Re: SURVEY: Idiomatic Expressions In Your ConLang Or ConCulture

Jim Henry wrote (re: 'I guess I better had.'):

>"I better had" wouldn't work in my 'lect either; it would
>be "I had better" or more likely "I'd better".
>[snip]
>It doesn't work with any other tense or mood of "to have"
>in English, either; *"I will have better", *"I would have
>had better", *"I have better"....  So definitely an idiom.
All true for my 'lect also, though the tense of the dependent
verb can be modified - cf. "I'd better have finished before
the boss gets back.", with future perfect meaning.

It seems to me that the construction is syntactically
parallel to modal auxiliaries - cf.:

"I should go." / "I'd better go."
"I should have gone." / "I'd better have gone."
"My father said there'd be trouble if I didn't mow the lawn,
so I guess I should." / "...so I guess I better had."

"Should" may occur, as in the last example, without (or *as*?)
a main verb, when it's stressed for focus - this can also
occur in a main clause:

"My father said I *should*, but I won't."
"My father said I better *had*, but I won't."

Is it perhaps the case that "better had" is the allo-, er,
-morph? -lex??, well, the form that "had better" takes when
it's stressed and/or acting as a main verb?

Jonathan.