materialist, and together with J. J. C. Smart (1920–2012) the leading Australian philosopher of the second half of the twentieth century. Armstrong defended an uncompromising scientific materialism, together with a functionalist theory of mind. However, he saw scientific laws as describing necessitation relations between universals, about which he was a realist, but of an Aristotelian rather than a Platonist persuasion. He defended the view that every true proposition requires something to make it true, a ‘truthmaker’ and therefore holds an ontology of states of affairs, reminiscent of Wittgenstein’s Tractatus, especially in that it is the combinatorial properties of states of affairs that underlies the theory of necessity and possibility. Books include Perception and the Physical World (1961), A Materialist Theory of the Mind (1968), Belief, Truth and Knowledge (1973), What is a Law of Nature? (1983), A World of States of Affairs (1997), The Mind-Body Problem: An Opinionated Introduction (1999), Truth and Truthmakers (2004), Sketch for a Systematic Metaphysics (2010).