Newsgroup: it.cultura.linguistica.inglese
Titolo: could vs to be able to

Regarding "could vs to be able to (in the past)", I once learned that 
one should use "could" when talking of a habit, an ability, etc..., and 
"to be able to" when talking of a particular situation.
 
Example:
"I could write very fast, but I wasn't able to keep up with the teacher 
that time."
 
Someone told me that isn't true (anymore?). What's your position on this 
matter?
 
Kiuhnm


I've never heard of this guideline, and a quick mental scan of my 
linguistic experiences does not yield any correlation with such usage.
 
Avoiding the controversy over "may" versus "can,"  the usage of these 
two terms is similar. I would venture to say it is like the difference 
between "può" and "riesce a" in that there are conventions of usage, but 
you can get away with interchanging them in most situations. Just as in 
the Italian example, the exception is for the idea of permission, where 
"can" is more appropriate than "able to" (still avoiding the may/can issue).
 
In the example you offered, the construction is actually rather (we 
should have a term for "not as a native speaker would typically say") 
cruddy. (OK, I invented my own term.) Because an ability like writing 
doesn't come and go, it would be more common to say "I can  write" in 
the place of "I could write." In fact, the way that sentence is 
constructed, "I could write" implies that you exhibited your ability 
during the period of time of that specific situation rather than having 
a habitual ability. Ironically, it sounds better to say "I was able to 
write very fast, but I couldn't keep up..." although that clearly 
implies a particular situation for the writing, too (and thus misses the 
point of your example).
 
I was able to jump tall buildings, in a single bound.
I could jump tall buildings, in a single bound.
 
Here are two arbitrary examples that bubbled up in my mind for 
comparison. Both are acceptable. The differences in connotation are 
slight, but the habitual nature is apparent in both. So, I'd have to 
conclude, after this short investigation, that the guideline is cruddy.
 

Ti riporto quello che scrive Martin Hewings nella seconda edizione di 
"Advanced Grammar in Use". Tieni conto che si tratta di inglese britannico.
 
" We sometimes use 'be able to' instead of 'can' and 'could' to talk 
about ability. However, we avoid 'be able to'
 
- when we talk about something that is happening as we speak
i.e. Watch me, Mum, I can stand on one leg (not... I'm able to stand on 
one leg)
 
- before passives
i.e. CDs can now be copied easily (rather than CDs are now able to be 
copied...)
 
- when the meaning is 'know how to'
i.e. Can you cook? (rather than 'are you able to cook')
 
If we talk about a single achievement, rather than a general ability in 
the past, we usually use able to rather than could. Compare:
 
- Sue could play the flute quite well (or... was able to; a general ability)
 
- She swam strongly and was able to cross the river easily, even though 
it was swollen by the heavy rain (not She swam strongly and could 
cross...; a specific achievement)
 
However, could is usually more natural
 
- in negative sentences
i.e. I tried to get up but I couldn't move (rather than I wasn't able to 
move)
 
- with verbs of the senses (feel, hear, see, smell, taste) and the verbs 
of thinking (believe, decide, remember, understand)
i.e. I could remember the crash, but nothing after that (rather than I 
was able to remember the crash...)
 
- after the phrases the only thing/place/time, and after 'all' when it 
means 'the only thing'
i.e. All we could see were his feet (rather than All we were able to...)
 
- to suggest that something almost didn't happen, particularly with 
almost, hardly, just nearly
i.e. I could nearly touch the ceiling (rather that I was nearly able to 
touch the ceiling)"


 touch the ceiling)"
 
All these examples are overdoing it. You can say either.

 some of the differentiations are so slight as to be considered invalid.
[...]
 
Do your remarks apply to BE, AE or both?
 
Kiuhnm

 Do your remarks apply to BE, AE or both?
 
I can only speak authoritatively on American English. Sorry, I initially 
had a mental note in mind when writing that post to make that 
distinction and it got lost in the details of writing the post. All of 
the author's comments may be perfectly correct for British English. My 
experience with British English is not comprehensive enough for me to 
know. Even so, I thought that the points made in the posted passage were 
on the whole, very good, and applied to American English as well.


Ok, thanks.
 
Kiuhnm

 "Advanced Grammar in Use". Tieni conto che si tratta di inglese britannico.
[...]
 
Thanks for taking the time to report all that!
 
Kiuhnm

 cruddy. (OK, I invented my own term.)
 
And if I say
"I could still write very fast back then, but I wasn't able to keep up 
with the teacher that day."
?
 
Kiuhnm

 with the teacher that day."
 
That is a more familiar phrasing, but the meaning is different. It 
implies that you had the ability in the past but you no longer have the 
ability. If you had the ability in the past and you still have the 
ability, you should say "I can write very fast."