I can make this comparison because my body is the only object of which I know not merely the _one_ side, that of the idea, but also the other side which is called will. Thus, instead of believing that I would better understand my own organisation, and then my own knowing and willing, and my movements following upon motives, if I could only refer them to movements due to electrical, chemical, and mechanical causes, I must, seeing that I seek philosophy and not etiology, learn to understand from my own movements following upon motives the inner nature of the simplest and commonest movements of an unorganised body which I see following upon causes. I must recognise the inscrutable forces which manifest themselves in all natural bodies as identical in kind with that which in me is the will, and as differing from it only in degree. That is to say, the fourth class of ideas given in the Essay on the Principle of Sufficient Reason must be the key to the knowledge of the inner nature of the first class, and by means of the law of motivation I must come to understand the inner meaning of the law of causation. Spinoza (Epist. 62) says that if a stone which has been projected through the air had consciousness, it would believe that it was moving of its own will. I add to this only that the stone would be right. The impulse given it is for the stone what the motive is for me, and what in the case of the stone appears as cohesion, gravitation, rigidity, is in its inner nature the same as that which I recognise in myself as will, and what the stone also, if knowledge were given to it, would recognise as will. In the passage referred to, Spinoza had in view the necessity with which the stone flies, and he rightly desires to transfer this necessity to that of the particular act of will of a person. I, on the other hand, consider the inner being, which alone imparts meaning and validity to all real necessity (_i.e._, effect following upon a cause) as its presupposition. In the case of men this is called character; in the case of a stone it is called quality, but it is the same in both. When it is immediately known it is called will. In the stone it has the weakest, and in man the strongest degree of visibility, of objectivity. St. Augustine recognises, with a true instinct, this identity of the tendencies of all things with our own willing, and I cannot refrain from quoting his naïve account of the matter:—“_Si pecora essemus, carnalem vitam et quod secundum sensum ejusdem est amaremus, idque esset sufficiens bonum nostrum, et secundum hoc si esset nobis bene, nihil aliud quæreremus. Item, si arbores essemus, nihil quidem sentientes motu amare possemus: verumtamen id quasi appetere videremur, quo feracius essemus, uberiusque fructuosæ. Si essemus lapides, aut fluctus, aut ventus, aut flamma, vel quid ejusmodi, sine ullo quidem sensu atque vita, non tamen nobis deesset quasi quidam nostrorum locorum atque ordinis appetitus.