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. The contraction of the pupils of the eyes as the light is increased is due to stimuli, but it passes into movement which is due to motive; for it takes place, because too strong lights would affect the retina painfully, and to avoid this we contract the pupils. The occasion of an erection is a motive, because it is an idea, yet it operates with the necessity of a stimulus, i.e., it cannot be resisted, but we must put the idea away in order to make it cease to affect us. This is also the case with disgusting things, which excite the desire to vomit. Thus we have treated the instinct of animals as an actual link, of quite a distinct kind, between movement following upon stimuli, and action following upon a known motive. Now we might be asked to regard breathing as another link of this kind. It has been disputed whether it belongs to the voluntary or the involuntary movements, that is to say, whether it follows upon motive or stimulus, and perhaps it may be explained as something which is between the two. Marshall Hall (“On the Diseases of the Nervous System,” § 293 sq.) explains it as a mixed function, for it is partly under the influence of the cerebral (voluntary), and partly under that of the spinal (non-voluntary) nerves. However, we are finally obliged to number it with the expressions of will which result from motives. For other motives, i.e., mere ideas, can determine the will to check it or accelerate it, and, as is the case with every other voluntary action, it seems to us that we could give up breathing altogether and voluntarily suffocate. And in fact we could do so if any other motive influenced the will sufficiently strongly to overcome the pressing desire for air. According to some accounts Diogenes actually put an end to his life in this way (Diog. Laert. VI. 76). Certain negroes also are said to have done this (F. B. Osiander “On Suicide” [1813] pp. 170–180). If this be true, it affords us a good example of the influence of abstract motives, i.e., of the victory of distinctively rational over merely animal will. For, that breathing is at least partially conditioned by cerebral activity is shown by the fact that the primary cause of death from prussic acid is that it paralyses the brain, and so, indirectly, restricts the breathing; but if the breathing be artificially maintained till the stupefaction of the brain has passed away, death will not ensue. We may also observe in passing that breathing affords us the most obvious example of the fact that motives act with just as much necessity as stimuli, or as causes in the narrowest sense of the word, and their operation can only be neutralised by antagonistic motives, as action is neutralised by re-action. For, in the case of breathing, the illusion that we can stop when we like is much weaker than in the case of other movements which follow upon motives; because in breathing the motive is very powerful, very near to us, and its satisfaction is very easy, for the muscles which accomplish it are never tired, nothing, as a rule, obstructs it, and the whole process is supported by the most inveterate habit of the individual. And yet all motives act with the same necessity. The knowledge that necessity is common to movements following upon motives, and those following upon stimuli, makes it easier for us to understand that that also which takes place in our bodily organism in accordance with stimuli and in obedience to law, is yet, according to its inner nature—will, which in all its manifestations, though never in itself, is subordinated to the principle of sufficient reason, that is, to necessity.32 Accordingly, we shall not rest contented with recognising that animals, both in their actions and also in their whole existence, bodily structure and organisation, are manifestations of will; but we shall extend to plants also this immediate knowledge of the essential nature of things which is given to us alone. Now all the movements of plants follow upon stimuli; for the absence of knowledge, and the movement following upon motives which is conditioned by knowledge, constitutes the only essential difference between animals and plants. Therefore, what appears for the idea as plant life, as mere vegetation, as blindly impelling force, we shall claim, according to its inner nature, for will, and recognise it as just that which constitutes the basis of our own phenomenal being, as it expresses itself in our actions, and also in the whole existence of our body itself.
It only remains for us to take the final step, the extension of our way of looking at things to all those forces which act in nature in accordance with universal, unchangeable laws, in conformity with which the movements of all those bodies take place, which are wholly without organs, and have therefore no susceptibility for stimuli, and have no knowledge, which is the necessary condition of motives. Thus we must also apply the key to the understanding of the inner nature of things, which the immediate knowledge of our own existence alone can give us, to those phenomena of the unorganised world which are most remote from us. And if we consider them attentively, if we observe the strong and unceasing impulse with which the waters hurry to the ocean, the persistency with which the magnet turns ever to the north pole, the readiness with which iron flies to the magnet, the eagerness with which the electric poles seek to be re-united, and which, just like human
