Thank you for your input! The main challenge in writing a rule for this is the fact that “more old” can be correct as well. To wit, when it’s not a comparative:
In the future, there will be more old people than today. (not: older)
Is she old and wise? – She is more old than wise. (not: older)
The challenges concerning comparative and superlative morphology are minor. There are a few pitfalls, though:
This does not hold true for clever, quiet, narrow, simple who all have an -er comparative.
This does not hold true for all bisyllables ending in -ly, e.g. surly > surlier (not more surly).
That said, you are absolutely right that the comparative and superlative rules could be much bolder than they are.
An adjective (in its positive form) that forms the comparative synthetically (-er) and not analytically cannot be preceded by “more” unless
more is at the beginning of the sentence,
- the adjective is followed (by another adjective and then) a noun unless before more, you have an article,
- the adjective is followed by than and another adjective (positive form), or
- the adjective is followed by than and a personal pronoun (nominative) and a finite form of “to be”.
More old people are moving to this quiet village every year.
She is an older lady. (not: more old)
There are more rich old people here than in any other state.
He is more old than wise.
He is more old than he is wise.
An improved comparative rule is in the works.
As for the superlative, the situation is somewhat different:
An adjective (in its positive form) that forms the superlative synthetically (-est) and not analytically can only be preceded by “most” when:
- it is followed by a noun unless it is preceded by the unless before that, there is a transitive verb.
She is the oldest.
I suppose that most old people have pensions.
She is the oldest sister.
He is the person who knows the most old people.
An improved superlative rule is in the works.