Martha McGinnis: zero affixes

[Martha McGinnis]

I've been following the discussion on zero affixes, and wanted to ask a
couple of clarification questions.

First, if I understood correctly, Morris Halle (MH) observed that Tense
morphology can appear either on the main verb or on an auxiliary, depending
on the syntactic environment.  He concluded that the element realized by
Tense morphology is a syntactic node.  Andrew Carstairs-McCarthy (AC)
granted this, but contended that there need not be an independent
Vocabulary item (a morpheme-as-affix) to realize the Tense node.  How are
we to represent the fact that the Tense node is pronounced in some cases,
and isn't in others?  MH says that non-pronunciation has the same status as
a given particular pronunciation (i.e., it's a zero Vocabulary item), while
AC suggests that non-pronunciation has a different status from particular
pronunciations.

I'm curious as to how strict AC wants to be about ruling out zero
Vocabulary items.  As MH pointed out, null realization of syntactic nodes
can occur in the absence of stem changes, e.g. pro-arguments in Japanese,
say _0 wakar-u_ (understand-past) "I/you/he/she/they understood".  I'm not
sure whether AC would want to rule out zero Vocabulary items like this too.

In any case, AC's point of departure seems to be the No Blur Principle
(NBP), so maybe now is a good time to bring up something that puzzles me
about it.  The robustness of the NBP is interesting in its own right, but I
can't figure out how the child would apply it as a learning principle, even
without assuming zero affixes.  For example, suppose that a child learns
that an affix A is the default realization of a class marker on stems of
type X. This means that A can appear on several classes of X (e.g. class I,
II, III).  According to the NBP, any other realization of that class
marker, say B, will uniquely identify the class it realizes (e.g., just
class IV); this is supposed to be useful (necessary?) for acquiring the
system of class markers.

	I	II	III	IV	V	VI
	A	A	A	B	--	--

However, in addition to learning class markers A, B, etc., the child must
also learn which classes lack (overt) class markers (V, VI).  Otherwise,
s/he will use the default affix A for these classes.  Even supposing that
there are no zero affixes, why is it not a problem for the learner that the
unaffixed forms don't all belong to one class?  Why is this less of a
problem than the problem that would arise if forms with affix B didn't all
belong to one class?  Given whatever stategy the child uses to acquire the
relevant information about classes V and VI, why couldn't the same strategy
be used to acquire the relevant information about classes V and VI in the
following system, ruled out by the NBP?

	I	II	III	IV	V	VI
	A	A	A	--	B	B

Thanks for any help with these questions.

-Martha