I am happy the next time she comes.
The next time she comes, I am happy.
The above-mentioned sentences are clear in having the same meaning.
However, I would like to know if there's a subtle difference between these (presence of auxillary verb):
I am able to do it the next time she comes. (I think "am able" here is referring to my current ability i.e. "I can do it the next time she comes." )
The next time she comes, I am able to do it. ("Am able" is referring to the future ability I am sure that I will have; zero conditional)
future events for instance "I start my new job next Monday" and "My train leaves on Saturday" are as correct as "I'll start my new job next Monday" or "My train will leave on Saturday", aren't they? I got them from a Cambridge grammar book.
'Can' (but normally not 'be able to') is an exception to this general rule, since we may refer by means of it to an expected future ability to accomplish some particular task at a certain future time, but normally only where this constitutes an undertaking/promise of some kind, e.g.
I can see you briefly next Thursday morning.
*By the end of the course, I can speak French fluently.
(-->...I'll be able to...)
 I can do it (the) next time she comes.
[1a] (The) next time she comes, I can do it.
which would, in fact, be identical, both structurally and semantically, differing only in the obvious, minor respect of clause-ordering, with  being slightly the more natural choice.
'Can' here would naturally be understood in either as having a future meaning (please refer also to my comments on this point in post #6).
Note, incidentally, that the term 'conditional' applies only to sentences containing, or implying, 'if'. It is therefore not applicable here.
Yes - If you change "I am" to "I can" then things change. The point is that "I am" cannot be used when referring to the future.
As I have already indicated. The rephrasing with 'can' was offered simply as a correct example of the type of sentence that the questioner was apparently endeavouring to make (i.e. one referring to future ability).
I'm not sure if I understand your comment on the conditional being restricted to "if" statements -
I was referring to the application of the term conditional to a sentence-type. Conditional sentences are those consisting (typically) of a main clause modified by an adverbial if-clause. They do not necessarily contain forms of the conditional mood (i.e. [would V] etc.).
"They could have went to the moon or to Mars."
I believe you mean 'could have gone...'.
ENGLISH PAGE - Conditional Tutorial ?
What about talking about the general future (changing "next time" to "if"):
I can(am able to) do it if she comes.
If she comes, I can(am able to) do it.
'Am able to' has a similar meaning to 'can' and in many cases they can be used interchangeably, but that does not mean that they have to follow exactly the same behaviour grammatically. Can is a modal and be is not, just as must and have to can have similar meanings, but they don't always behave exactly the same way. A synonym of an irregular verb doesn't have to be irregular and a synonym (or near synonym) of a modal isn't a modal.
There are contexts where I think 'I am able to do it tomorrow' might work- if you trying to make an appointment and I have my diary open in front of me and see that I am free tomorrow, then I don't think it would be an error to use it because I could look at it as a current ability. However, this is stretching a point and I would be far more likely to say 'I can do it tomorrow'. Things like 'the next time she comes, I am able to do it' might be heard in speech, but it's pug ugly.
Isn't I can = I am able?
Not in every way, no
Last edited by Tdol; 28-May-2010 at 18:15.