Page:On the Fourfold Root, and On the Will in Nature.djvu/86

 consciously performed actions of all animals. The medium for motives is knowledge : an intellect is accordingly needed for susceptibility to motives. The true characteristic of the animal is therefore the faculty of knowing, of representing (Das Vorstellen). Animals, as such, always move towards some aim and end, which therefore must have been recognised by them : that is to say, it must have presented itself to them as something different from themselves, yet of which they are conscious. Therefore the proper definition of the animal would be : That which knows ; for no other definition quite hits the mark or can even perhaps stand the test of investigation. Movement induced by motives is necessarily wanting where there is no cognitive faculty, and movement by stimuli alone remains, i.e. plant life. Irritability and sensibility are therefore inseparable. Still motives evidently act in a different way from stimuli ; for the action of the former may be very brief, nay, need only be momentary; since their efficacy, unlike that of stimuli, stands in no relation whatever to the duration of that action, to the proximity of the object, &c. &c. A motive needs but to be perceived therefore, to take effect ; whereas stimuli always require outward, often even inward, contact and invariably a certain length of time.

This short sketch of the three forms of causality will suffice here. They are more fully described in my Prize-essay on Free Will. One thing, however, still remains to be urged. The difference between cause, stimulus, and motive, is obviously only a consequence of the various degrees of receptivity of beings ; the greater their receptivity, the feebler may be the nature of the influence : a stone needs an impact, while man obeys a look. Nevertheless, both are moved by a sufficient cause, therefore with the