The syntax of inflection(44) a I think I can go
b I thought I could go
c *I thought I can go
Although I am very much simplifying things here, we can see in (43) that there is some
requirement that embedded clauses have a matching tense specification to the main
clause and hence the ungrammaticality when the main clause is in the past tense and
the embedded clause is in the present. (44) demonstrates something very similar
happens with certain modals and hence that modals seem to be specified for tense (or
at least they are not themselves in complementary distribution with a tense
specification wherever in the clause that specification is made). However, what modals
are in complementary distribution with is agreement: modals do not have forms that
are dependent on the properties of the subject:
(45) a he/she/I/you/we/etc. may/will/would/can/etc.
b *he/she wills/cans/woulds/etc.
Perhaps, then, what ‘inflection’ is, is agreement and this is expressed either as a
morpheme dependent on properties of the subject, or a modal. Of course in English the
visible tense and agreement morphemes are expressed as a single form, s. But in many
languages tense and agreement are expressed as separate morphemes, as they are in
Hungarian:
(46) elmen-t-em I left
elmen-t-él you left
elmen-t-∆ he/she left
elmen-t-ünk we left
elmen-t-etek you (lot) left
elmen-t-ek they left
In this paradigm, the past tense is represented uniformly as an independent morpheme
t and the agreement morphemes differ depending on the person and number of the
subject.
The inflectional head has a very important role in determining the nature of the
following tense head. As we have seen, modals determine that tense will appear as a
null morpheme, but note that its content, i.e. past or present, can be recovered from the
modal itself, which inflects for tense. When the inflectional element is a null
agreement morpheme, the form of the tense will be partly determined by the
agreement morpheme and partly by the tense itself. So if the tense is past then it will
be realised as ed (or one of its irregular forms) no matter what the agreement is. But if
the tense is present, it will be realised as s when the agreement is third person and
singular and as a zero morpheme when the agreement is something else:
(47) a [IP - can [vP - ∆ ...]]
b [IP - ∆3.s. [vP - -s/-ed ...]]
c [IP - ∆~3.s. [vP - ∆/-ed ...]]
We have not yet mentioned the infinitival marker to. What is its status? Is it a non-
finite agreement morpheme, similar to a modal, or is it a non-finite tense morpheme