 Bertrand Russell (1927, p. 382) held the view that physical theory can reveal only causal structure, or “formal properties” of matter, and that “by examining our percepts we obtain knowledge which is not purely formal as to the matter of our brains.” This idea is taken up sympathetically (with substantial reworking in a quantum mechanical context) by Lockwood (1993). Chalmers (1996) offered a useful discussion of the view (now known as “Russellian monism”), and expressed some sympathy for it — a sympathy which has increased in intervening years (see, e.g., Chalmers, 2010). Denis Robinson (1993), however, regards intrinsic similarity of fundamental physical entities as different from similarity of phenomenal properties.