 A positivist account of the existence and content of law, along any of the above lines, offers a theory of the validity of law in one of the two main senses of that term (see Harris 1979: 107–111). Kelsen says that validity is the specific mode of existence of a norm. In this sense a valid law is one that is systemically valid in the jurisdiction—it is part of the legal system, and identified as such by virtue of its dependence on the system’s social sources. The idea is distinct from that of validity as moral propriety, i.e., a sound justification for respecting the norm. For the legal positivist, this depends on the norm’s merits. One indication that these senses differ is that one may know that a society has a legal system, and know what its laws are, without having any idea whether they are morally justified. For example, one may know that the law of ancient Athens included the punishment of ostracism without knowing whether it was justified, because one does not know enough about its effects, about the social context, and so forth.