Supposing I teach someone the use of the word “yellow” by repeatedly pointing to a yellow patch and pronouncing the word. On another occasion I make him apply what he has learnt by giving him the order, “choose a yellow ball out of this bag”. What was it that happened when he obeyed my order? I say: “possibly just this: he heard my words and took a yellow ball from the bag.” Now you may be inclined to think that this couldn't possibly have been all; and the kind of thing that you would suggest is that he imagined something yellow when he understood the order, and then chose a ball according to his image. To see that this is not necessary remember that I could have given him the order, “Imagine a yellow patch”. Would you still be inclined to assume that he first imagines a yellow patch, just understanding my order, and then imagines a yellow patch to match the first? (Now I don't say that this is not possible. Only, putting it in this way immediately shows you that it need not happen. This, by the way, illustrates the method of philosophy.)