Let us hypothetically assume materialism, that all possibilities are completely described by physical specification. Under this assumption, I do not believe that any moral statements can be justified. In a materialistic universe, all possibilities are adequately described physically; therefore, a moral statement would be a reason for preferring one physical arrangement to another. On what grounds could one make such a claim? The preference could not refer to any non-physical standard, such as symmetry or order, for such a standard, if true, would be a true non-physical statement and thus contradict the assumed materialism. The standard cannot be contained in some portion of the physical universe, for rules for mapping states to prescriptions are without limit, and the rule used would then become a non-physical statement.1 The standard could not be correspondence of the whole universe to itself, for that is tautologically true. Therefore, no standard is consistent with materialism, whether not founded on any physical facts, on some facts, or on all. Consequently, no preference among possible configurations of atoms can be justified.
But, following our original assumption of materialism, only configurations of atoms exist, and thus all things, including thoughts, are solely configurations of atoms. Thus, within a materialistic universe, no belief is preferable to any other. Consequently, if materialism is true, the set of atoms corresponding to belief in materialism is in no way preferable to that corresponding to disbelief, even though the former is true and the latter false: the consistent materialist cannot prefer truth to falsehood.
On the other hand we may consider the rule that belief in truth is better than belief in falsehood. This being a nonphysical fact, it is inconsistent with materialism. If it is true, then to believe it is better than to believe the contrary; if false, not. Thus, I conclude that belief in materialism is, even if logically consistent, irrational, for belief in the preferability of truth to falsehood is better than belief in materialism if true, but is not worse if false.
1: Thus we may dispense with attempts at materialistic egotism. Whence does the materialist determine that the arbitrary group of atoms he considers himself are preferable as a normative standard?