 The most influential theory to have denied the communication model is that of Ronald Dworkin, as it emerged in his argument against the idea that the law of a country is a system of rules. H.L.A.Hart had tried to explain the nature of a legal system on the basis of social rules for identifying the law of a community, which provide shared tests of validity for rules of the system. Hart treated it as obvious that such rules commonly identify the acts of law-making authorities as sources of law, conferring power on those authorities to make law, and that (subject to qualifications that are part of the communication model such as those listed above) the law becomes what a lawmaker conveys that it is to be, in the communicative act by which it exercises such a power.