All that we know of the external world of nature is only a certain relation of the forces of nature to inevitability, or of the essence of life to the laws of reason.
The great natural forces lie outside us and we are not conscious of them; we call those forces gravitation, inertia, electricity, animal force, and so on, but we are conscious of the force of life in man and we call that freedom.
But just as the force of gravitation, incomprehensible in itself but felt by every man, is understood by us only to the extent to which we know the laws of inevitability to which it is subject (from the first knowledge that all bodies have weight, up to Newton's law), so too the force of free will, incomprehensible in itself but of which everyone is conscious, is intelligible to us only in as far as we know the laws of inevitability to which it is subject (from the fact that every man dies, up to the knowledge of the most complex economic and historic laws).
All knowledge is merely a bringing of this essence of life under the laws of reason.
Man's free will differs from every other force in that man is directly conscious of it, but in the eyes of reason it in no way differs from any other force. The forces of gravitation, electricity, or chemical affinity are only distinguished from one another in that they are differently defined by reason. Just so the force of man's free will is distinguished by reason from the other forces of nature only by the definition reason gives it. Freedom, apart from necessity, that is, apart from the laws of reason that define it, differs in no way from gravitation, or heat, or the force that makes things grow; for reason, it is only a momentary undefinable sensation of life.
And as the undefinable essence of the force moving the heavenly bodies, the undefinable essence of the forces of heat and electricity, or of chemical affinity, or of the vital force, forms the content of astronomy, physics, chemistry, botany, zoology, and so on, just in the same way does the force of free will form the content of history. But just as the subject of every science is the manifestation of this unknown essence of life while that essence itself can only be the subject of metaphysics, even the manifestation of the force of free will in human beings in space, in time, and in dependence on cause forms the subject of history, while free will itself is the subject of metaphysics.
In the experimental sciences what we know we call the laws of inevitability, what is unknown to us we call vital force. Vital force is only an expression for the unknown remainder over and above what we know of the essence of life.
So also in history what is known to us we call laws of inevitability, what is unknown we call free will. Free will is for history only an expression for the unknown remainder of what we know about the laws of human life.