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l saw this sentence on my text book

would you like a cup of tea before______

and the only answer is “you go/leave”.l wonder why can't use “before you have gone” here.

The other question in this book:

can I have a newspaper when_____(you read)

Can you let me know as soon as_____(you dicide)

I think it’ll be better when_____(new road,finish)

They can both use “do” and “have done”.

So what time we can use both of them which have the same meaning？

and what time we can only use the former or the later？

could you show me some examples？

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    Why do you think they have the same meaning?
    – gotube ♦
    Commented Aug 24, 2022 at 13:33
  • 2
    I cannot think of any case where either "when somebody do" or "when somebody have done" is ever correct. Only "when somebody" does or has done is correct. Did you see either one used somewhere? If so, please post the entire sentence and where you found it. (Also, the word is somebody, not sb. Sb is an abbreviation only used in dictionaries.)
    – stangdon
    Commented Aug 24, 2022 at 14:23
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    Please show us some examples.
    – Jeffrey Carney
    Commented Aug 24, 2022 at 14:43

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The essential difference is in whether the action is starting or ongoing (do) or is finished (have done).

Can I have the newspaper when you've read it?

Only "have read" makes sense here, since you probably mean you want the newspaper after the other person finishes reading it. If it were "read", it would mean you want it while they simultaneously read it.

Can you let me know as soon as you decide? / as soon as you've decided?

Either one is acceptable, because "decide" is not continuous, but instantaneous — starting and stopping are the same thing. I would say they're about equally likely as well, though the present perfect somehow strikes me as more polite / formal.

I think the commute will be better when they they finish / when they've finished the new road.

For the same reason as "decide", either one is acceptable. But if you were to use "build" instead of "finish", then you would have to use the present perfect, since the present would mean that they commute will improve simultaneously with the road being built, which is unlikely.

Would you like a cup of tea before you leave / go?

Here "before you've left" or "before you've gone" would not work because it opens the possibility that they have a cup of tea between starting to leave and finishing leaving, which makes very little sense. Indeed, if you understand "leave" as an instantaneous verb like "decide", then that interval of time implied by the present perfect doesn't exist.

I'm not sure if this logic would hold up in every case, but it seems like a good fit here.

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