|Geach, Peter T.
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Proposition/GeachVs: no abstract entity - here only used under protest: the following is generally accepted about propositions:
(i) any unambiguous statement expresses exactly one proposition -
(ii) synonymous propositions have the same meaning -
(iii) a "that-clause" denotes what is expressed by "p" -
(iv) "The proposition that p" and the "that-clause" "that p" are synonymous terms of the proposition -
(v) "The proposition expressed by Qp", whereby Qp is a quotation of p, denotes - the same proposition as "the proposition that p" - one does not
(iv) need to understand that "that p" can always be replaced by "the proposition that p"
From the above theses follows that every oratio obliqua is always translatable into oratio recta - James considers the proposition that is expressed by "There are Marsmen ...", with dread- GeachVs: but this cannot stop us to simply abbreviate : "has this fear" - but not a criterion for synonymy.
Necessary/Proposition/Geach: if the that-clauses are designations of abstract entities, then these abstract entities cannot be propositions. - Reason: reciprocal strict implication is not an identity criterion for propositions - but: it is a sufficient condition in the modal logic for the replaceability salva veritate of subsets. We would therefore have a criterion for the identity of such entities, which are designated by such subsets - but no need for such "designata".
Proposition/Geach: cheap metaphysics: easy to ask: "But what are propositions" like "But what are numbers?" The reference e.g. to know the identity of a number means to be able to identify numbers and to keep them apart - and that means, vice versa, to know the truth conditions of a sentence. - We could make a theory of propositions without knowing what propositions actually are - but reciprocal entailment for propositional equality does not work as a criterion for identity ((s) because intensional).
Definition Proposition/Terminology/Geach: something that is put forward to be considered - (no assertion, a suggestion!) - "sentence" is actually grammatical. I prefer "Proposition". - Propositions need not be asserted.
Logic Matters Oxford 1972