Bob,
   I see both 1a) and 1b) as ungrammatical, though I'm sure that was just
a typing mistake on your part. "Want", of course, requires the -s in
the usual spots. It definitely carries tense.>
    Modal notions can combine with each other.  (Can be able to.  Must be
able to.)  We can say "Bob may be able to," but not "Bob be able to." 
These paraphrastic forms seem to have evolved to combine modal notions
and get around the rule that finite only occurs once (and first) in a
verb phrase. In other words, it allows us to combine possibility with
ability in the same verb phrase. Perhaps "be able to" is a way to be
clear that the words are acting in a subsidiary way, not competing
with the opening auxiliary for finite status. But if you think of the
finite as taking on a certain role within the verb phrase, then double
modals can be thought of as doing that together.  It's also possible
("Bob is able to") to give both tense (in this case present) and
modality (statement of ability) in the same verb phrase.  I don't know
of a case in which tense occurs more than once, though aspect
certainly fine-tunes that. We don't say "Bob did broke my window," not
so much because it is against the rules but because we have no meaning
category for double-past. Nothing is added. But "Bob was able to"
allows us to say this is a statement about ability (a modal notion)
true for past time. That doesn't necessarily mean that tense and
modality are ultimately the same thing. It just means that we have
found good reasons to combine them in productive ways.
    We need tense or modality.  We can also have double modals or tense
plus modal.  We can't have double tense.  These all make sense to me
as observations about the intersection between form and function.
    If I say "Bob should be able to answer your question" or "Bob shall be
able to answer your question", I have not changed tense in the usual
sense of the word, though thinking of these as tensed would lead us to
believe that one is past and the other present. If I concentrate on
the generating rules as you explain them, I might give the misleading
notion that I am choosing between time references rather than choosing
between attitudes. If I am choosing between these as a writer, I am
choosing between two statements of present time attitude about
something that hasn't happened yet. One is a statement about
obligation or responsibility (since Bob is store manager, for example,
he should be able to interpret store policy), and the other is a
statement about certainty (I am certain that he can do it.)  All I'm
saying is that the question about whether or not we should CLASSIFY
"should" as past tense and "shall" as present (or future, as the old
grammars used to and may still do) is less important than paying
attention to the kind of meaning conveyed. Modals sometimes seem to
act as though they carry tense and sometimes act as if they don't.  If
we argue for one or the other, we may actually obscure the issue.
   I have many ESL students and can appreciate the need for explaining
formal rules that most native speakers never consider.  I have found a
functional perspective more effective, but that may be because that's
what matters to me. I know from some of your writing that "pragmatics"
is so important, not just to ESL students, but developing native
writers as well. If they say "must," as in "You must give me an A,"
they are expressing an attitude and may be irritating a teacher as a
result. Whether that's past tense seems much less important. It won't
tell them why their teacher got suddenly angry. They may have meant "I
deeply desire an A;" it's not at all a mistake in tense.

Craig

 Craig,
>
> My original post was a response to Jed's question about whether modals
> have "inherent tense," or whatever you want to label it, already in
> them.  (I am less interested in name for this property.)
>
> I gave a rather mundane example why some people want to make that claim.
>
> 1a) *Bob wants to can drink beer.
>   b) Bob want to be able to drink beer.
>
> If modals are just like any other verbs that have a bare form, then
> explaining 1(a) requires a very special explanation, especially given
> the fact that 1(b) is perfectly grammatical.
>
> Of course, we need to have a way of talking about the meanings of
> modals.
>
>> Certainly, the more important considerations for a public grammar >
> are how the modals add a meaning additional to whatever they
>  > may or may not convey
>> of tense.
>
> First, Jed's question was NOT about meaning.
>
> Second, my initial interest in grammar comes from ESL, and from that
> perspective, I need a way to understand non-standard constructions like
> (2) and (3a).
>
> 2)  *Bob cans drink beer.
>
> 3a)  *Bob does not can drink beer.   But,
>  b)  Bob is not able to drink beer.
>
> Examples (2) and (3a) can be accounted for by a representation of the
> first verb-expansion rule Martha presented.  This is another reason why
> I don't think it is the most insightful to describe modals.
>
> The "most important concern" you identify above is insufficient for
> me in trying to understand the non-standard forms in (2) and (3a).
>
> Perhaps, some appeal to the additional meaning modals provide can
> explain the facts of 2 and 3, but I don't know what that appeal is.
> Perhaps, I am missing something about meaning that can explain the
> formal properties of modals.  What am I missing?
>
> Bob Yates
> Central Missouri State University
>
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