The crucial issue for realist naturalism is the sense to be given to structural concepts in the social sciences. Unlike reductionist forms of positivist naturalism, which tend to be attracted by behaviourism, a realist naturalism emphasises the stratification of reality as a general metaphysical principle. In the form defended here, it also accepts the "hermeneutic" principle that the concepts and theories of the social sciences must make substantial reference to those of actors in the life-world. At the centre of our social ontology there must be, then, the commonsense picture of physically distinct persons capable of independent action: what Harré and Secord ironically called "the anthropomorphic model of man".¹