But let us descend to created things, which are all determined by external causes to exist and to produce their effects in a definite and determinate way. To understand this clearly, consider a simple example. A stone receives, from an external cause that starts it moving, a certain quantity of motion; and by this it then necessarily continues to move, although the impulse of the external cause has ceased.

Therefore, the stone’s continuing to move is compelled, not because it is necessary but because it must be defined [here = ‘made definite’, ‘given its properties’] by the impulse of the external cause. What I say here about the stone applies to any individual thing whatever, however complex in structure and operations; every individual thing is necessarily determined by some external cause to exist and produce effects in a certain and determinate way.

Now suppose that the stone is thinking while it moves, and that it knows that it’s doing its best to continue to move. Being conscious only of its effort and not being at all indifferent, the stone will believe that it is very free and perseveres in motion purely because it wills to. This is the famous human freedom everyone brags of having, which consists only in this: that men are conscious of their appetite and ignorant of the causes by which they are determined. So the infant believes that he freely wants the milk; the angry boy that he wants vengeance; and the timid, flight. The drunk believes that it’s from a free decision of his mind that he says things that next morning he soberly wishes he hadn’t said. Similarly, the madman, the chatterbox, and a many people of this kind believe that they act from a free decision of the mind, and not that they are carried away by impulse.

Because this prejudice is innate in all men, they aren’t easily freed of it. Experience teaches abundantly that nothing is less in man’s power than to restrain his appetites, and that when men are torn by contrary affects they often ‘see the better and follow the worse’ [Ovid]; yet they still believe themselves to be free because when they want something only slightly their appetite for it can easily be restrained by the memory of something else that comes to mind more easily, and they mistake this restraint as an exercise of their free will.