Title: Cognitive Synonymy: a Dead Parrot?

Abstract:

Sentences φ and ψ are cognitive synonyms for one when they play the same role in one’s cognitive life: what one understands given either, one does, given the other; what one concludes (deductively, abductively, inductively, etc.) supposing either, one does, supposing the other; one would revise one’s beliefs in the same way after learning either; etc.

The notion is pervasive in linguistic and philosophical semantics, cogpsi, and AI – but elusive: it’s bound to be hyperintensional, but excessive fine-graining, e.g., by indiscriminate use of ‘open’ impossible worlds, would trivialize it and there are independent reasons for some coarse-graining. It should be sensitive to subject matters and conceptual limitations, but this stands in the way of a natural algebra: even non-distributive or non-modular lattices won’t do.

Besides, a cognitively adequate individuation of content may be intransitive due to ‘dead parrot’ series: sequences φ1, …, φn where adjacent φi,φj are cognitive synonyms for one while φ1 and φn are not. But finding an intransitive account is hard: Fregean equipollence won’t do and an impossibility result by Leitgeb shows that it wouldn’t satisfy a minimal compositionality principle . Sed contra, there are reasons for transitivity, too (from substitutivity salva veritate, non-mononotonicity, and uniformity principles).

In spite of this mess, we come up with a formal semantics capturing this whole jumble of desiderata, thereby giving evidence that the notion is coherent. We then re-assess dead parrot cases in its light.