[Grammar] since + present simple?

[tyrp]

Hello, everybody,
Could you possibly help me with the use of tenses in sentences like:
E.g. I've been working at night as a janitor since I AM / HAVE BEEN a student.
Are both options possible? In the example in the book, we had: Alice has been studying French since her sister has been away on training in Paris. Will it be a mistake to use simple present in both sentences above? If I come to think of it, the actions cover the same time-period, so why not use the same tenses? Do simple present and present perfect differ in meaning here? Thank you so much for your kind help!

 

[teechar]

I've been working at night as a janitor since I [STRIKE]AM / HAVE BEEN[/STRIKE] was a student.

Alice has been studying French since her sister [STRIKE]has been[/STRIKE] went away on training in Paris.

When used in a present perfect sentence, "since" marks a past point in time.

 

[tyrp]

Thank you very much, dear teechar, but could you possibly consider the following information and clear it all up for me.
Is it not a state meant by the verb in my examples above? The state of being a student or being away? Our book has it that if "since" shows an action, and, thus, a past point in time, then simple past is used.
E.g. Alice has been studying French since her sister went away. (The sentence encompasses two actions: Alice has been studying French, say, for 5 years. We can pinpoint the day of her sister's departure. It can be cleared up if necessary. E.g. Her sister went away in 2001).
In case the action with "since" shows a state (which has got no beginning or end, actually), the verb takes the present perfect tense as the two parts of the sentence will cover the same time-period.
E.g. Alice has been studying French since her sister has been away.(The sentence falls into two like these: Alice has been studying French, say, for 5 years. Her sister has been away for the same period of time, i.e. Her sister has been away for 5 years. We can't use the verb combination "to be away" with the exact date (implied by simple past here) and mark the beginning of the other action with it. So simple past is impossible if the verb "to be away" is preserved and not changed for "to go away". The same situation with action/state difference crops up in sentences like: I've already reached the station. = I'm at the station already. I've been at the station for 5 minutes already.) This explanation seems quite logical to me. Do you not agree with it? Is the present perfect impossible after "since", in your opinion? Thank you again for your time and help.

 

[Tarheel]

Perhaps:

Alice has been studying French since her sister left.

 

[teechar]

This explanation seems quite logical to me.

It doesn't to me.

Do you not agree with it?

No, I don't.

Is the present perfect impossible after "since", in your opinion?

Yes, it is; "since" marks a point in time.

 

[bhaisahab]

In my opinion your sentence would be more natural as: " I've been working at night as a janitor since I became a student."