Critical realism is a philosophical approach to understanding science, and in particular social science, initially developed by Roy Bhaskar (1944–2014). It specifically opposes forms of empiricism and positivism by viewing science as concerned with identifying causal mechanisms. In the last decades of the twentieth century it also stood against various forms of postmodernism and poststructuralism by insisting on the reality of objective existence. In contrast to positivism's methodological foundation, and poststructuralism's epistemological foundation, critical realism insists that (social) science should be built from an explicit ontology. Critical realism is one of a range of types of philosophical realism, as well as forms of realism advocated within social science such as analytic realism and subtle realism.