My biggest grammar peeve is using adjectives when you need an adverb (and vice versa). Example: "I feel badly" instead of "I feel bad." -- Tiffany
Sorry, Tiffany. Actually, “I feel bad” is the correct choice. Here’s why: Most of us were taught that adverbs modify verbs. But an alarmingly small proportion of us ever learned about copular or linking verbs, which can turn our basic understanding of adverbs on its head. So we have no choice to assume that "I feel badly" is the correct choice over "I feel bad."
Unfortunately, that just isn't so.
To understand the principle of copular or linking verbs, ask yourself: Why do you say "I am happy" instead of "I am happily"? It's because "happy" is really describing the subject "I" and not the action of the verb, right? That's a good place to begin understanding copular verbs, but it doesn't end there.
The most common copular verb is "to be." Many others also refer to states of being or to senses: "seem," "appear," "act," "become," "look," "remain," "get," "grow," "smell," "feel," "taste."
And the rule we've been accidentally yet so conveniently kept in the dark about is this: Copular verbs take adjectives as their complements. Not adverbs.
The dog appears hungry (not hungrily).
The suspect acts guilty (not guiltily).
The haggis smells bad (not badly).
John became angry (not angrily).
Of course, most copular verbs aren't exclusively copular. The word "appears" in the above example describes the dog, so it's copular and takes an adjective. But if you wanted to say that the dog "appears suddenly," it's not copular because you're describing an action -- appearing. Another example, "feel" is copular when describing a mental state, but when you're describing the action of touching and feeling, it's not copular. That's why "I feel badly" isn't always wrong.