I know that quickly is an adverb, but can fast function as one? I was talking with one of my friends about it and he said that you can go fast. He also said that you can't run fast. You can go quickly and you can run quickly though. What are the actual rules regarding this topic?
Fast is part of a group of adjectives that have gone all delinquent and are found slumming with adverbs as often as with their adjectival peers. Fast, good, hard.... If one is to side with tightly prescriptive grammarians, fast should never be modifying any verb other than a copula verb.
"I can run good," obviously sounds horrid. But, "I can run fast"? Who would think 'fast' didn't act as a normal adverb? The Free Dictionary allows it as an adverb. http://www.thefreedictionary.com/fast:
