"More clear" vs "Clearer": when to use "more" instead of "-er"?

The basic rules of forming comparatives:

One-syllable words take "er":

• clear -> clearer
• sweet -> sweeter

Multisyllable words take "more":

• incredible -> more incredible (not "incredibler")
• horrible -> more horrible (not "horribler")

Two-syllable words ending in consonant + "y" take "ier":

• happy -> happier
• pretty -> prettier

Both "more clear" and "clearer" are acceptable:

Your answer is more clear than mine.

Your answer is clearer than mine.

Frequency of use: clearer than is twice as common as more clear than, although both are common.

Both are grammatically correct. ("More clearer", however, would be wrong.)

The question really ought to be whether to say "clearer" or "more clearly." That's the confusing one. I believe it is correct to say that "I see more clearly now that I've wiped my windshield", and incorrect to say "I see clearer now that I've wiped my windshield."

The problem is that comparative adverbs like "better" make you think that "clearer" is the correct comparative adverbial form. But you don't "see clear," you "see clearly."