Chapter III, 5

Let us review the whole series of forms of causality once more. Causes in the narrowest sense, then stimuli, and finally motives—which divide in turn into perceptual and abstract motives—stand clearly apart. As we pass upward through the series of beings, we notice that cause and effect draw further apart, become more distinct and more unlike each other. The cause becomes less and less material and tangible; less and less seems to lie in the cause, and more and more in the effect. Taken together, these changes make the connection between cause and effect less immediately graspable and intelligible. Everything just described is least apparent in mechanical causality, which is therefore the easiest of all to grasp. This gave rise, in the previous century, to the mistaken endeavor, still surviving in France and recently appearing in Germany too, to reduce every other form of causality to mechanics: to explain all physical and chemical processes by mechanical causes, and then the process of life by those physical and chemical processes. A striking body moves a resting one, losing as much motion as it communicates. Here we seem to see the cause migrate into the effect: both are wholly of the same kind, precisely commensurable and tangible. This is really so with all purely mechanical effects. But as we ascend, we find less and less of this and more of the relationship described above. Consider, at each stage, the relation between heat as cause and its various effects—expansion, incandescence, melting, vaporization, combustion, thermoelectricity and so forth; or between evaporation as cause and cooling or crystallization as effects; or between the friction of glass as cause and free electricity, with its strange phenomena, as effect; or between the slow oxidation of the plates as cause and galvanism, with all its electrical, chemical and magnetic phenomena, as effect. Cause and effect become increasingly distinct and unlike; their connection becomes less intelligible. The effect seems to contain more than its cause could supply, as the cause appears less and less material and tangible. All this becomes clearer still when we turn to organic bodies. Mere stimuli are now the causes: some external, such as light, warmth, air, soil and food; others internal, arising from the action of fluids and parts upon one another. Their effect presents itself as life in its endless complexity and countless differences of kind, in the manifold forms of the plant and animal worlds∗).

∗) A fuller account of this divergence between cause and effect is given in “Willen in der Natur,” under “Astronomie,” S. 307 of the 6th volume of this edition.

But has the necessity established by the relation between cause and effect diminished as that relation has become increasingly heterogeneous, incommensurable and unintelligible? Not at all, not in the least. With the same necessity with which a rolling ball sets a resting one in motion, a Leyden jar must discharge when touched with the other hand; arsenic must kill every living thing; and a seed that, kept dry, showed no change for thousands of years must germinate, grow and develop into a plant as soon as it is placed in suitable soil and exposed to air, light, warmth and moisture. The cause is more complicated and the effect more unlike it, but the necessity with which the effect occurs is not diminished by a hair’s breadth.

In the life of a plant and the vegetative life of an animal, the stimulus differs greatly in every respect from the organic function it produces, and the two are clearly distinct. Yet they are not actually separated: some contact, however fine and invisible, must exist between them. Complete separation appears only in animal life, whose actions are produced by motives. Here the cause, previously still materially connected with its effect, stands wholly detached from it, of an entirely different nature: something initially immaterial, a mere representation. In the motive that produces an animal’s movement, the difference in kind between cause and effect, their separation, their incommensurability, the immateriality of the cause and hence its apparent insufficiency compared with the effect, have reached their highest degree. Their relation would become absolutely incomprehensible if we knew it only from outside, as we know the other causal relations. But here an entirely different kind of knowledge, an inward knowledge, supplements the outward one. We know intimately the process that occurs as effect once the cause has appeared, and give it a term of its own: will. Yet here too, just as with the stimulus above, we declare that the causal relation has lost none of its necessity as soon as we recognize it as causal and think it through this essential form of our understanding. We also find motivation wholly analogous to the other two forms of the causal relation already discussed: it is merely the highest stage to which they rise by a very gradual transition. On the lowest levels of animal life, the motive is still closely related to the stimulus. Zoophytes, radiates in general, and the Acephala among mollusks possess only a faint twilight of consciousness: just enough to perceive their food or prey and seize it when it offers itself, and, if need be, exchange their location for a more favorable one. On these low levels, therefore, the action of a motive lies before us as clearly, immediately, decisively and unambiguously as that of a stimulus. Small insects are drawn by the glow of light into the flame itself; flies settle trustingly on the head of a lizard that has just swallowed others of their kind before their eyes. Who would dream of freedom here? In the higher, more intelligent animals, the action of motives becomes increasingly indirect: a motive stands more clearly apart from the action it produces. We might even use this varying distance between motive and action as a measure of an animal’s intelligence. In humans, that distance becomes immeasurable. Even in the cleverest animals, however, the representation that becomes the motive of their action must still be perceptual. Even where a choice is possible, it can only be between things present in perception. A dog hesitates between its master’s call and the sight of a female dog: the stronger motive will determine its movement, which then occurs as necessarily as a mechanical effect. In mechanics too, we see a body displaced from equilibrium sway for a while first to one side and then to the other, until the side on which its center of gravity lies is decided and it falls that way. As long as motivation is limited to perceptual representations, its kinship with stimulus and cause in general is also made evident by this: the motive, as an effective cause, must be something real and present, and must still act physically on the senses through light, sound or smell, however indirectly. Moreover, the cause lies as openly before the observer as the effect. He sees the motive appear and the animal’s action inevitably follow, unless another equally evident motive, or training, counteracts it. It is impossible to doubt the connection between the two. Accordingly, no one will think of attributing freedom of indifferent choice to animals—that is, action determined by no cause.

Let us look once more at the whole range of forms of causality. Within it we can clearly distinguish causes in the narrowest sense of the word, then stimuli, and finally motives, which in turn divide into perceptual and abstract motives. As we move from lower to higher beings in this respect, we notice that cause and effect move further apart, become more clearly distinct, and differ more in kind. The cause becomes less and less material and tangible. As a result, less and less seems to be contained in the cause, and more and more in the effect. Taken together, all this makes the connection between cause and effect harder to grasp and understand directly. Everything just mentioned applies least to mechanical causality, which is therefore the easiest kind to understand. This gave rise, in the last century, to the mistaken attempt to reduce every other kind of causality to mechanical causality, explaining all physical and chemical processes through mechanical causes, and then explaining the process of life through those physical and chemical processes. This effort continues in France and has recently appeared in Germany too. One body strikes another that is at rest and moves it. The first loses as much motion as it gives the second. Here we seem to see the cause pass over into the effect. Both are entirely of the same kind, exactly measurable against each other, and tangible. This is really true of all purely mechanical effects. But we will find that it becomes less and less true, and that what was said above takes its place, the higher we go, if we consider the relation between cause and effect at each level. Examples are the relation between heat as a cause and its various effects, such as expansion, glowing, melting, vaporization, combustion, thermoelectricity, and so on; between evaporation as a cause and cooling or crystallization as effects; between rubbing glass as a cause and free electricity, with its strange phenomena, as an effect; or between the slow oxidation of plates as a cause and galvanism, with all its electrical, chemical, and magnetic phenomena, as an effect. So cause and effect become more and more distinct and different in kind, and their connection becomes harder to understand. The effect seems to contain more than the cause could supply, as the cause proves less and less material and tangible. All this becomes still clearer when we turn to organic bodies. Here the causes are mere stimuli. Some are external, such as those of light, heat, air, soil, and food; some are internal, as fluids and parts act on one another. Their effect is life, with its infinite complexity and countless differences of kind, appearing in the varied forms of the plant and animal worlds. ∗)

∗) A more detailed account of this growing separation of cause and effect can be found in “Willen in der Natur,” under “Astronomie,” p. 307 of volume 6 of this edition.

But as the relation between cause and effect becomes increasingly different in kind, impossible to measure on a common scale, and hard to understand, has the necessity it establishes also decreased? Not at all, not in the slightest. Just as necessarily as a rolling ball sets a stationary one in motion, a Leyden jar must discharge when touched with the other hand; arsenic must kill every living thing; and a seed that has shown no change for thousands of years while stored dry must germinate, grow, and develop into a plant as soon as it is put in suitable soil and exposed to air, light, warmth, and moisture. The cause is more complex and the effect is more different in kind, but the necessity with which it occurs is not a hair less.

In plant life and in an animal's vegetative life, the stimulus is indeed very different in every respect from the organic function it produces, and the two are clearly distinct. Yet they are not actually separate. There must be some contact between them, however subtle and invisible. Complete separation occurs only in animal life, whose actions are brought about by motives. Here the cause, which until now still had a material connection with the effect, stands entirely detached from it. It is of a completely different nature: something initially immaterial, a mere representation. So in the motive that makes an animal move, the difference in kind between cause and effect, their separation, the impossibility of measuring them on a common scale, and the immaterial nature of the cause—and thus its apparent lack of sufficient content to account for the effect—have reached their highest point. The relation between them would become absolutely incomprehensible if, like the other causal relations, we knew it only from outside. But here knowledge of a completely different kind, inner knowledge, supplements our knowledge from outside. We are intimately familiar with the process that takes place here as the effect once the cause has appeared. We give it a special term: will. Yet here too, just as with the stimulus discussed above, the causal relation has lost none of its necessity. We say as much as soon as we recognize it as a causal relation and think of it through this form essential to our understanding. We also find motivation completely analogous to the other two forms of the causal relation discussed above. It is simply the highest level to which they rise in an entirely gradual transition. At the lowest levels of animal life, the motive is still closely related to the stimulus. Zoophytes, radiates in general, and the headless mollusks have only a faint glimmer of consciousness. They have just enough to perceive their food or prey and seize it when it presents itself, and perhaps to move to a more favorable spot. At these low levels, then, the effect of a motive is still as clear, direct, definite, and unmistakable to us as the effect of a stimulus. Small insects are drawn by the glow of a light right into its flame. Flies trustingly land on the head of a lizard that has just swallowed others of their kind before their eyes. Who would dream of freedom here? In the higher, more intelligent animals, motives act less and less directly. The motive becomes more clearly separated from the action it produces. We could even use these differences in the distance between motive and action as a measure of animals' intelligence. In human beings this distance becomes immeasurable. But even in the cleverest animals, the representation that becomes the motive for what they do must still be perceptual. Even where a choice becomes possible, it can only be between things currently presented to their senses. A dog stands hesitating between its master's call and the sight of a female dog. The stronger motive will determine its movement. But then the movement follows as necessarily as a mechanical effect. Even in a mechanical case, we see a body thrown off balance rock first to one side and then to the other for a time, until it becomes clear which side its center of gravity is on, and it falls that way. As long as motivation is limited to perceptual representations, its relationship to the stimulus and to causes in general is also obvious in another respect. The motive, as the effective cause, must be something real and present. Through light, sound, or smell, it must still act physically on the senses, even if very indirectly. Moreover, the cause is as open to the observer here as the effect. The observer sees the motive appear and the animal's action inevitably follow, unless another equally obvious motive, or training, works against it. It is impossible to doubt the connection between the two. So no one would think of attributing to animals a freedom of choice indifferent to its alternatives—that is, action not determined by any cause.