Could have done or were able

Velimir

We could have done it either way.

2.  It is possible that we did it either way.  (I don't remember which way we did it.) 

3.  We had the skill (ability, talent) to do it either way. (Nothing said about whether we actually did it.)

Velimir

We were able to do it either way .

2.  We succeeded in doing it in both ways. 

_____

Obviously, there is some overlap.   

CJ 

Velimir

Thank you very much for your answers Thomas Thompion and CalifJim,

Those ambiguities are exactly the problem for me, specially in regard to expressing  "past ability". In many situations I can't easily decide what "could" or "could have" really mean : "able", "possible" or "optional".  I'm not really sure of the distinction you are making here, Velimir.  Clearly it wouldn't be an option if it were not possible, and it wouldn't be possible for you if you were not able to do it.  However, I'm not sure that there is much of a difference in use:  let's return to the case of the fire and the door -

The fire was raging
1.  but I could open the door - i.e. I did actually open the door.  This is the case where some people will tell you it's wrong to say I was able to open the door (which might certainly indicate a general ability, though that's not we're talking about here).
2. and I could have opened the door - i.e. I didn't actually open the door; I got out by some other means or I was incinerated, and am telling the story to some heavenly or hellish companions.

I most often understand "could have + verb" as "quite possible action which didn't happen" but sometimes also as denoting "ability to do".  "Was able to" many times sounds awkward to me as it would be for example in the slightly different sentence from the one Thomas gave in his post :

The fire was raging but luckily I was able to open the door - this is the one many people would tell you is wrong.  For me it would be a very odd form of words to use and implies that you did open the door.  If you actually didn't open the the door you'd need some sort of concessionary expression at the start of the clause - though I could have opened the door, I climbed through the window.


I tend to use "could" instead of "was able" in similar situations but in Michael Swan's "Practical English Usage" it's clearly stated : We do not normally use "could" to say that somebody managed to do something on one ocassion, instead we use "was able" , "managed" , "succeeded" etc." . I agree with him about 'managed', 'succeeded', etc. but I think he is heterodox on the point about not using 'could' on such occasions (note spelling). In the next passage Swan gives exceptions to this and gives list of verbs which can be used with "could" to denote ability to do something.  Those verbs are : "see" , "taste" ,"understand", "feel" , "hear" "smell" and "guess" . This seems fair enough. He also says that "..we use "could" for "general ability" to say that somebody could do something at any time,whenever he/she wanted. In negative clauses to denote inability i.e "couldn't"+ verb, it can be freely used in this sense.  Obviously I agree with this; it's what I said in my post above.

 Would you please check the three varieties of the following sentence so I can reduce a bit a confusion about this point.  For example,not having a can opener, I've just opened a can of tuna fish with a knife and I'm kind of joking with my friend :


I could have opened it with a fork as well. - Let's put aside the problem with as well, which suggests you might have used both.  This is fine: you might have used a fork but you did actually use a knife.

or

I could open it with a fork as well. - Not for me.  This suggests you haven't opened it yet and are considering possible strategies.

or

I was able to open it with a fork as well. - Nor this one.  This is a funny way of saying you did actually open it with a fork as well as a knife.  I wouldn't know what you are talking about.

I know you have had other answers to these questions and I may not be taking what other people have said into account here, and I may be making points already made without acknowledgement.  This isn't out of bad manners, or a lack of interest in what other people have said, but just that I'm new here and haven't yet learnt how to consult the thread while using my editor.  There probably is an easy way but I'm not going to risk it, for fear of losing what I've written. 

Thomas Tompion

p.s. I hope you'll forgive me for putting comments into your text.  I thought it the easiest way of replying.

Thank you very much for your help