I am not one who sits idly by when someone (or someone’s writing) sounds pretentious. I tend to, well, correct. It’s my nature. (Actually, it’s probably not my nature because my grandmother, the 1920s secretary, and my mother, the genius, were always correcting us kids whenever we used incorrect words.)
Aaaaanyway, I don’t like pretention. And to me, few words sound more pretentious than “badly” when it is used, well, badly.
Let me give you an example: I feel badly about that. Really, I do.
No, actually, you feel bad about that, whatever that is.
As a rule, “bad” is an adjective that describes or modifies nouns and pronouns. They show how something was or is, provide additional information such as size, shape, and color. Example: My commute to the stadium was bad.
And “badly” is an adverb that, you guessed it, modifies verbs because most verbs are action verbs. Adverbs can be a single word or a set of words that answer how, why, when, where, to what extent, how often, or how much. For example: When I saw my hair in the mirror this morning, I realized I badly needed a trim.
There is an exception for badly, and this is where people start to sound pretentious. If you have linking verbs like be, is, and was, the form to use is bad, not badly. (See the first example.)
Some linking verbs, like smell and feel, can also be linking or action verbs. Here, you’d also use bad rather than badly.
How would that look?
Karen felt around badly because her hands were covered in grease.
The air smelled bad.