David Malet Armstrong (b. 8 July 1926, Melbourne) is an Australian philosopher focused on epistemology, ontology and philosophy of mind. He is best known for his Materialist Theory of Mind, part of his materialist-physicalist project. Regarding properties, he defends an immanent realist conception of universals as the best way of understanding the interaction of particulars with laws of nature (in Universals: An Opinionated Introduction and the two-volume Universals and Scientific Realism). This fits into a more general project of defending the Wittgenstein-inspired notion of the world as a totality of states of affairs (in A World of States of Affairs). In epistemology, Armstrong is best known for his advocacy of an externalist theory of justification that requires a causal link between beliefs and the states of affairs that cause them (see Belief, Truth and Knowledge). Armstrong's philosophy hinges on a strongly affirmative view of science.
Armstrong was a student of Professor John Anderson at the University of Sydney and has stated that he is not tremendously interested in questions in the philosophy of language. Although interested in questions of ethics and political philosophy, Armstrong has not written about this area in any depth. He has stated that he is a supporter of liberal democracy, but with a conservative edge, and has been inspired by the work of Michael Oakeshott.
Armstrong's epistemology is reliabilist - that is, Armstrong identifies knowledge as true belief with a reliable, law-like (nomic) relationship between knower and world.
- Armstrong declares his unofficial motto as being "Put semantics last", see Interview with David Armstrong from Matters of the Mind: Poems, Essays and Interviews in Honour of Leonie Kramer.