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for then indeed we fall into an irremovable error. Then, as I have already said, we maintain the view, that motion has two radically different primary principles with a solid partition-wall between them: i.e. movement by means of causes, and movement by means of the will. The first of these must then remain for ever incomprehensible as to its innermost essence, because, after all its explanations, there is still left that unknown x which contains the more, the higher the object under consideration stands in the scale of beings; while the second, movement by the will, presents itself as entirely disconnected from the principle of causality; as without reason; as freedom in individual actions: in other words, as completely opposed to Nature and utterly unexplainable. On the other hand, if the above-mentioned union of our external and internal knowledge has once been accomplished at the point where both meet, we then recognise two identities in spite of all accidental differences. That is to say, we recognise the identity of causality with itself on every degree of the scale of beings, and the identity of the x, which at first was unknown (i.e. of physical forces and vital phenomena), with the will which is within us. We recognise, I say, firstly the essential identity of causality under the various forms it is forced to assume on the different degrees of the scale, as it may manifest itself, now as a mechanical, chemical, or physical cause, now as a stimulus, and again as a perceptible or an abstract motive: we know it to be one and the same, not only when a propelling body loses as much movement as it imparts by impact, but also when in the combats of thought against thought, the victorious one, as the more powerful motive, sets Man in motion, a motion which follows with no less necessity than that of the ball which is struck. Where we ourselves are the things set in motion, where therefore the kernel of the process is well and intimately known to us,
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