The uncaused nature of will has been actually recognised, where it manifests itself most distinctly, as the will of man, and this has been called free, independent. But on account of the uncaused nature of the will itself, the necessity to which its manifestation is everywhere subjected has been overlooked, and actions are treated as free, which they are not. For every individual action follows with strict necessity from the effect of the motive upon the character. All necessity is, as we have already said, the relation of the consequent to the reason, and nothing more. The principle of sufficient reason is the universal form of all phenomena, and man in his action must be subordinated to it like every other phenomenon. But because in self-consciousness the will is known directly and in itself, in this consciousness lies also the consciousness of freedom. The fact is, however, overlooked that the individual, the person, is not will as a thing-in-itself, but is a phenomenon of will, is already determined as such, and has come under the form of the phenomenal, the principle of sufficient reason. Hence arises the strange fact that every one believes himself a priori to be perfectly free, even in his individual actions, and thinks that at every moment he can commence another manner of life, which just means that he can become another person. But a posteriori, through experience, he finds to his astonishment that he is not free, but subjected to necessity; that in spite of all his resolutions and reflections he does not change his conduct, and that from the beginning of his life to the end of it, he must carry out the very character which he himself condemns, and as it were play the part he has undertaken to the end. I cannot pursue this subject further at present, for it belongs, as ethical, to another part of this work. In the meantime, I only wish to point out here that the phenomenon of the will which in itself is uncaused, is yet as such subordinated to the law of necessity, that is, the principle of sufficient reason, so that in the necessity with which the phenomena of nature follow each other, we may find nothing to hinder us from recognising in them the manifestations of will.
Only those changes which have no other ground than a motive, i.e., an idea, have hitherto been regarded as manifestations of will. Therefore in nature a will has only been attributed to man, or at the most to animals; for knowledge, the idea, is of course, as I have said elsewhere, the true and exclusive characteristic of animal life. But that the will is also active where no knowledge guides it, we see at once in the instinct and the mechanical skill of animals.31 That they have ideas and knowledge is here not to the point, for the end towards which they strive as definitely as if it were a known motive, is yet entirely unknown to them. Therefore in such cases their action takes place without motive, is not guided by the idea, and shows us first and most distinctly how the will may be active entirely without knowledge. The bird of a year old has no idea of the eggs for which it builds a nest; the young spider has no idea of the prey for which it spins a web; nor has the ant-lion any idea of the ants for which he digs a trench for the first time. The larva of the stag-beetle makes the hole in the wood, in which it is to await its metamorphosis, twice as big if it is going to be a male beetle as if it is going to be a female, so that if it is a male there may be room for the horns, of which, however, it has no idea. In such actions of these creatures the will is clearly operative as in their other actions, but it is in blind activity, which is indeed accompanied by knowledge but not guided by it. If now we have once gained insight into the fact, that idea as motive is not a necessary and essential condition of the activity of the will, we shall more easily recognise the activity of will where it is less apparent. For example, we shall see that the house of the snail is no more made by a will which is foreign to the snail itself, than the house which we build is produced through another will than our own; but we shall recognise in both houses the work of a will which objectifies itself in both the phenomena—a will which works in us according to motives, but in the snail still blindly as formative impulse directed outwards. In us also the same will is in many ways only blindly active: in all the functions of our body which are not guided by knowledge, in all its vital and vegetative processes, digestion, circulation, secretion, growth, reproduction. Not only the actions of the body, but the whole body itself is, as we have shown above, phenomenon of the will, objectified will, concrete will. All that goes on in it must therefore proceed through will, although here this will is not guided by knowledge, but acts blindly according to causes, which in this case are called stimuli.
I call a cause, in the narrowest sense of the word, that state of matter, which, while it introduces another state with necessity, yet suffers just as great a change itself as that which it causes; which is expressed in the rule, “action and reaction are equal.” Further, in the case of what is properly speaking a cause, the effect increases directly in proportion to the cause, and therefore also the reaction. So that, if once the mode of operation be known, the degree of the effect may be measured and calculated from the degree of the intensity of the cause; and conversely the degree of the intensity of the cause may be calculated from the degree of the effect. Such causes, properly so called, operate in all the phenomena of mechanics, chemistry, and so forth; in short, in all the changes of unorganised bodies. On the other hand, I call a stimulus, such a cause as sustains no reaction proportional to its effect, and the intensity of which does not vary directly in proportion to the intensity of its effect, so that the effect cannot be measured by it. On the contrary, a small increase of the stimulus may cause a very great increase of the effect, or conversely, it may eliminate the previous effect altogether, and so forth. All effects upon organised bodies as such are of this kind. All properly organic and vegetative changes of the animal body must therefore be referred to stimuli, not to mere causes. But the stimulus, like every cause and motive generally, never determines more than the point of time and space at which the manifestation of every force is to take place, and does not determine the inner nature of the force itself which is manifested. This inner nature we know, from our previous investigation, is will, to which therefore we ascribe both the unconscious and the conscious changes of the body. The stimulus holds the mean, forms the transition between the motive, which is causality accompanied throughout by knowledge, and the cause in the narrowest sense. In particular cases it is sometimes nearer a motive, sometimes nearer a cause, but yet it can always be distinguished from both. Thus, for example, the rising of the sap in a plant follows upon stimuli, and cannot be explained from mere causes, according to the laws of hydraulics or capillary attraction; yet it is certainly assisted by these, and altogether approaches very near to a purely causal change. On the other hand, the movements of the Hedysarum gyrans and the Mimosa pudica, although still following upon mere stimuli, are yet very like movements which follow upon motives, and seem almost to wish to make the transition.