"Follow close behind" vs "follow closely behind"?

I just came across something I'd written a while ago that contained the phrase "follows close behind", and my first thought was that it was incorrect and should be "follows closely behind", i.e. to use an adverb describing how something is following.

The Google Ngram for the two phrases seems to disagree with this instinct, though, with only slight differences between BE and AE, and the shorter phrase must've made it past my inner editor back when I first wrote it... maybe because "close" can also be used as an adverb?

So can both be used interchangeably? Is there a grammatical reason one should be considered "more correct" than the other, or is it just a case of one particular usage of a phrase having become more commonplace for some reason or other?

Solution 1:

Close is a perfectly fine adverb. It works especially well with verbs involving position or motion.

Per the OED:

In (or into) a position in which the intervening space is closed up, so that there is no interval; in immediate contact or proximity; as near as can be, very near. Esp. with stand, sit, lie, stick, cling, keep, hold, press, etc., or with vbs. of motion, as come, bring, etc.

Your instinct to use followed close behind is in keeping with these. It’s like asking somebody to stand closer to you. It just wouldn’t sound right the other way in many cases, including that one.

Solution 2:

With all due respect to @tchrist, it is routinely possible for adjectives to serve as complements for verbs, without their needing to become or be construed as adverbs. I was once challenged by a copy-editor for the sentence “If we each live solitary, therefore, some of our needs go unmet.” He or she wanted me to substitute “solitarily.” In rebuttal I invoked both the New Hampshire license-plate motto (“Live Free or Die“) and the opening line of the KJV book of the Lamentations of Jeremiah (“How doth the city sit solitary . . .”).