roadrunner1896 asked me a really difficult question that I felt needed the attention of other native English speakers and writers/word geeks. This is basically the comment I left her (with some edits I've been doing more research/thinking):

Can you tell me the difference between "fast" and "quick"?

I don't think there is much of a difference between "fast" and "quick" except for usage. Like you would say: "He completed the course in a fast time," but not a "quick time" (at least I wouldn't say that). Or you'd say, "He completed the course quickly," but not "fastly" (because "fastly" isn't a word, though "fast" is an adverb).

Let's go to definitions:

fast moving or able to move, operate, function, or take effect quickly; quick; swift; rapid

quick done, proceeding, or occurring with promptness or rapidity, as an action, process

Pretty much the same thing. But when you get into idioms (and these are just a few examples):

fast characterized by unrestrained conduct or lack of moral conventions, esp. in sexual relations; wanton; loose
ex. Vala was fast with how she immediately progressed to undressing Daniel.
fast firm in adherence; loyal; devoted
ex. Harry and Ron were fast friends which is why Ron always wanted to come back.

quick easily provoked or excited
ex. Touch Daniel's artifacts and you'll find out that he can be quick tempered.
quick prompt to understand, learn, etc.; of ready intelligence:
ex. Hermione is a quick student, the cleverest witch of her age.

"Fast" and "quick" aren't interchangeable in those examples or for those meanings. (Though I think some people will mistakenly use "quick" in that first example of "Vala was fast".) And before anyone points it out, "a quick student" is different from "a fast learner." "A quick student" is implying something about the student herself, whereas "a fast learner" describes the speed at which one learns.

I don't think the difference can be articulated in any these-are-the-solid-and-steadfast-rules way because the English language is so deliciously mercurial, so it's probably something you'll have to pick up more through usage (sadly). Just know that while the words are synonyms, they can't arbitrarily replace each other.


Any one else have any other thoughts on fast v. quick or how the difference can be conveyed to someone who speaks English as a second language?

All definitions from dictionary.com