It is not upon causality proper, but upon the identity of the knowing with the willing Subject, as shown in § 42, that the influence is based, which the will exercises over the intellect, when it obliges it to repeat representations that have once been present to it, and in general to turn its attention in this or that direction and evoke at pleasure any particular series of thoughts. And even in this, the will is determined by the law of motives, in accordance with which it also secretly rules what is called the association of ideas, to which I have devoted a separate chapter (the 14th) in the second volume of my chief work. This association of ideas is itself nothing but the application of the Principle of Sufficient Reason in its four forms to the subjective train of thought; that is, to the presence of representations in our consciousness. But it is the will of the individual that sets the whole mechanism in motion, by urging the intellect, in accordance with the interest, _i.e._, the individual aims, of the person, to recall, together with its present representations, those which either logically or analogically, or by proximity in Time or Space, are nearly related to them. The will's activity in this, however, is so immediate, that in most cases we have no clear consciousness of it; and so rapid, that we are at times even unconscious of the occasion which has thus called forth a representation. In such cases, it appears as if something had come into our consciousness quite independently of all connection with anything else; that this, however, is impossible, is precisely the Root of the Principle of Sufficient Reason, which has been fully explained in the above-mentioned chapter of my chief work.[155] Every picture which suddenly presents itself to our imagination, every judgment even that does not follow its previously present reason, must be called forth by an act of volition having a motive; although that motive may often escape our perception owing to its insignificance, and although such acts of volition are often in like manner unperceived, because they take place so easily, that wish and fulfilment are simultaneous. [155] See "Die Welt, a. W. u. V." vol. ii. ch. xiv. § 45. _Memory._