of it one of those figures of speech with which it delights to enrich itself. It should occasion no surprise were this bend of a cable to be called its "knee." In any event, the two images remain ever ready to be divorced, divorce being the permanent rule in the world of ideas, which is the world of free love. This fact sometimes scandalizes simple folk. Whoever first dared to say the "mouth" or the "jaw" of a cannon, according to which of those terms is the older, was, without doubt, accused either of preciousness or of coarseness. If it be improper to speak of the "knee" of a rope, it is quite proper to speak of the "elbow" of a pipe or the "paunch" of a bottle. But these examples are presented merely as elementary types of a mechanism which is more familiar to us in practice than in theory. Leaving aside all images still living, we shall concern ourselves exclusively with ideas--that is to say, those tenacious and fugitive shades which flutter about eternally bewildered in men's brains.