The worst that can happen is that he fail/fails/would fail/will fail the exam.
Which of these is (or are) correct? In Spanish, the subjunctive mood would be used, is the case similar in English?
The worst that can happen is that he fail/fails/would fail/will fail the exam.
The subjunctive fail sounds a bit off to me here. As a subjunctive clause, that he fail the exam is flawless, but in English, the subjunctive is most often used to convey a request or command: She insisted that he give that student the failing grade he deserved. (The subjunctive is also used in a few other cases, none of which apply here.)
The declarative fails and will fail strike me as acceptable but informal. Would fail is all right. Should fail/can fail/could fail are all acceptable too. Should fail is a bit formal.
"fails" is correct. The sentence then means that the exam is in the future and he might fail.
"fail" is wrong in this instance since the subject is singular, and fail would be used for a plural subject.
"would fail" can not be used in this case. It would be used in a situation like: He didn't want to try because he thought he would fail.
"will fail" I am unsure about. But I think it comes down to "tense simplification" Michael Swan's Practical English Usage:
If the main verb of a sentence makes it clear what kind of time the speaker is talking about, it is not always necessary for the same time to be indicated again in subordinate clauses. ... And: Verbs in subordinate clauses are often simpler in form than verbs in main clauses - for example present instead of future, simple past instead of would + infinitive, simple past instead of past perfect. You'll find Coca-Cola wherever you go. NOT: wherever you will go.
The worst that can happen is that he fail the exam.
I'm an English major. Yes, unlike the others above, I agree with you. Just like in Spanish, the subjunctive is used here, too, in English. You could also use a modal here like "will" with "fail". The subjunctive is very formal here, though. There are many places in English sentences wherein the subjunctive should be used, but isn't. Here is one.
Example: The worst that can happen is that he be found guilty.
It's difficult to tell sometimes. I like to use "be" to see whether the subjunctive is correct. Cheers!!!!
There are two solutions to your problem. Strictly speaking, the best answer is
The worst that can happen is that he will fail the exam.
However, the subjunctive construction can also work, although it will certainly caused eyebrows to be raised in your direction:
The worst that can happen is that he fail the exam.
Some would argue that the subjunctive is no longer applicable in this construction in English; I like it, but I'm not prepared to argue very vigorously in its defense. The remaining version (the indicative “fails”) is analogous to saying “If I was a rich man”: certainly acceptable English, but not strictly correct.