"Juan has been working for three hours"

[Jon Aske]

Hi, Mark,

Interesting question.  I guess my first comment would be that I don't think
we should call this a "construction", but rather a linguistic "function",
or "meaning", which may be expressed by different constructions, even
within one language, as you point out happens in Spanish, and as happens in
English too.

The hace .. que construction in Spanish seems to be etymologically
equivalent to the English "It's been ... since/that ... ".  Its range of
applicability, however, is rather different.

You didn't mention that in the construction in (c) the time expression
following desde "from/since" must have the "hace + period of time" if the
time expression doesn't mark a point in time, but a period of time:
Juan trabaja desde hace tres horas.

The role of hace in these constructions is really interesting.  By most
tests it seems to still be a verb, not least of all because it is still
conjugated.  Not only that, the time expression, if emphatic, can be
fronted to preverbal (F1) focus position:
TRES horas hace que trabaja Juan!

And, of course, there is the Spanish llevar "carry" construction which also
instantiates this same general function/meaning:
Juan lleva tres horas trabajando
Juan lleva trabajando desde que llegó

Please do post a summary if people write directly to you.

Best, Jon

-------------------------------------------------------------
Jon Aske -- Jon.Aske at salem.mass.edu -- aske at earthlink.net
Department of Foreign Languages, Salem State College
Salem, Massachusetts 01970 - http://home.earthlink.net/~aske/
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In youth we learn; in age we understand. --Ebner-Eschenbach.