Be parallel!

When you create a compound structure in a sentence (such as a compound predicate, which we have here), you need to be careful. Both parts of the compound (both sides of the conjunction) should have the same structure. Look at the second panel in this Buckles:

He says the hair provides protection as well as holding the heat in. “Provides” is not the same verb form as “Holding,” so the two parts of the sentence aren’t parallel. Bad. Restate the sentence with “and” instead of “as well as” and the non-parallelness is easier to see. The hair provides protection and holding in the heat? Nah. It should be “provides protection as well as holds in the heat.”

You have a way around this, by the way, if you don’t like that way of saying it. Replace “as well as” with “while.” “While” turns the second phrase into an adverb, which modifies the verb without trying to be parallel to it. “Provides protection while holding in the heat.” That works!

PS—This error is not uncommon, by the way. I just ran into it in a Scientific American article:

Scientists think that its unusually low density causes impacts to indent the surface rather than excavating it.

Should be “excavate.”