Future time clauses and Present Perfect

[Natalia]

Thank you. It's all much clearer now.

1. There's one sentence I forgot to add, namely: "I'd like to finish it before it has got dark." But I suppose, it's kind of smiliar to the sentence "Before he has sat down, he should wash his hands", where the present perfect may seem awkward, and the present simple would work better. Am I right?
2. Also, can you please provide an explanation why "have been" cannot be used in the sentence: "I won't let you stay out until you have been sixteen"?

[Daniel]

"I'd like to finish it before it has got dark."

Nothing specifically wrong with constructing a sentence like that, just not natural, probably because it's not necessary: "before" already has a similar sense to the perfective.

"I won't let you stay out until you have been sixteen"?

Again, nothing wrong with constructing that sentence, but it's very odd. It would mean "I don't trust you to make good decisions until you have had the experience of being sixteen years old". I would interpret that as saying you can't do it until you're 17. Or maybe that after your birthday experience, you are now wiser? It just doesn't make any sense in context. It would be fine structurally to replace it with something more relevant, like "Don't say that again until you've been in my shoes" (a common idiom meaning "until you've seen things from my perspective).

[Natalia]

Ok, I see. Personally, I'd use the present simple in the examples I provided, however, the students I'm teaching tend to oversue the present perfect in future time clauses, and sometimes I'm not sure wheteher I should correct them or just say that, for example, the present perfect is not necessary and the present simple is totally fine (obviously it all depends on the sentence). What do you think? As far as I can gather from your comments, the problem is not in grammar but rather in the fact whether a sentence t sounds logical/natural or not.

So just to be sure: Sentences like 'Before he has sat down, he should wash his hands" or "I'd like to finish it before it has got dark" are correct grammatically, but they would sound more natural with the present simple. Is that right?

[Daniel]

Usually, you can just use the simple present. That's one reason that sometimes the perfective forms can sound odd. But it's complicated, so I can't give you a general answer.

So just to be sure: Sentences like 'Before he has sat down, he should wash his hands" or "I'd like to finish it before it has got dark" are correct grammatically, but they would sound more natural with the present simple. Is that right?

Yes, structurally possible, but not something a native speaker would say. (If the emphasis really is on the completion of the event, you could try to use those, especially if you emphasize it with "just" for example, but the frequency would probably be less than 1% compared to the simple forms.)