This short sketch of the three forms of causality will suffice here. They are more fully described in my Prize-essay on Free Will.[67] One thing, however, still remains to be urged. The difference between cause, stimulus, and motive, is obviously only a consequence of the various degrees of _receptivity_ of beings; the greater their receptivity, the feebler may be the nature of the influence: a stone needs an impact, while man obeys a look. Nevertheless, both are moved by a sufficient cause, therefore with the same necessity. For '_motivation_'[68] is only causality passing through knowledge; the intellect is the medium of the motives, because it is the highest degree of receptivity. By this, however, the law of causality loses nothing whatever of its rigour and certainty; for motives are causes and operate with the same necessity which all causes bring with them. This necessity is easy to perceive in animals because of the greater simplicity of their intellect, which is limited to the perception of what is present. Man's intellect is double: for not only has he intuitive, but abstract, knowledge, which last is not limited to what is present. Man possesses Reason; he therefore has a power of elective decision with clear consciousness: that is, he is able to weigh against one another motives which exclude each other, as such; in other terms, he can let them try their strength on his will. The most powerful motive then decides him, and his actions ensue with just the same necessity as the rolling of a ball after it has been struck. Freedom of Will[69] means (not professorial twaddle but) "_that a given human being, in a given situation, can act in two different ways_." But the utter absurdity of this assertion is a truth as certain and as clearly proved, as any truth can be which passes the limits of pure mathematics. In my Essay on Free Will, to which the Norwegian Society awarded the prize, this truth is demonstrated more clearly, methodically, and thoroughly than has been done before by anyone else, and this moreover with special reference to those facts of our consciousness by which ignorant people imagine that absurdity to be confirmed. In all that is essential however, Hobbes, Spinoza, Priestley, Voltaire, and even Kant[70] already taught the same doctrine. Our professional philosophers, of course, do not let this interfere with their holding forth on Free Will, as if it were an understood thing which had never been questioned. But what do these gentlemen imagine the above-named great men to have come into the world for, by the grace of Nature? To enable them (the professors) to earn their livelihood by philosophy?--Since I had proved this truth in my prize-essay more clearly than had ever been done before, and since moreover a Royal Society had sanctioned that proof by placing my essay among its memoranda, it surely behoved these worthies, considering the views they held, to make a vigorous attack upon so