Lon Fuller rejected legal positivism because he believed that the ‘procedural morality of law’ established a necessary connection between law and morals. Underpinning
his argument is a claim that law is a purposive activity grounded by a relationship of political reciprocity between lawgivers and legal subjects. This paper argues that his reliance on political reciprocity implicates a necessary connection between his procedural morality and
an unarticulated ‘substantive morality of law’: it presupposes that law is properly understood
by reference to the political task of achieving a common good. To establish this necessary connection, I propose we look to Alasdair MacIntyre. Understanding law as a ‘social
practice’, on MacIntyre’s terms, can provide the necessary socio-political context to explain why and how legal practice is conditioned by political reciprocity. If we apply MacIntyre’s distinction between the internal and external goods of a social practice, legal positivism can
be understood as confusing law as a co-operative social practice with the instrumentalisation of that practice by legal officials
