§68

We could draw a boundary to the concepts 'number' or 'game'. BUT as it stands they do not have clear boundaries and this doesn't worry us.

We might want to draw a boundary for some purpose (e.g. if there was a 'great-tournament of games' then we might want to draw a limit to which activities will be admitted to the great tournament and which won't).

You might think it a problem that our concept 'game' does not have clear boundaries as it is ordinarily used - that there are not rules which determine exactly what is to count as a game in every instance. But we don't worry about the fact that many activities are not completely bounded by rules e.g. there are aspects of the game of tennis which are not bounded by rules - there is no rule that says you can't throw a ball above a certain height when serving.