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.