Or should that be terribly? This is something that can be confusing for native speakers, and I’ve noticed recently more and more people getting into tangles with this area of language. Which ironically, I think, is due to people having more knowledge about language than before. First of all though, what aspect of language are we talking about here?
Consider the phrase feeling good. The word to feel is a verb, and good is an adjective. You probably learned in school that adjective modify nouns, being used to describe something. But if you want to modify a verb, to describe an action, then you need an adverb. Armed with this knowledge, people look at a phrase like feeling good and think that it must be wrong, as it clearly contains a verb and an adjective. The adverb form of good is well, so shouldn’t it be feeling well?
Well, no. Feeling well is grammatically correct of course, but it has a different meaning (not feeling sick) in contrast to feeling good (being in good form generally). But the reason we can say feeling good is because to feel isn’t exactly like what we usually think of when we think of a verb. We usually say that a verb is an action word, which is largely sufficient as a description, but can be a little misleading. Strictly, when we use to feel in the context we have here, there’s not really any action involved. No-one’s doing anything. Still though, it is a verb. But it’s what could be called a sense verb, along with others such as to look, taste, smell, and sound. With all of these we can use adjectives instead of adverbs, because we’re not really referring to an action, but rather describing a state. If an offer sounds good to you, you’re describing the offer, not any sound it’s making. If you say a dish tastes nice, you’re describing the dish not anything it’s doing.
These sense verbs are part of a slightly larger grammatical group known as copular verbs or linking verbs, which don’t refer to actions, but rather join subjects and adjectives. The most common one is to be: He is nice, for example, not He is nicely.
Not only is it therefore not necessary to use adverbs with these verbs (in the above contexts), but doing so will actually usually change your meaning. Most of these verbs can also have an active, dynamic meaning, with which it is correct to use an adverb. Consider the joke which gives this post its title. (In case you’re unfamiliar with it – Tom: “My dog has no nose.” Steve: “How does he smell?” Tom: “Terrible!”). The joke is of course based on the fact that Tom mistakes Steve’s use of to smell as a dynamic verb (i.e the act of smelling), with its use as sense verb. If Tom had understood Steve and ruined the joke more than I just have, he would have answered He smells terribly, or He can’t smell: he has no nose. Didn’t you hear me?
Even though it’s grammatically correct to use adverbs with these verbs in their dynamic meaning, it’s rare that you’d ever need to do so. To use taste well, for example, one would need to say that someone tastes well, i.e. that they’re good at the act of tasting. Or to take the most common error I see with these verbs: I feel badly. It seems to be quite popular lately, but using to feel with badly means that to feel is therefore being used as an action verb, referring to the action of sensing something through touch. To feel badly would therefore mean to be incompetent in terms of physically feeling things. Which could be the case for someone with a condition in their hands, but how likely is it that you’d ever need to say that?
Still though, it’s not like saying feeling badly is the worst thing in the world. Its meaning is still clear and it’s been used by many people for quite a while (apparently to distinguish an emotional feeling, e.g. I feel badly about what I did, from a physical one, e.g. I feel bad: I’m sick. Perhaps you use it like that). But if you’ve ever felt it might be wrong to use an adjective with these verbs, hopefully now I’ve cleared things up for you. It just goes to show how a little knowledge (verbs need adverbs, not adjectives) can lead you astray, and how languages can seem to resist their own systems of logic.