Take a position close to a smooth wall, so that one arm and hand, which are left hanging down alongside the body, are pressed over their entire length between body and wall. Try now to move the arm upward, pressing it against the wall as if you wanted to shift the latter. Apply all possible effort to this attempt, and maintain the effort for about one minute. Then step away quickly from the wall by more than the length of the arm, while keeping the arm hanging down by the side of the body in a state of complete relaxation. Provided all conditions are properly fulfilled, the arm will be found rising by itself in accordance with the aim of the earlier effort, until it reaches the horizontal. If the arm is then lowered again and left to itself, it will at once rise again, though not quite so high as before. This can be repeated several times until the last vestige of the automatic movement has faded away. Having thus ascertained by direct experience that there is a state of matter in which inertia is, to say the least, greatly diminished, we find ourselves in need of giving this state (which is present throughout nature wherever material changes are brought into existence magically) a name of its own, as we did with the two types of causation. A word suggests itself which, apart from expressing adequately the peculiar self-mobility which we have just brought to our experience, goes well alongside the word 'inert' by forming a kind of rhyme with it. This is the term 'alert'. With its help we shall henceforth distinguish between matter in the inert and alert conditions. We shall call the latter state 'alertness', and in order to have on the other side a word as similar as possible in outer form to alertness, we suggest replacing the usual term inertia by 'inertness'. Thus we shall speak of matter as showing the attribute of 'inertness', when it is subject to mechanical causation, of 'alertness', when it is subject to magical causation. Anyone who watches attentively the sensation produced by the rising arm in the above experiment will be duly impressed by the experience of the alertness prevailing in the arm as a result of the will's magical intervention. *