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Related Question: Entailment/Presupposition in if-clause.

Consider the sentence "If John discovers that Mary is in New York, he will get angry." Does this imply that Mary is in New York now? Is "discovers" a counterfactual in present tense, only meaningful if John could now discover that Mary is in New York?

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In my opinion it does not say (one way or the other) whether Mary is now in New York. – GEdgar Oct 24 '11 at 1:07
I think it's more likely than not that she is, even if there's no other context to support the proposition. But when we say a particular phrasing implies something, we usually mean strongly implies. In this case the phrasing itself doesn't carry a strong implication, but I suggest it would normally only be used in contexts where the the likelihood (or otherwise) is already known to the hearer/reader. – FumbleFingers Oct 24 '11 at 2:14
If you wanted it to imply that Mary is in New York, you could say finds out. – user11550 Oct 24 '11 at 2:27
@Mahnax, that's silly. Replacing discovers with finds out does't change the ambiguity of the sentence at all. – Sam Oct 24 '11 at 6:51
@Sam, I disagree. Generally, if I say something like "If Bryan's mother finds out that he smokes, she'll kill him," it implies that Bryan does, in fact, smoke. – user11550 Oct 24 '11 at 14:41
up vote 9 down vote accepted

I think it all depends on context.

If John discovers life on Mars, he will be famous.

If John discovers that Mary is in New York, he will be mad.

Grammatically these two sentences may be the same, but contextually I think their meanings are very different.

Certainly the first does not imply anything about whether there actually is life on Mars or not. The sentence works either way.

The second sentence, on the other hand, does imply that the speaker believes Mary is in New York. Otherwise it just doesn't make sense to say it.

Whether Mary actually is in New York is a whole other matter :)

"If John discovers that Mary is in New York, he will be mad."

"Whatever do you mean? I just saw her five minutes ago!"

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I don't think the speaker actually has to believe Mary is in New York at the moment of the utterance - that's certainly possible, but suppose we're talking about our plans for lunch tomorrow. A: "Let's have the whole gang meet up!" B: "Oh, but how will we cover for Mary? If John discovers that Mary is in New York, he'll be angry." In this dialogue, B need only believe that Mary will be in New York tomorrow, when John could discover that fact; B could be unaware of Mary's location today, or be sure that she is somewhere else. – aedia λ Oct 24 '11 at 2:52
You're right. I didn't mean to imply he believed Mary was in New York at that moment, just that he believed Mary was in New York in whatever context he was referring to. – Lynn Oct 24 '11 at 3:02
Perhaps the context is that Mary has gone missing. The speaker does not know where she is, only that John has forbidden her to go to New York. – z7sg Ѫ Oct 24 '11 at 10:14

The logical semantics of the utterance:

If X discovers that Y, then Z

doesn't entail anything other than A implies Z if A is 'X discovers Y' (that's the accepted semantics of material implication).

However, pragmatically, saying this leads the listener to believe that Y is the case (in your example that Mary actually is in New York). That is, if someone told you this, you would be greatly annoyed if you found out -Y, that Mary was not in New York. The context is the usual if Mary was not in New York, then you just wouldn't say it the positive way.

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No it does not.

  • If John discovers that all perfect numbers are even, he will be momentarily famous in mathematics
  • If John discovers that at least one perfect number is odd, he will be momentarily famous in mathematics

can both be true at the same time without implying anything about the existence of odd perfect numbers.

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Consider a simpler sentence: "If John sees Mary smile, he will smile." Its form is parallel to that of your example, but for this sentence it is more obvious that the sentence is not a counterfactual conditional, which I think it would have to be to support the implication you ask about, but instead is an indicative conditional.

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The corresponding form should be "If John sees Mary is smiling, he will smile". Then we can meaningfully ask whether Mary is in fact smiling. And I agree with @Mitch that in the abscence of any other context, the implication of such a statement is that Mary really is smiling - the main uncertainty is whether John will see this or not. – FumbleFingers Oct 24 '11 at 2:19

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