[Grammar] speak clearer or more clearly

[Oceanlike]

Of the two speakers, Jay speaks clearer OR more clearly?

I thought both are acceptable, but there seems to be a difference for which I can't explain.

thank you for teaching me! :-D

 

[Raymott]

Both are acceptable. You need an adverb to modify 'speak'; 'more clearly' is obviously an adverb, and 'clearer' can be too.
Similarly: "run faster", "jump higher" etc.
Sometimes there's a version that sounds better. "Run more quickly" and "Jump more highly" aren't as natural as the terms above.