Does "If X discovers that Y is Z" imply that Y is Z?

Solution 1:

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!"

Solution 2:

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.

Solution 3:

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.