Yet the naturalist cannot deny that there is determinate reference. The arguments of the philosophers, the observational reports of the sciences, and the equations of the mathematicians must have determinate meanings. Otherwise, science is impossible, and the case for naturalism collapses.
Therefore, if naturalism is true, the very things that are supposed to support it, such as argument and reason, aren't real. Only in a universe where the marks of the mental are metaphysically fundamental are these things possible.