David Malet Armstrong (8 July 1926 – 13 May 2014), often D. M. Armstrong, was an Australian philosopher. He is well known for his work on metaphysics and the philosophy of mind, and for his defence of a factualist ontology, a functionalist theory of the mind, an externalist epistemology, and a necessitarian conception of the laws of nature. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 2008.
Keith Campbell said that Armstrong’s contributions to metaphysics and epistemology “helped to shape philosophy’s agenda and terms of debate”, and that Armstrong’s work “always concerned to elaborate and defend a philosophy which is ontically economical, synoptic, and compatibly continuous with established results in the natural sciences”
Armstrong’s philosophy is broadly naturalistic. In Sketch for a Systematic Metaphysics, Armstrong states that his philosophical system rests upon “the assumption that all that exists is the space time world, the physical world as we say”. He justifies this by saying that the physical world “seems obviously to exist” while other things “seem much more hypothetical”. From this fundamental assumption flows a rejection of abstract objects including Platonic forms.
Armstrong holds to a physicalist, functionalist theory of the mind. He initially was attracted to Gilbert Ryle’s The Concept of Mind and the rejection of Cartesian dualism. Armstrong did not accept behaviourism and instead defended a theory he referred to as the “central-state theory” which identifies mental states with the state of the central nervous system. In A Materialist Theory of Mind, he accepted that mental states such as consciousness exist, but stated that they can be explained as physical phenomena. Armstrong attributes his adoption of the central-state theory to the work of J. J. C. Smart—specifically the paper ‘Sensations and Brain Processes’—and traces the lineage from there to Ullin Place’s 1956 paper ‘Is Consciousness a Brain Process?’
Stephen Mumford said that Armstrong’s A Materialist Theory of Mind “represents an authoritative statement of Australian materialism and was, and still is, a seminal piece of philosophy”.