Rodney Huddleston argued that grammars should only allow for “inflectional distinction” between two forms of a verb when “there is at least one lexeme with a stable contrast in realisation between those two forms” (76). However, in the verb paradigm “with six forms” that he lays out, what he calls the primary plain form and the secondary plain form are syncretic in take, hit, and want, the examples he gives (74).
If “form” means the same thing on page 74 and 76, it seems like there must be a verb whose primary and secondary plain form varies, or else Huddleston wouldn’t have made them separate forms, by his own criterion.
Is there such a verb? (Or am I confused? (Or is Huddleston confused?))
Cited: Rodney Huddleston, “The verb” in The Cambridge Grammar of the English Language (2002, Cambridge UP).
They are separate forms because although they share the same shape, they belong in distinct subclasses within the paradigm. Importantly, a distinction is necessary since the present tense plain heads finite VPs, while the plain form heads non-finite ones; hence the contrast between primary and secondary forms.
Note that the verb “be” has distinct shapes for the two forms.