zero-marked verbs

[jaw300t]

Colleagues,
For the past couple of years I've been following a certain unmarked verb form
in Kuche (also known as Rukuba, listed in the Ethnologue as Che), a language
of Nigeria.  I had the feeling it ought to be the simple present tense.  In
elicitation sessions, informants never gave this form in response to an
English simple present tense sentence, although in conversation it would often
be used that way.  In discourse, it is the most common verb form of all,
seldom used as a simple present tense verb; there are about 20 different verb
markings that can be used, but the unmarked form is used in many texts more
than all the others combined.

Fleischman's "Tense & Narrativity" and Bybee, Perkins, & Pagliuca's "The
Evolution of Grammar" opened up some possible explanations.  But what really
crystallized it for me was something in an earlier article by Bybee ("The
Grammaticization of Zero" in a volume edited by Pagliuca).  She says, "When a
grammaticizing OVERT morpheme becomes obligatory, it may happen that other
meanings within the same functional domain, which previously had no
grammatical expression, come to be expressed by a meaningful zero."

It seems Kuche is at a point in its history where overt tense/aspect morphemes
are NOT obligatory.  What happens to the unmarked form, then, is that it has
NO SPECIFIC meaning--it means just about anything, depending on context.
Overt tense/aspect markers are used at the beginning of a discourse, and those
tense/aspect interpretations hold over long stretches of discourse.  This is
much like Longacre's "consecutive" tense, except that this unmarked form is
remarkably flexible.  It can even be used after an imperative with imperative
force--a second imperative verb would be even less marked, because the
unmarked form IS marked for subject agreement, while the imperative is not.

I suppose Kuche is not unique among non-written languages in having a
flexible, relatively unmarked form.  I don't see them mentioned in Bybee,
Perkins, & Pagliuca.  Then, again, I suppose it's a matter of degree--in some
languages, the interpretation assigned to a zero-marked form might be a little
flexible, and in other languages, the interpretation of such a form might be
quite specific.

What is it in a language community that causes OVERT TAM marking to become
obligatory?  Is it the transition to written literature?  Fleischman says
(quoting somebody else, if I remember correctly), that "The meaning of written
literature is in the text; the meaning of oral literature is in the context.)

Janet Wilson