Ranging over a remarkable number of topics, from behaviourism, the will and knowledge to perception, bodily sensation and introspection, Armstrong argues that mental states play a causally intermediate role between stimuli, other mental states and behavioural responses. He uses several illuminating examples to illustrate this, such as the classic case of pain.

This Routledge Classics edition includes a new Foreword by Peter Anstey, placing Armstrong's book in helpful philosophical and historical context.