(Sektion 205: Philosophische Untersuchungen von Ludwig Wittgenstein).

205. "It is just noteworthy about intention, as a mental process, that the existence of a custom, of a technique, is not necessary for it. It is thinkable, for example, for two people two play chess in a world in which otherwise no games existed; and even only to begin a chess game,--and then be interrupted."

But is the chess game not defined through the rules? And how are these rules present in the mind of the person who intends to play chess?