Materialism is the name given to a family of doctrines concerning the nature of the world that give to matter a primary position and accord to mind (or spirit) a secondary, dependent reality or even none at all. Extreme materialism asserts that the real world is spatiotemporal and consists of material things and nothing else, with two important qualifications: first, space and time, or space-time, must also be included if these are realities rather than mere systems of relations, for they are not material things in any straightforward sense. Second, materialism is fundamentally a doctrine concerning the character of the concrete natural world we inhabit, and it is probably best to set to one side controversies over abstract entities such as numbers, or geometric figures, or the relations of entailment and contradiction studied in logic. A strictly extreme materialism would undertake to show that, to the extent that...