In the sentence "Small children certainly do need careful supervising." Is the word "do" an adverb modifying "need" or is it a helping verb to the main verb "need"?
I'm grading papers and a student classified it as an adverb and it got me wondering whether she wasn't right. She meant it as an adverb using "do" as the opposite of the adverb "not"
It's an auxiliary verb added for emphasis. Do find the section treating of auxiliary verbs here:
There is a confusion in English regarding the classification of "do", sometimes, they may be used as a full-verb or as a helping verb, but in this case, "do" acts as an auxiliary/helping verb. Here, "certainly" acts as the adverb and provides emphasis to "need".
It's a helping verb, also called an auxiliary. However, there is an argument for calling it an adverb, as well. A modifier is something that is Chomsky-adjoined to what it modifies, and the auxiliary "do", if you believe McCawley's description (in TSPE and elsewhere) is Chomsky-adjoined to the verb it "helps".
Chomsky-adjunction is a term made up by John Ross to describe the structure of English participles which was proposed by Chomsky in Aspects of the Theory of Syntax. It means that the thing adjoined and what it is adjoined to, make a new constituent of the same category as whatever was adjoined to. The -ing form of the verb used in the English progressive looks like this:
He is [V [V eat] ing]
That is, in "He is eating", both "eat" and "eating" count as verbs. This makes "ing" a modifier of "eat", by the above account of modification.
Now, according to McCawley, auxiliaries have a similar structure, e.g.
He [V' does [V' eat fish]]
where both "eat fish" and "does eat fish" count as V' (V' are similar to VP, verb phrases). Compare the structure of a sentence with an adverb which is a V' modifier:
He [V' always [V' eats fish]]
Same structure, right? So it appears that "does" is actually an adverb, as well as being an auxiliary verb.
