Dialogue

Deleet:

Reality changes all the time such that the truth value of propositions change. For instance, the proposition “Deleet is alive” is true right now but it will become false when I die. Similarly, the proposition “John F. Kennedy is alive” is false because reality has changed and he died. When he was alive, the proposition was true. Before he was born the proposition was also false.

Ken:

The proposition that Deleet is alive in 2009 is true 1,000 years ago, and will be true 1,000 years hence. All you have to do is to insert the missing time parameter. One true, always true. Reality doesn’t change, what we say about it does.

Deleet:

It was my intention to leave the time parameter out. In this way the truth of the proposition changes when reality changes (correspondence theory of truth).

Reality; the objective world changes. I will not discuss that here.

Ken:

Yes. Your leaving it out is why you think that truth changes with time. You should put it back in so that you will not think that.

Deleet:

My view is that your conflating two propositions: “Subject S is alive” and “Subject S is alive at time t”. These are not identical; They are not the same proposition. They sometimes share truth values and they sometimes don’t.

Ken:

But the first is an incomplete proposition, which is why you think that truth is temporal.
It is like the difference between:

1. Dogs are mammals, and,
2. All dogs are mammals.

1 and 2 are not different propositions. 2 is just a complete proposition, and 1 is incomplete.
You would not say that Dogs are mammal is a vague fact because the sentence, “Dogs are mammals” is incomplete, would you?

Deleet:

1.
There is no such thing as an incomplete proposition. A proposition is “[w]hat is conveyed by a declarative sentence […]”, source.

There are incomplete statements in the sense that the statements do not fully express the meaning they was intended to convey and so we fill in the rest of the meaning by interpretation. Your example with dogs is an example of us filling in: (1) can convey the meaning of “All dogs are mammals.” (2) or “the meaning of “Some dogs are mammals.”.

2.
Neither (1) or (2) are really propositions although in practice we treat declarative statements as propositions. They are not. The meaning they convey are. (1) does not convey any specific proposition because it can, depending on interpretation, have multiple meanings; (1) is ambiguous. (2) conveys a single proposition.

3.
I hold that my two statements (3) “Subject S is alive” and (4) “Subject S is alive at time t” are specific proposition conveying statements i.e. they convey precisely one proposition.

Ken:

Only if (3) is uttered at time t, when, I suppose, it will be construed as (4). I don’t know how you use, “statement”, “proposition”, or “sentence”. But you see what I mean. The time of the utterance allows us to understand what the complete statement is, just as the context will allow us to construe “Dogs are animals” as, “All dogs are animals”, but “Dogs are brown” as, “Some dogs are brown”, since we’ll assume that the speaker has the same knowledge as we do in the absence of any evidence to the contrary.

Deleet:

1.
The general assumption is to insert “at time t and t is now”. This still makes (3) and (4) different. In (4) t does not have to be now; It could be 1960.

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Source.

Propositions and time

A time parameter ≡ the part of a proposition-conveying sentence that conveys information about the time. E.g. “The Earth is round in 1960.“. The time parameter is the text marked with italic.

Ken seems to think that all truths are timeless; independent of time. I agree that some truths are timeless. All truths that have a set; non-relative time parameter (e.g. “in 1950”) are true no matter what the time is now. However, not all truths have a set time parameter. Normally when one makes an assertion, it is missing the time parameter. We interpreted it as having a present time parameter–“now”. E.g. when one says “The Earth is round”, we interpreted the proposition-conveying sentence to be ” The Earth is round now“.