‘Fast’ vs. ‘fastly’ vs. ‘quickly’ in English

by Jakub Marian
Tip: Did you know that “iron” is pronounced as “I earn”, not as “I Ron”? Learn more about the most common pronunci­ation mistakes in English (PDF version).

Many English learners use the word “fastly” as an adverbial form of “fast”, which seems quite logical because this is the way adverbs are usually formed. For example, if something is slow, you say that it “moves slowly”, which is completely correct. Nevertheless, languages develop in a way that is not always logical and, the situation of “fast” vs. “fastly” falls exactly into this category. The fact is that there is no such word as “fastly”. “Fast” is already both an adjective and an adverb, for example:

The athlete runs really fast. (correct)
The athlete runs really fastly. (wrong)

It doesn’t matter whether “fast” refers to a movement or to the rate at which something is being done; it’s always just “fast”:

He can’t write fast enough. (correct, informal)
He can’t write fastly enough. (wrong)

The word “quickly”, used as an adverb, is synonymous to “fast”, but usually refers to the time an action takes rather than to the speed of movement. For example, you can say

Come here, quickly!

which means that you want the other person to come soon; you don’t really care how fast he or she is moving. Nevertheless, “quickly” can also refer to the actual speed (as in “he runs quickly”), but such usage is much less common. However, there is one situation in which it is obligatory to use “quickly” (or “swiftly” or a related adverb ending with “-ly”)—if an adverb precedes the verb it modifies:

He quickly ran out of the building. (correct)
He fast ran out of the building. (wrong)
He fastly ran out of the building. (wrong)

By the way, are you not a native English speaker? Then you should check out the list of over 500 commonly mispronounced words I have compiled in the form of a book. There's also a downloadable PDF version.

Do you have a remark? (Currently 0 Comments)
Join the weekly educational digest:
and receive 2 free ebooks.
Title image by: G. H. Grimshaw (Public Domain)  •  Privacy policy and Amazon Afiliate links