It is often said that the nature of Force itself is unknown and only its manifestation apprehended. But, in the first place, it may be replied, every article in the import of Force is the same as what is specified in the Exertion: and the explanation of a phenomenon by a Force is to that extent a mere tautology. What is supposed to remain unknown, therefore, is really nothing but the empty form of reflection-into-self, by which alone the Force is distinguished from the Exertion,--and that form too is something familiar. It is a form that does not make the slightest addition to the content and to the law, which have to be discovered from the phenomenon alone. Another assurance always given is that to speak of forces implies no theory as to their nature: and that being so, it is impossible to see why the form of Force has been introduced into the sciences at all. In the second place the nature of Force is undoubtedly unknown: we are still without any necessity binding and connecting its content together in itself, as we are without necessity in the content, in so far as it is expressly limited and hence has its character by means of another thing outside it. (1) Compared with the immediate relation of whole and parts, the relation between force and its putting-forth may be considered infinite. In it that identity of the two sides is realised, which in the former relation only existed for the observer. The whole, though we can see that it consists of parts, ceases to be a whole when it is divided: whereas force is only shown to be force when it exerts itself, and in its exercise only comes back to itself. The exercise is only force once more. Yet, on further examination even this relation will appear finite, and finite in virtue of this mediation: just as, conversely, the relation of whole and parts is obviously finite in virtue of its immediacy. The first and simplest evidence for the finitude of the mediated relation of force and its exercise is, that each and every force is conditioned and requires something else than itself for its subsistence. For instance, a special vehicle of magnetic force, as is well known, is iron, the other properties of which, such as its colour, specific weight, or relation to acids, are independent of this connexion with magnetism. The same thing is seen in all other forces, which from one end to the other are found to be conditioned and mediated by something else than themselves. Another proof of the finite nature of force is that it requires solicitation before it can put itself forth. That through which the force is solicited, is itself another exertion of force, which cannot put itself forth without similar solicitation. This brings us either to a repetition of the infinite progression, or to a reciprocity of soliciting and being solicited. In either case we have no absolute beginning of motion. Force is not as yet, like the final cause, inherently self-determining: