Intentionality essentially involves the instantiation of semantic properties—such as having a meaning, an intension, a truth condition, satisfaction condition, extension or reference. Both linguistic utterances and mental states or events possess intentionality. According to physicalists, if intentionality is real, it must supervene on the physical. That is, physicalists hold that Semantic Supervenience thesis is true:

Semantic Supervenience
(PT ⊃ S)

Here, ‘’ is the metaphysical necessity operator, ‘⊃’ is the material conditional, P is a statement of all of the physical truths, T is a ‘that’s all’ statement to the effect that there is nothing more than is needed to satisfy P, and S is an arbitrary semantic truth, such as that Smith believes that mangoes are in season at a certain time or that Jones’ utterance of ‘the lecturer’ in a certain context refers to Ned Block.
In this paper, I develop a semantic zombie argument against physicalism about intentionality which parallels David Chalmers’ influential zombie argument against physicalism about phenomenal consciousness. A semantic zombie is a physical duplicate of one of us who lacks intentionality. Whereas Smith believes at a certain time that mangoes are in season, her semantic zombie twin is in a state that is physically and functionally identical to hers, yet which lacks intentionality. Whereas Jones refers to Ned Block when she utters ‘the lecturer’ in a certain context, her twin makes a physically identical utterance under physically identical conditions, yet refers to nothing. A semantic zombie scenario is one in which PT & ~S is true. Following Chalmers, I will argue as follows:

1. PT & ~S is conceivable.
2. If PT & ~S is conceivable, then
PT & ~S is metaphysically possible.
3. If PT & ~S is metaphysically possible, then physicalism about intentionality is false.
4. Physicalism about intentionality is false.