Entailment/Presupposition in if-clause

Question

In our semantics class we were arguing about the exercise 3.(7) from page 33 in Chierchia et al.:

What relationship holds between the sentences in the following example?:

a) "If John discovers that Mary is in New York, he will get angry."

b) "Mary is in New York"

Is there any Entailment or Presupposition between the sentences?

The two controversial positions were basically "for the verb discover to make sense she indeed has to be in New York" vs. "as the discovery is hypothetically and might never happen we can not know, if she is in New York or not".

Does anybody have a convincing answer to this?

Answer 1

As long as the use of the term "discovery" indicates an actual discovery, then if the antecedent of the first sentence a) "John discovers Mary is in New York", then it follows that Mary is in New York. But, this is strictly speaking not a relationship between the sentences, but only between the antecedent of the first sentence and the second sentence. So, I don't see how the first sentence entails the second, and any claimed entailment has quite a case to make. Also, b), does not entail a), since Mary might exist in New York and stand undiscovered by John.

Answer 2

I can see how this is a tricky one. The problem lies with linguistics and English language usage. At first glance, it appears that (A) neither entails nor presupposes (B), because Mary could very well be in New York at some point in time but that doesn't necessarily mean she is there now. Specifically, the "if"—as Doug Spoonwood points out—can be used to imply that the following clause may or may not be true. The trick is that the same sentence in English can also be used to imply the current state of something. For example, if I were to say, "If my mom found out I am not really going to school, she would be angry", I would be intentionally implying that I am not really going to school right now . Likewise, the statement "If John discovers that Mary is in New York, he will get angry" can be used to imply that Mary is actually in New York.

I think the key word here is "discovers", specifically present tense and not past or future tense. That essentially implies that Mary is in fact—right now, presently—in New York. As I summarized in a comment below, for this work problem in a basic textbook, I think it's appropriate that we infer the least implications, i.e., not include an in the future implication as a possible interpretation of the original premise. I think if the book authors wanted to write "in the future" they probably would have, and it would have made the answer clearcut (i.e., there would be no entailments). But the fact that they left it out suggests either they wanted the opposite (an entailment such that A entails B), or they wanted everyone to be confused. As pernicious as some school textbook authors may seem to be, I think it's reasonable we can assume they did not intend the latter... :P

Thus, I believe that fairest answer is that (A) presupposes (B).