Sentences vs. Propositions

Question 1

Explain the Different Sentences, Same Meanings objection for the Referential Theory of Meaning

Answer 1

1. Suppose that speakers a, b, and c are each entertaining a thought which in their native language is expressed by (13), (14), and (15) respectively.
   (13) The grass is green.
   (14) Græsset er grønt.
   (15) Das grass is grün.
   Intuitively it seems clear that a, b, and c are entertaining the same thought.
   But if sentences are the objects of thought, then since these sentences are different, how do we explain that a, b, and c are thinking the same thing?
2. Suppose that a and b both utter the sentence in (16).
   (16) I’m tired.
   Clearly a and b have said different things. In particular, a has said that a is tired, and b has said that b is tired.
   But if sentences are the fundamental bearers of meaning, then a and b should have said the same thing—and clearly they have not.
   This suggests that a sentence in isolation cannot be the fundamental bearer of a truth value — after all, what would the truth value of (16) be?
3. Consider the sentences below:
   (17) Every renate is a product of evolution.
   (18) Every cordate is a product of evolution.
   The predicates ‘renate’ (creature with a kidney) and ‘cordate’ (creature with a heart) are co-referential (also called co-extensional).
   That is: {x ∣ x is a renate} = {x ∣ x is a cordate}
   Given this, if the meaning of the sentence is simply its truth conditions, (17) and (18) are predicted to have the same meaning. But this seems incorrect.
4. This problem becomes even clearer if we consider belief reports, i.e. sentences that report beliefs.
   (19) Bertrand believes that every renate is a product of evolution.
   (20) Bertrand believes that every cordate is a product of evolution.
   It seems obvious that (19) could be true while (20) is false. After all, Bertrand might not even know what a heart is.