How could it be that the following sentence is NOT a proposition?

Question

Consider the sentence "It might be dark outside". Is this a proposition? What sorts of arguments could you make that this sentence isn't a proposition?

Is it that it is making -- potentially -- a claim about the states of affairs of other worlds (as opposed to the actual world) and hence can't be a claim about the actual world and hence can't be a proposition? (Genuine question here).

Basically, I'm trying to understand the view which states "not all sentences have propositional semantics; indeed, many of them just express properties of attitudes".

Answer 1

A proposition is-equal any message that has a "truth value". Consider this sentence:

"It might be dark outside".

Does it have a "truth value"? If yes, then it's a proposition. If no, then it's not.

The first step is to identify the meaning of John's message. It's important to understand that the exact same words can have different meanings depending on context.

Consider this scenario:

Mary asks:

Is it dark outside?

John replies:

It might be dark outside.

whereby John meant:

It might be dark outside. Maybe it is. Maybe it isn't. I don't know.

then John is not making a claim regarding the "darkness of outside". He is claiming that he has no knowledge of the "darkness of outside". Since that has a truth value —could either be true xor false—, the message is a proposition; not a proposition regarding the "darkness of outside", but a proposition regarding John's (own) knowledge.

However, if John meant:

It might be dark outside. There is a chance that it is dark outside. (There is above zero probability that it is dark outside).

then John's message is a proposition regarding the "darkness of outside". It has a "truth value":

• It is true if there is above zero probability that it is dark outside.

• It is false if there is exactly zero probability —no chance— that it is dark outside.

• It must be either true or false.

If we tweak the scenario and change John's reply to:

It might be dark outside, but so what?

whereby John meant:

I don't care if it's dark outside. Why do I need to care?

then John's message is not proposition because it is a question and it can neither be true nor false.

Answer 2

Propositions are moves in a language game that intends to describe things. They have truth value, in the sense that what they propose is meant to be considered as an assertion describing reality. But there are other language-games, which are not primarily concerned with this task.

Statements of possibility are generally not informative. They are moves in the game of thinking itself, or in some sub-game about thinking, like auditing understanding. They inject a parameter over the range of possible worlds, and request that one's listener consider whether the parameter with possibility has been considered adequately. In doing so, they generally put you farther from certainty (correct or otherwise) rather than closer to it.

They are not even informative statements about alternative worlds. When would one say "It might be dark."? Not when one thinks this is information the listener does not have. If he did not know of this possibility, he would need a lot more information about the nature of light, in order to care. And any of that information would be more useful to contribute. Instead one says this when one thinks the plans so far do not adequately consider that dimension.

Since they do not cover descriptive ground, but instead open new ground, they do not contribute directly to understanding in the same way. So such statements do not play the role propositions are meant to fulfill. It is possible to interpret them as propositions, but doing so does not allow them to perform their intended function. If someone contributes "It might be dark." and your only response is to affirm the possibility, he has failed to communicate.

(Answering Pacerier's silly question, if Mary asks whether it is dark outside, and John replies that it might be, he is agreeing that he had not to that point considered whether or not it was, and whether it should have any effects. He might only be so agreeing in excessive politeness, if he is fairly sure it does not matter.)

Answer 3

I would say that the statement "It might be dark outside" is logically equivalent to the statement "It is either dark outside or it is not dark outside".

This is a tautological statement, i.e., a fact in the sense that it cannot be false.

Facts are not propositions.

EDIT

Following virmaior's comments below, I will attempt to justify / correct my answer.

One might argue that the equivalent form "It is either dark outside or it is not dark outside" is an instantiation of the second law of thought - i.e., the law of the excluded middle. As such, it would not be considered a proposition. This is because our laws of thought are given, and therefore not subject to a change of status.

Some statements may fulfil the definition of tautology, but at the same time possess other attributes which override their status as a tautology. For example, an instance of a law of thought or an axiom in disguise. They are redundancies or unwanted baggage that result from our methods of formalization. One might say they are artefacts. We begin with what we are given, and we then generate our propositions. We do not generate our laws of thought.

The term proposition has a meaning in general philosophy beyond that of propositional logic, and the wiki entry for proposition states that according to general use of the term, facts are not propositions.