Is it OK to say: 'I haven't could do it'? What I mean is that I've
been trying to do something, but actually I've not done it because
I cannot. So, how can I say this?
Thanks
for your attention, Roger. I hope I'm making myself clear enough.
Perfectly
clear, Diego. The answer is that we can't combine this tense and
this modal in this way. We must say either:
'I
couldn't do it' or 'I haven't been able to do it'.
The
difference in usage is that if we say: 'I couldn't do it',
we are thinking about a particular action or actions that were completed
in the past, e.g.
'I couldn't repair the car by myself, so
I asked a mechanic to help me.'
OR: 'I wasn't able to repair the car by myself, so I
asked a mechanic to help me.'
OR: 'I was unable to repair the car by myself, so I
asked a mechanic to help me.'
However,
if we say: 'I haven't been able to do it', we are thinking
of a period of time for the activity which extends right up to the
present, e.g:
'I've worked on it every day this week, but I still haven't
been able to complete the report.'
'They've been unable to visit him since he was admitted
to hospital.'
'Have you been able to find out anything about
her?'
This is the sort of context that you are referring to, Diego, in
the example you quote. Can has no perfect form, so we have
to use has/have been able to.
Note that we can form the negative with not able or unable.
Similarly,
can has no future form either, so we must also use be able
to + infinitive when we want to refer to the future. Study the
following examples:
'I have a very poor sense of balance, so I don't think I shall
ever be able to ride a horse.'
'He is badly injured, that's true, but I'm sure he'll be
able to walk again by the summer.'
'If the snow continues to fall, we'll be unable to leave
the house.'
Note
also that we cannot combine can with another modal verb, so
if we want to use may, might or should and combine
possibility or probability with ability, we have
to use be able to and not can or could. Study
the following:
'The doctor might be able to see you this afternoon.'
'This store is closing, but we may be able to offer
the sales staff a job in another branch.'
'I should be able to fix the upstairs toilet with the
tools in your toolbox.'
In the first two examples above, there is not much difference in
terms of possibility between may and might. They could
be used interchangeably without affecting the meaning. In the final
example above, it is likely or probable that the toilet will be
fixed.
Finally,
we normally use can or could in preference to be
able to:
in the sense of know how to
with verbs of the senses such as hear, see, smell,
feel, taste
with verbs of thinking, e.g. decide, remember,
understand, believe.
Study
the following:
'Can you speak Japanese?'
'Can you see what it says on the departures board?'
'I can't see a thing without my glasses.'
'I couldn't taste the garlic in the mayonnaise, although
my wife could.'
'I can't remember when I last saw Joan.'
'I can't believe you're going to marry him.'
'They couldn't decide whether to buy a red or a blue car.'
