But in the last instance, or in the secret of our inner being, what sets in activity the association of thought itself, the laws of which were set forth above, is the _will_, which urges its servant the intellect, according to the measure of its powers, to link thought to thought, to recall the similar, the contemporaneous, to recognise reasons and consequents. For it is to the interest of the will that, in general, one should think, so that one may be well equipped for all cases that may arise. Therefore the form of the principle of sufficient reason which governs the association of thoughts and keeps it active is ultimately the law of motivation. For that which rules the sensorium, and determines it to follow the analogy or other association of thoughts in this or that direction, is the will of the thinking subject. Now just as here the laws of the connection of ideas subsist only upon the basis of the will, so also in the real world the causal connection of bodies really subsists only upon the basis of the will, which manifests itself in the phenomena of this world. On this account the explanation from causes is never absolute and exhaustive, but leads back to forces of nature as their condition, and the inner being of the latter is just the will as thing in itself. In saying this, however, I have certainly anticipated the following book. But because now the _outward_ (sensible) occasions of the presence of our ideas, just as well as the _inner_ occasions (those of association), and both independently of each other, constantly affect the consciousness, there arise from this the frequent interruptions of our course of thought, which introduce a certain cutting up and confusion of our thinking. This belongs to its imperfections which cannot be explained away, and which we shall now consider in a separate chapter. Chapter XV. On The Essential Imperfections Of The Intellect.