Student or Learner
I've difficulty in understanding the difference between the future and the future perfect tenses when using such time expressions as 'for' as in:
1- Before you come back home, I will have been doing my homework for two hours.
2- Before you come back home, I will do my homework for two hours.
3- When you come back home, I will have been doing my homework for two hours.
4- When you come back home, I will do my homework for two hours.
Here's my try:
Sentences 1 and 2 are OK but I cannot see the difference in meaning between the two.
Sentence 3 is OK.
Sentence 4 sounds wrong but I don't know why.
#1 is not natural.
#2 is OK.
#3 is fine.
#4 is not wrong but it has a different meaning to #3. #3 means that when you arrive home I will be doing my homework and I will have started doing it two hours before you arrived. #4 means that I will start doing my homework when you arrive and I will spend two hours doing it.
"Invading armies have no rights." Noam Chomsky