Functionalism about Truth and the Metaphysics of Reduction

Functionalism about truth is the view that truth is an explanatorily significant but multiply-realizable property. According to this view the properties that realize truth vary from domain to domain, but the property of truth is a single, higher-order, domain insensitive property. We argue that this view faces a challenge similar to the one that Jaegwon Kim laid out for the multiple realization thesis. The challenge is that the higher-order property of truth is equivalent to an explanatorily idle disjunction of its realization bases. This consequence undermines the alethic functionalists' non-deflationary ambitions. A plausible response to Kim's argument fails to carry over to alethic functionalism on account of significant differences between alethic functionalism and psychological functionalism. Lynch's revised view in his book Truth as One and Many (2009) fails to answer our challenge. The upshot is that, while mental functionalism may survive Kim's argument, it mortally wounds functionalism about truth.