  The causal approach was also characteristic of D.M. Armstrong's careful conceptual analysis of mental states and processes, such as perception and the secondary qualities, sensation, consciousness, belief, desire, emotion, voluntary action, in his A Materialist Theory of the Mind (1968a) with a second edition (1993) containing a valuable new preface. Parts I and II of this book are concerned with conceptual analysis, paving the way for a contingent identification of mental states and processes with material ones. As had Brian Medlin, in an impressive critique of Ryle and defence of materialism (Medlin 1967), Armstrong preferred to describe the identity theory as ‘Central State Materialism’. Independently of Armstrong and Lewis, Medlin's central state materialism depended, as theirs did, on a causal analysis of concepts of mental states and processes. See Medlin 1967, and 1969 (including endnote 1).