can/could/be able to

[Criss]

Please, can you help me with this?

What would you say is the main difference between:

I could finish my project in time
I was able to finish my project in time

I can sing
I am able to sing

Is there any big difference, and if so, what exactly tells the difference between them? Is it the context?

Thank you so much,
Criss

 

[Mister Micawber]

No real difference, Criss. 'Was/were able to' is I think more common in the past tense than 'could'. 'Be able to', of course, can be used in tenses that 'can' and 'could' are unable to be used.