The main purpose of this article is to question the soundness of a recent attack on legal positivism launched by Professor Ronald M. Dworkin in his essay “Is law a system of rules?”1 I do not think any preliminary explanation of the strategy of my argument is necessary except for my use of a model taken from the rules of a game. I am aware of the important differences existing between legal norms and rules of games. But in spite of these differences law, as a normative structure, shares some problematic features with other normative structures, those of games included, and the following non-legal model does, I think, throw light on some of the main issues discussed later.