Can I use these interchangeably?

I can do something now.

If I say;
I couldn't do it before.
I've never been able to do it before

Question

Can I use these interchangeably?

I can do something now.

If I say;
I couldn't do it before.
I've never been able to do it before

Answer

Both options are fine but the original isn’t.

It’s clearer to say:
Now, I can do something. (Starting with and emphasizing ‘Now’ suggests ‘now and not previously’ more clearly than putting it at the end.)

Answer

Or you can say ‘I couldn’t have done it before’

Answer

They mean the same thing, but the second has a little bit more emphasis in my opinion, as if it's amazing that you can now do it.

Answer

Both your examples are okay Pelin.

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