A true sentence like ‘John is here in this room’, and its Twin Earth counterpart, express different propositions, since they are about distinct people. And that means that propositions sometimes constitutively involve particular external things that they are about.
If someone says, as you just tried to do, "'Vulcan exists' expresses a true proposition", then the proposition expressed by that sentence, if, as with many other sentences said from time to time, including the one I am now writing, has never before in the history of the world been produced, then it now exists, in the sense that it is a concrete individual (i.e., the product of a concrete individual act) that came into the world at a particular spatiotemporal point. So, the complex sentence that I just wrote is (probably) a unique individual that has just come into the world, and the same is true of the proposition expressed by it (although in understanding it you the reader need to produce an equivalent); but before that it was among the open-ended number of possible sentences/propositions determined by the generative principles of the categories and propositional schemata of the language system (in this case English) used to express it. So the generative rules of the linguistic system (I am using the term 'generative' in a sense different from Chomsky's, to refer to a structure which creates its own instances, a property common to all action schemata) determine an open-ended number of possible instances, and, for referential categories, an open-ended number of possible referents out in the world (the denotation of the category, as opposed to the extension, which term refers to the concrete instances of the category in use of the language). Instantiation of the categories in a concrete act of language use makes the possibilities actual. (You do use the term "instantiation above.) I see that philosophers usually do not pay much attention to natural language systems (Dummett, e.g., in Origins of Analytic Philosophy, is an exception), puzzling more about the individual instances and the "truth" relation, but any properties of particular propositions expressed by particular sentences in context are determined, made possible, by the properties of the preexisting categories of the language system.
BTW, wrt the importance of norms of linguistic systems, an interesting thing to do with Putnam's "Twin Earth" thought experiment is to wonder what would happen if the previously separated speech communities were to come together and combine into a single unified speech community.
Sorry to bother you; I must seem like a crank. (I'm not a philosopher, just a descriptive linguist who loves philosophy, so that's probably a source for the weirdness.) But these are the thoughts I had in response to your now old post, so thank you for that. I promise I will not write any further comments.
BTW, you don't need to go to Twin Earth for examples.
E.g., two utterances of sentences that are formally completely equivalent, e.g., "Sally didn't sautee the vegetables, she boiled them." could be uttered in two different speech situations, one where the proposition expressed is true, and the other where an equivalent proposition, as intended or interpreted, is false. The difference is in the referent of the proposition, the factual differences in the situation described, which can be independently identified. To say, as Frege did, that the referent of a proposition is a truth value gives us no help in explaining why the two propositions equivalent in message differ in truth value. (At least Frege extended the notion of reference to propositions; what he lacked was an alternative way of describing the situation referred to by the proposition.)
I'm prepared to defend and clarify as an empirical, descriptive claim, that propositions, i.e., what is expressed (as intended by the speaker, understood by the hearer as a possible interpretation and arrived at by a critique of the linguistic act by an observer), are logical individuals, instances of the generative categories and propositional schemata of the natural language system that make them possible, in the same way that concrete purposeful actions are individuals made possible by general action schemata. A proposition is a product of an act of meaning-creation (or meaning-production), an act distinct from the act of producing the expression (e.g., a sentence) that expresses it. (Actions, not objects (or their translational counterparts in model theories, sets) are the prototypical individuals.) One can compare individual propositions by noting the equivalences (and differences) between them and grouping them into equivalence classes for various purposes. What has objective existence out in the world are the categories (lexical, morphological) and propositional schemata of natural language systems, on the level of speech-community norms. (I say that what is used by speakers in acts of language use is, e.g., not sentences (also individuals), but categories.) This approach to the content expressed by linguistic expressions (or "thoughts" in Frege's sense) seems to allow the solution of a lot of traditional philosophical problems, including Putnam's persistent question, "How does language hook on to the world?"
This is just a little bit of a larger context of ideas that are no doubt required for this to make sense, but I would appreciate any critique you might have of this idea, and any observations you might have of the possibly many ways I am going wrong. I am aware that the above view differs from the traditional view of what are called "propositions" in philosophy, where they seem to have a categorical structure (two instances are somehow "the same" proposition) and exist perhaps in some Platonic realm. And BTW, why have you gone for so long without posting?
If someone says, as you just tried to do, "'Vulcan exists' expresses a true proposition", then the proposition expressed by that sentence, if, as with many other sentences said from time to time, including the one I am now writing, has never before in the history of the world been produced, then it now exists, in the sense that it is a concrete individual (i.e., the product of a concrete individual act) that came into the world at a particular spatiotemporal point. So, the complex sentence that I just wrote is (probably) a unique individual that has just come into the world, and the same is true of the proposition expressed by it (although in understanding it you the reader need to produce an equivalent); but before that it was among the open-ended number of possible sentences/propositions determined by the generative principles of the categories and propositional schemata of the language system (in this case English) used to express it. So the generative rules of the linguistic system (I am using the term 'generative' in a sense different from Chomsky's, to refer to a structure which creates its own instances, a property common to all action schemata) determine an open-ended number of possible instances, and, for referential categories, an open-ended number of possible referents out in the world (the denotation of the category, as opposed to the extension, which term refers to the concrete instances of the category in use of the language). Instantiation of the categories in a concrete act of language use makes the possibilities actual. (You do use the term "instantiation above.) I see that philosophers usually do not pay much attention to natural language systems (Dummett, e.g., in Origins of Analytic Philosophy, is an exception), puzzling more about the individual instances and the "truth" relation, but any properties of particular propositions expressed by particular sentences in context are determined, made possible, by the properties of the preexisting categories of the language system.
BTW, wrt the importance of norms of linguistic systems, an interesting thing to do with Putnam's "Twin Earth" thought experiment is to wonder what would happen if the previously separated speech communities were to come together and combine into a single unified speech community.
Sorry to bother you; I must seem like a crank. (I'm not a philosopher, just a descriptive linguist who loves philosophy, so that's probably a source for the weirdness.) But these are the thoughts I had in response to your now old post, so thank you for that. I promise I will not write any further comments.
BTW, you don't need to go to Twin Earth for examples.
E.g., two utterances of sentences that are formally completely equivalent, e.g., "Sally didn't sautee the vegetables, she boiled them." could be uttered in two different speech situations, one where the proposition expressed is true, and the other where an equivalent proposition, as intended or interpreted, is false. The difference is in the referent of the proposition, the factual differences in the situation described, which can be independently identified. To say, as Frege did, that the referent of a proposition is a truth value gives us no help in explaining why the two propositions equivalent in message differ in truth value. (At least Frege extended the notion of reference to propositions; what he lacked was an alternative way of describing the situation referred to by the proposition.)
I'm prepared to defend and clarify as an empirical, descriptive claim, that propositions, i.e., what is expressed (as intended by the speaker, understood by the hearer as a possible interpretation and arrived at by a critique of the linguistic act by an observer), are logical individuals, instances of the generative categories and propositional schemata of the natural language system that make them possible, in the same way that concrete purposeful actions are individuals made possible by general action schemata. A proposition is a product of an act of meaning-creation (or meaning-production), an act distinct from the act of producing the expression (e.g., a sentence) that expresses it. (Actions, not objects (or their translational counterparts in model theories, sets) are the prototypical individuals.) One can compare individual propositions by noting the equivalences (and differences) between them and grouping them into equivalence classes for various purposes. What has objective existence out in the world are the categories (lexical, morphological) and propositional schemata of natural language systems, on the level of speech-community norms. (I say that what is used by speakers in acts of language use is, e.g., not sentences (also individuals), but categories.) This approach to the content expressed by linguistic expressions (or "thoughts" in Frege's sense) seems to allow the solution of a lot of traditional philosophical problems, including Putnam's persistent question, "How does language hook on to the world?"
This is just a little bit of a larger context of ideas that are no doubt required for this to make sense, but I would appreciate any critique you might have of this idea, and any observations you might have of the possibly many ways I am going wrong. I am aware that the above view differs from the traditional view of what are called "propositions" in philosophy, where they seem to have a categorical structure (two instances are somehow "the same" proposition) and exist perhaps in some Platonic realm. And BTW, why have you gone for so long without posting?