I checked this and this answer, but it still unclear to me.

Let's say

This car is fast (slow, careful, lazy) Here fast/slow definitely is adjective, it describes the car.

But if we modify the sentence in this way

This car is riding slowly (carefully, lazily)

the 'slowly' is an adverb, because related to verb 'riding', correct? Then why

This car is riding fastly

sounds terribly awkward? What should be used here and why?

  • 2
    First, you probably want to replace "riding" with "driving" or simply "going". Cars don't ride, though people can certainly ride in cars. Second, the last example is awkward because fast is both the adjective and the adverb. There is no *fastly. But you could use quickly, and it would be just as acceptable as slowly (as opposed to quick, which would put off some pedants).
    – Dan Bron
    Commented Jun 14, 2016 at 21:32
  • PS: I think this question is fine here, it's well-researched and well-presented, but you might also like to check out our sister site, dedicated to helping people learn English as a foreign language: English Language Learners. It's friendly, fun, and full of great teachers.
    – Dan Bron
    Commented Jun 14, 2016 at 21:48
  • Related.
    – tchrist
    Commented Jan 28, 2023 at 16:09

1 Answer 1


To answer your question very simply, fastly is unfortunately not a word! According to the Merriam-Webster dictionary, the proper adverb is simply fast.

He ran as fast as he could.

You could of course use "quickly" instead.

You also might want to consider changing "riding" to "moving," simply because to ride is a transitive verb.

Best of luck to you! —C.T.

  • 1
    'Ride' can be used without an object. However it does mean that the car is being carried (quickly) by something else, which is probably not what is meant. Commented Jul 15, 2016 at 16:21

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