We cannot ascertain causes by mere introspective reasoning, we cannot derive them out of our head. Matter, materials, sense perceptions are required for this purpose. A definite cause requires a definite material, a definite amount of sense perceptions. In the abstract unity of nature, the variations of matter are represented by the variations of concrete quantities. Every quantity is given in time before and after a certain other quantity, as antecedent and subsequent. The general element of the antecedent is called cause, the general element of the subsequent, effect.
When the wind sways a forest, the yielding character of the forest is as much instrumental in producing this effect as the bending power of the wind. The cause of a thing is its connection with other things. The fact that the same wind leaves rocks and walls standing shows that the cause is not qualitatively different from the effect, but that it is a matter of aggregate effects. If nevertheless science or knowledge determines any special fact to be the cause of any change, that is to say of any succession of phenomena, this cause is no longer regarded as the external creator, but merely as the general mode, the immanent method of succession. A definite cause can be ascertained only when we have under consideration a definite circle, series, or number of changes, the cause of which is to be determined. And within a definite circle of succeeding phenomena, that which generally precedes is their cause.
The wind which sways a forest differs from wind as a general cause only in that the latter has other general effects, inasmuch as it howls in one place, stirs up dust in another, or acts in many different ways. In the special case of the forest, the wind is a cause only in so far as it precedes the swaying of the trees. But in the case of rocks and walls, the solidity precedes the wind and is therefore the general cause of their resistance to the swaying power of the wind. In a still wider circle of hurricane phenomena, a gentle wind may be regarded as a cause of the stability of the objects last mentioned.
The quantity or number of given objects varies the name of their cause. If a certain company of people return from a walk in a tired condition, this change of condition is just as much due to the physical weakness of the people as to the walk. In other words, a manifestation has in itself no cause which can be separated from it. Everything which was connected with a phenomenon has contributed toward its appearance. In the case of the promenaders, the physical constitution of their bodies has to be considered as well as the physical constitution and length of the road and duration of the walk. If reason is nevertheless called upon to determine the special cause of some concrete change, for instance, of a tired feeling, it is simply a question of determining which one of the various factors has contributed most to that feeling. In this case as well as in all others, the work of reason consists in developing the general from the concrete, that is to say in this case, singling out from a given number of tired sensations that which generally precedes the tired feeling. If most of the promenaders or all of them are found to be tired, the walk will be considered as the cause. But if only a few are tired, the weak constitution of these people will be considered as the general cause of their tired condition.
To use another illustration: If the discharge of a shot frightens some birds, this effect is due to the combined action of the shot and the timidity of the birds. If the majority of the birds fly away, the shot will be considered as the cause. But if the minority fly away, their timidity will be regarded as the cause.
Effects are subsequences. Since all things in nature follow other things and all things have an antecedent and a subsequent, we may call the natural, the real, the sense perceptions absolute effects, having no cause unless we find one with our faculty of thought by systematizing the given material. Causes are mental generalizations of perceptible changes. The supposed relation of cause and effect is a miracle, a creation of something out of nothing. For this reason this relation has been and still is an object of speculative reasoning. The speculative cause creates its effects. But in reality the effects are the material out of which the brain, or science, forms its causes. The cause concept is a product of reason; not of "pure" reason, but of reason married to the world of sense perceptions.
If Kant maintains that the statement: "Every change has its cause" is an a priori truth which we cannot experience because no one can possibly experience all changes, although every one has the irrefutable feeling of the correctness of this statement, we know now that this statement expresses merely the experience that the phenomenon which we call reason recognizes the uniform element in all multiformity. Or in other words, we now know that the development of the general element out of the concrete facts is called reason, thought, or mind. The secure knowledge that every change has its cause is nothing else but the conviction that we are thinking human beings. Cogito, ergo sum. I think, therefore I am. We have experienced the nature of our reason instinctively even if we have not analyzed it scientifically. We are as well aware of the faculty of our reason to abstract a cause out of every given change, as we are that every circle is round, that a is equal to a. We know that the general is the product of reason, and reason produces this general thing in contact with every given object. And since all objects before and after a certain other object are temporal changes, it follows that all changes which we as thinking beings experience must have a general antecedent, a cause.
Already the English sceptic Hume felt that true causes are different from assumed causes. According to him the concept of a cause contains nothing but the experience of that which generally precedes a certain phenomenon. Kant rightfully remarks on the other hand that the conception of cause and effect expresses a far more intimate relation than that indicated by a loose and accidental succession, and that the concept of a cause rather comprises that of a certain effect as a necessity and strict general result. Therefore he claimed that there must be something a priori in reason which cannot be experienced and which extends beyond experience.
We reply to the materialists who deny all autonomy of the mind and hope to detect causes by experience alone that the general necessity which presupposes the relation of cause and effect represents an impossible experience. And we reply to the idealists: Although reason explores causes which cannot be experienced, this research cannot take place a priori, but only a posteriori, only on the basis of empirically given effects. It is true that the mind alone discovers the imperceptible and abstract generality, but it does so only within the circle of certain given sense perceptions.