MARCH 6, 2008 | Did you do it fast or quickly?
Most native speakers *including us* will tell you that there is a slight nuance between the two. To our ears, "fast" sounds more natural when referring to physical speed, something you can see or feel. So, the old argument that "quickly" refers to time and "fast" to speed seems correct... but not always - eg. "Don't drive so fast" (referring to speed) could easily be replaced with "Don't drive so quickly", and "They got there quickly" (referring to time) could easily be replaced with "They got there fast." :)
So, as you can see, there is no strict rule on this, at least as far as American English usage is concerned. British English generally avoids using "fast" as an adverb.
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