The other day I received a great question from a reader of this blog. It was:
"Which is correct?
Let me explain something really quick.
Let me explain something really quickly."
And while I did answer her, I do feel like many people have the same question. Hence, this blog post.
The correct answer is:
Let me explain something really quickly.
Forget about the word "really" for a second. How would you write your sentence? The right answer is "Let me explain something to you quickly". Why? Because the adverb "quickly" is modifying the verb "explain".
Note: Adjectives modify nouns. Adverbs modify verbs, adjectives, and other adverbs.
The trick to solving whether or not to use an adjective or an adverb after seeing "really" is to remove "really". Once you do, then you'll know what kind of word you're modifying.
Take the next sentence:
"I think she's really pretty."
Remove "really" and you have "I think she's pretty". You would not write "I think she's prettily", so use the adjective "pretty", not the adverb, "prettily".
To add an interesting twist to this, the word "fast" can act as both an adjective and an adverb. So you could also write this sentence as "Let me explain something to you really fast", and you'd be correct.