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I am a new member! I am preparing for GRE analytic writing test. I do not know which word is used more often.

Thank u in advance for your kind attention.
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Both are OK for present or past ability:

I can / could open that can of worms.
I am / was able to open that can of worms
.

There is no perfect or future for can, however, so you need be able to:

(X) I will / have can catch that can of corn.
I will be / have been able to catch that can of corn
.

Can gives 1.42 billion google pages; able to gives 245 million, so they are both quite popular forms.
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In most everyday use of English, "can" is used more often than "be able to".

In addition to what Mr. Micawber has already pointed out, note that "could" cannot be used to signal success in the past.

I ran fast and was able to catch the bus. [Correct.]
I ran fast and could catch the bus. [Not correct.]

"could not" can signal failure, however.

I ran fast but was unable to catch the bus.
I ran fast but could not catch the bus.
[Both correct.]

CJ
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Comments  
CalifJimIn most everyday use of English, "can" is used more often than "be able to".

In addition to what Mr. Micawber has already pointed out, note that "could" cannot be used to signal success in the past.

"could not" can signal failure, however.

I ran fast but was unable to catch the bus.
I ran fast but could not catch the bus.
[Both correct.]

CJ

What 's the different the following tow sentences:
I ran fast and was able to catch the bus. [Correct.]
I ran fast and could catch the bus. [Not correct.]
Students: We have free audio pronunciation exercises.