We distinguish mental states with different contents all the time in everyday life. But what distinguishes (or, better, to individuates) their contents?

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We use propositions to individuate the contents of mental states. But what are propositions?

Reading (optional):

• McGrath, Matthew and Devin Frank, "Propositions", The Stanford Encyclopedia of Philosophy (Spring 2018 Edition), Edward N. Zalta (ed.), https://plato.stanford.edu/archives/spr2018/entries/propositions/
• King, Jeffrey C. ‘Structured Propositions’. In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Summer 2019. Metaphysics Research Lab, Stanford University, 2019. https://plato.stanford.edu/archives/sum2019/entries/propositions-structured/

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What distinguishes the contents of mental states? We have seen that the answer is: propositions. Propositions stand to mental states roughly as numbers stand to weights or temperatures. But what kind of propositions could we use to distinguish the contents of mental states? We already saw that Lewisian propositions (sets of possible worlds) are not so useful. Frege’s argument about sense and reference establishes that Russellian propositions are likewise not sufficient to make all the distinctions between contents that we need.

Reading (optional):

• Frege, G. (1980). Letter to jourdain. In Kaal, Hans (trans), Philosophical and mathematical correspondence, pages 78–80. (Find the letter online by searching for the terms ‘frege’, ’etna’ and ‘ateb’.)
• Section 3.1.1 and the first paragraph of Section 3.2 of Zalta, Edward N., "Gottlob Frege", The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.)

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Senses cannot be descriptions. At least not if we are to use Fregean propositions to distinguish the contents of mental states. For if senses were descriptions, we would be forced to use the same Fregean proposition to capture the contents of two non-equivalent thoughts.

Reading (optional):

• Kripke, S. A. (1980). Naming and necessity. Library of philosophy and logic. Blackwell: Oxford, rev. and enlarged edition.
• §2.1 of Michaelson, Eliot, and Marga Reimer. ‘Reference’. In The Stanford Encyclopedia of Philosophy, edited by Edward N. Zalta, Spring 2019. Metaphysics Research Lab, Stanford University, 2019. https://plato.stanford.edu/archives/spr2019/entries/reference/.

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We have a convincing argument for postulating senses. But we also have a problem. ‘[A]ll that anyone has been able to think of is that different [senses] are [...] descriptions’ (Campbell, 2011 p. 340) And yet, as we have seen, senses cannot be descrpitions (Kripke, 1980).

Reading (optional):

• Kripke, S. A. (1980). Naming and necessity. Library of philosophy and logic. Blackwell: Oxford, rev. and enlarged edition.
• Campbell, J. (2011). Visual Attention and the Epistemic Role of Consciousness. In Mole, C., Smithies, D., and Wu, W., editors, Attention: Philosophical and Psychological Essays, page 323. Oxford University Press.