This existence of an unobserved real is integral to Bhaskar's ontology, which contends (in opposition to the various strains of positivism which have dominated both natural and social science in the twentieth century) that 'real structures exist independently of and are often out of phase with the actual patterns of events'. In social science, this has made his approach popular amongst contemporary Marxists — notably Alex Callinicos – who postulate the existence of real social forces and structures which might not always be observable.