I've been thinking of an enquiry, turning in my head, and as I couldn't get a satisfactory answer,or rather, people around me did not answer it confidently, I suspect the answers given by them. So I thought it would be the best choice to ask the question here, too. I know the normal usage of if clauses, but can we use simple past tense in the first part of the sentence when we want to indicate an event of the past, whose result is obscure, as we do it, using present perfect tense?

For instance, let's say " If Bob has not finished his duty, it will bring an enormous disgrace on his academic career". In this case, we don't know if Bob has already finished his duty. He might have finished it, or vice versa.

If we had said " If Bob didn't finish his duty, it will bring an enormous disgrace on his academic career", would it be correct in terms of both meaning and grammar, as well?

To tell the truth, I frequently see it being used in films but I think they don't much care about grammar, do they?

Anyhow, I hope someone will give a reliving answer to me

Thanks in advance :)

closed as off-topic by MetaEd, NVZ, TrevorD, tchrist, user180089 Jul 29 '16 at 19:21

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  • Questions which lack results of research are out of scope. For an introduction to the site, take the Tour. For help writing a good question, see How to Ask. – MetaEd Jul 22 '16 at 17:19
  • Those are both well-formed conditional sentences. Why don't you think they are? – Peter Shor Jul 22 '16 at 18:17
  • Because I couldn't find any source that states a structure like " if he did it, it will be great" can be used to indicate an event in the past, whose result is unknown, and gramatically correct. They always use the structure ,"if he has done it, it will be good" – Nostradamus Jul 22 '16 at 18:40

I'm not entirely sure I understand what you are trying to determine--whether one sentence is more correct than the other as the expression of a particular conceit, or if they are each legitimate in their own right as the articulation of separate concepts. I will say this: each sentence IS grammatically correct, but they also reflect separate meanings.

Present in each are two certainties: first, if Bob should fail to "finish his duties, it will bring..."; and second, we do know not whether in fact he has fulfilled these these duties (your question seems to suggest that the certainty of this uncertainty is only present in your first example, when it is actually present in both).

The qualitative difference in meaning of your two examples is specifically situated in the present vs. past iterations of "has not" vs. "did not." In the case of "has not," it remains unknown whether Bob has finished his duties, but the implication is that if he hasn't (yet) it would be in his best interest to do so; i.e., there is still opportunity to do so.

In the case of "did not," we still do not know if he has finished his duties, but in the event that he hasn't, he will necessarily face the repercussions mentioned in the second half of the sentence, because the window of opportunity has indeed closed.

Hence, both sentences are grammatically correct, but indicate two very different set of circumstances for Bob!

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