Which one of these adjectives is correct? I can see that both of them are being used, I'm just not sure which one is grammatically correct.
Are there any general rules to follow as to the use of one against the use of the other?
The basic rules of forming comparatives:
One-syllable words take "er":
Multisyllable words take "more":
Two-syllable words ending in consonant + "y" take "ier":
Both "more clear" and "clearer" are acceptable:
Your answer is more clear than mine.
Your answer is clearer than mine.
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."