I believe—as I shall try to prove in a later lecture—that desire, like force in mechanics, is of the nature of a convenient fiction for describing shortly certain laws of behaviour. A hungry animal is restless until it finds food; then it becomes quiescent.

我相信——正如我将在后面的演讲中试图证明的那样——欲望就像力学中的力一样，具有一种方便的虚构的性质，可以快速描述某些行为规律。饥饿的动物在找到食物之前会焦躁不安；然后它变得静止。