- Everything will be done by Tuesday.
- Everything will have been done by Tuesday.
What is the difference (semantic, grammatical), if any, between the two?
My question is different from this one because it features a different preposition, i.e. 'by' rather than 'at'.
Best Answer
The difference between "will have been done" and "will be done" is the same as the difference between "will have done" and "will do". The difference is active versus passive.
1) The work will have been done by Tuesday (by John): Passive
The active form would be: John will have done the work by Monday.
2) The work will be done by Monday (by John): Passive
The active form: John will do the work by Monday.
The first (will have been done) is an example of a future perfect tense. It is used to "to describe an event that is expected or planned to happen before a time of reference in the future" (Wikipedia)
The second is the "future" using will in a passive construction. It is used for predictions, statements of fact and intentions. Modern linguistics calls this a modal auxiliary. Here's a pretty good overview of its use: What's will?
In order to explain these passive constructions, one has to introduce an agent who need not be explicitly given when writing or saying these sentences.