which one?

I am not sure about the difference between the two.

He was able to trace his memory back without a doubt.

or

He was capable of tracing back his memory undoubtefully.

 

neither makes much, if any sense...

first of all, how would anyone 'trace his memory back'?... what is that supposed to mean?... one either has a memory of something, or one doesn't...

and what does 'without a doubt' refer to?... that he had no doubt that his memory was accurate?... or that the narrator doesn't doubt that the character did so?...

again, 'tracing back his memory' makes no sense... and 'undoubtefully' is not a word...

 

doubtfully and undoubtfully? I thought the latter existed too.

I am trying to understand the difference in
able and capable of

He is able to discuss his motives.
and
He was capable of discussing his motives.

with a doubt/doubtfully
and
without a doubt/ undoubtfully?

 

Did you try the dictionary? Able is having the necessary power to accomplish something while capable means having the potential to accomplish something.

 

It's undoubtedly.

But why wouldn't you just say "He remembered"?

 

Ihave..
I was able to win ( means the person won)
as opposed
I was capable of winning ( means the person did not win but could have)
I undertstand now.

Thank you for the correction.
He remembered
means differently from
He was able to remember.