Future Perfect and 1st conditional

Question

Could you explain, please, the meaning of this sentence (under what circumstances can it be said?):

Rob will have passed the exam if he has studied enough.

Maybe, it will be easier to explain it if you compare the first example with the following one:

Rob will pass the exam if he has studied enough.

Is it correct that the first example describes possibility after the exam, but the second one - before the exam? Could you explain it more clearly, please?

If we use First Conditional for a future situation, I can't understand how "the first example describes possibility after the exam" because it means that the exam was already in the past. Is it correct to use Future Perfect in this case? I'm confused.

Answer 1

I think you're on the right track. Let's take these in the opposite order in which you presented them.

Rob will pass the exam if he has studied enough.

This is speaking solely of the event of Rob passing the exam. The speaker is predicting that event (passing the exam) will occur if the condition (he has studied enough) is met.

Rob will have passed the exam if he has studied enough.

This is speaking of the state of things after an event. Without context, it sounds very bizarre. But let's add some context:

We want Rob to join our firm as a lawyer, starting next month. He still needs to take his qualification exam and wait for the results, though. Therefore, we're asking him to take it immediately, so that, by the time we want him to start the job, he will have passed the exam, assuming he has studied enough.

You'll see that this draws attention to some point in the future after the event. That is, the speaker predicts that at a point in the future (the start of the job), the event (passing the exam) will have occurred in the past.

You'll also notice that I changed "if he has studied enough" to ", assuming he has studied enough." That sounds more natural to me.

Here's another, somewhat different use of "will have" that you should probably know about.

There's no point in going to the train station. The train will have already left by now.

The "will have" in this example is used to state a strong present assumption that the train left in the past. See also: https://www.grammaring.com/modals-to-express-assumption-will-should-ought-to

Answer 2

You do understand correctly. I think the part of the sentence containing the "condition" is confusing you, so let's leave it out for a second:

1. Rob will pass the exam tomorrow.
2. Rob will have passed the exam tomorrow.

We are saying this sentence today. Everything under discussion is in the future. The first sentence is in the simple future tense: Tomorrow, without doubt, Rob will take and pass the exam—let's say the exam ends at noon. The second sentence, then, talks about a later part of tomorrow, tomorrow afternoon. So, to your question: both sentences are being said before the exam; one talks about the possibility of the exam, and one talks specifically about the conditions after the exam.

Now, for the conditional phrase: if he has studied enough. Don't let this throw you; the tenses of the main part of the sentence are not dependent on it. It just so happens that this phrase speaks of studying that Rob has already done in the past, but that timeline is independent of the future tense of the rest of the sentence.

By the way, I find this page very helpful in sorting out conditionals (though it doesn't directly address this situation, a hypothetical future dependent on a past condition).