Thread: Future Simple VS Future Perfect

Hi folks,

I have a question regarding the tenses...
What's the difference between:
1) By the evening I'll have done the work
2) By the evening I'll do the work

Also,
Is it correct to use Future Simple in the sentences below or only Perfect is correct?

By the time he comes back from prison she'll have graduated from university
By the time we arrive the most of coffee will have been drunk

Thanks in advance!

By the evening I'll have done the work = correct. When you say "by X time", you use future perfect. Don't say "by the evening I'll do the work".

Similarly with your other two examples - use future perfect. Also one minor correction:

Originally Posted by Mervin

By the time we arrive the most of the coffee will have been drunk

Demonic_Duck, thanks!

Hmm...for some reason my English teacher told me that By the evening I'll do the work is also acceptable...

Bear in mind that I'm not a qualified teacher, I'm just an ordinary English speaker, so it's possible your teacher knows more than me. It may be acceptable to use future simple, but it certainly looks less "native" to my eye.

Originally Posted by Mervin

Demonic_Duck, thanks!

Hmm...for some reason my English teacher told me that By the evening I'll do the work is also acceptable...

sounds odd, ungrammatical to me. I'm not sure what accepatable means, anything that conveys some sort of meaning may be acceptable, I guess.

"Ordinary" native speakers always beat non-native speaker teachers hands down. If a teacher says one thing about a language and a native speaker disagrees, go with the native speaker.

Also, "acceptable" in such a context usually means that a native speaker might consider it grammatically correct and even use the form, but not all native speakers might agree. Or it may be acceptable in certain situations or at certain levels of speech but not in others.

I disagree with "by the evening I'll do the work" being acceptable. But I'm not a native speaker of English. However, "by the evening" refers to the point in time by which some activity will have ended - then at the latest, or at some point in time before that. Therefore future perfect is used. "I'll do the work" implies that work will begin at a specific point in time. Therefore I feel that the two phrases disagree, one states a point in time when something is over while the other implies it will begin.

It's strange though, if you switch that sentence round ("I'll do the work by this evening") it sounds much more natural. Perhaps it's because it's like a promise here ("I promise you, I WILL do the work by this evening!")

On the other hand, if you switch around your second example like this, it doesn't work. "She'll graduate from university by the time he comes back from prison" still definitely sounds wrong.

Every time I think about the English language too much, it's like a massive mindf**k. I use the grammatical rules every single day, and yet I don't actually know what those rules are! Whenever I try to explain a grammar rule to a non-native English speaker, I feel like I'm rationalising the rule to myself more than explaining it to them.

All I can really say here is to always use perfect tenses when you're talking about "by X time". That way, you definitely won't go wrong

By the evening I'll have done the work

The way I see it this sentence is telling you something about this evening. Maybe you are making plans for the evening or are anticipating how you'll be feeling then. It means pretty much the same as
(By) This evening I'll have already done the work. As such I think 'By ...' can only be followed by verbs which describe states not actions. eg. 'By... I'll be...', 'By... I'll have done...' but not 'By... I'll do...'

If you turn the sentence round then it can be understood in one of two ways. Either as before or as the answer to the (imaginary) question 'When will you have finished the work?'.
If you are talking about something you've already begun or some kind of lenghty process then the perfect will still be the natural choice. However suppose that the task itself is not the problem but the fact, say, that you have so much else to do and might not be able to get round to it. Here, conversely, you would tend to use the simple future. eg. you might say something like 'I'll do it sometime this afternoon' which might easily become 'I'll do it (sometime) before closing-time','I'll do it by closing-time.' You will hear both future and future perfect here.

Folks,

Thank you for your answers and time!

I'll probably ask some more questions about FP tense here in the nearest future if you don't mind