can/will be able to

[rajeshmalladi]

1) I will be able to speak english by the time I finish this course.
I can speak english by the time I finish this course.

2) With a sudden burst of adrenaline, he was able to lift the car off the child's leg.
With a sudden burst of adrenaline, he could lift the car off the child's leg.

Please explain the differences.

Thank you,
Rajesh.

[Rusty]

1) I will be able to speak English by the time I finish this course. (Correct).
I can speak English by the time I finish this course. (This doesn't sound right. "By the time" seems to be the problem. You can say "I can speak English when it becomes necessary." I'll see if I can find some more information on this).

2) With a sudden burst of adrenaline, he was able to lift the car off the child's leg. (Correct).
With a sudden burst of adrenaline, he could lift the car off the child's leg.
(Ambiguous. "With a sudden burst of adrenaline" does not tell us whether the action was in the past or a possibility in the future).

[Rusty]

I can speak English by the time I finish this course. (This doesn't sound right. "By the time" seems to be the problem. You can say "I can speak English when it becomes necessary." I'll see if I can find some more information on this). (The reason it doesn't sound right is that it is wrong! The verb "can" cannot be used in the future tense. You have to change to "will be able." "By the time" is in the future).