I have had some additional thoughts about this after discussing it with fast here.

First fast asks:

“You said, “a sentence is true [if and only if] it expresses exactly one proposition and that proposition is true. I don’t understand the reasoning behind the “exactly one” condition as you have worded it. An implication of what you said is that a sentence that expresses more than one proposition (hence, not exactly one proposition) is not true because you said, “if and ONLY if”, but I don’t see why you would think that.

[…]

Is it because if one of the propositions is false, then the sentence is both true and false and that’s a contradiction?”

I did reply to that in the thread but I think it deserves a longer reply.

First, yes, it is to avoid conflicts with bivalence about sentences, that is, for all sentences, a sentence is either true or false but not both. But then I realized that maybe one could drop bivalence about sentences but not drop it about propositions. Supposing that one drops bivalence about sentences, then one can adopt much broader truth-conditions of sentences:

A sentence is true iff it expresses a true proposition.

A sentence is false iff it expresses a false proposition.

However it is also possible to accept broader truth-conditions even keeping bivalence about sentences. One could just specify that all the propositions expressed by a sentence has to have the particular truth value. It doesn’t matter if it is one or more:

A sentence is true iff it expresses only true propositions.

A sentence is false iff it expresses only false propositions.

2 Responses

  • kzuit

    Hi Emil
    “a sentence is true if it expresses a true proposition”
    Is that more or less the same as
    “what you say is true if what can be understood from what you say is true”??
    For a novice in this area could you tell me what’s philosophically important in this? Will you go on and discuss then what true means?

    Rgds

    kzuit

    • Emil Kirkegaard

      Hi kzuit,

      I did not write “a sentence is true if it expresses a true proposition”. I wrote “A sentence is true iff it expresses a true proposition.”. “If” and “iff” do not mean the same. “Iff” is an abbreviation for “if and only if”.

      No, it does not mean more or less the same as what you wrote.

      I have no plans to discuss a theory of truth in the future and my blog is not aimed at complete novices at philosophy. You should pick up a textbook if you want to learn the basics. :)

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