Photo: stocksnap · CC0
Yes, quickly is an adverb. It is the adverb form of the adjective quick, and it describes how an action happens. In the sentence she answered quickly, it modifies the verb answered. The test that settles it: if a word describes a verb rather than a noun, it is doing adverb work.
How to tell an adverb from an adjective
Ignore the ending for a moment and look at what the word attaches to. Adjectives describe nouns. Adverbs describe verbs, adjectives, other adverbs, or a whole clause.
Adverbs answer a short list of questions: how, when, where, how often, and to what degree. Quickly answers how. A second check is movability. You can write quickly, she answered or she answered quickly and the sentence survives either way, because adverbs float. An adjective cannot wander away from its noun like that.
The -ly trap
The -ly ending is a useful hint and a terrible rule. A long list of -ly words are adjectives, not adverbs. The pattern underneath it is easier to remember than the exceptions. An adjective plus -ly usually makes an adverb, so quick becomes quickly and careful becomes carefully. A noun plus -ly usually makes an adjective, so friend becomes friendly and cost becomes costly.
| Word | Part of speech | Correct use |
|---|---|---|
| quickly | Adverb | She replied quickly |
| friendly | Adjective | A friendly reply. For the adverb sense, write in a friendly way |
| lovely | Adjective | A lovely evening |
| costly | Adjective | A costly mistake |
| deadly | Adjective | A deadly error |
| silly | Adjective | A silly question |
| likely | Adjective, and an adverb in American usage | The likely outcome. He will likely arrive late |
| early | Both | An early train. She left early |
Adverbs that never take -ly at all
The reverse trap catches just as many people. Some of the most common adverbs in English carry no -ly: fast, hard, well, soon, late, straight, often, very, here, there, now, almost, again.
He runs fast is correct, and fastly is not a word. She works hard uses the adverb hard, while she hardly works uses a separate word with a different meaning, which is why hardly is not the adverb form of hard. And well is the adverb that pairs with the adjective good. The work is good. It was done well.
When quick and quickly are both acceptable
Quick also functions as what grammarians call a flat adverb, an adverb with no ending. Come quick and get here quick are standard in speech, in commands and in casual writing, and they have been part of English for centuries. In an essay, a report or a work email, quickly is the choice nobody can mark wrong.
Two places where quick is not optional. Before a noun it is the adjective and the only correct form, so a quick answer works and a quickly answer does not. After a linking verb it is also the adjective: that was quick, never that was quickly.
Where to put quickly in a sentence
| Sentence | Verdict |
|---|---|
| She quickly read the letter | Correct, adverb ahead of the main verb |
| She read the letter quickly | Correct, adverb at the end |
| Quickly, she read the letter | Correct, fronted for emphasis |
| She read quickly the letter | Awkward, do not split the verb from its object |
| She read the letter quick | Informal, fine in speech, avoid in formal writing |
Placement changes the emphasis and nothing else. Putting quickly at the front stresses the speed. Leaving it at the end stresses the action. Both are grammatical, so pick by what the sentence is trying to say.
