Fast vs. Quickly – Which is Correct?
Both fast and quickly are correct, but they do not always fit the same sentence. Fast can be an adjective or adverb, often describing speed or movement, while quickly is an adverb meaning “at a rapid rate.” Choose fast for concise, everyday phrasing and quickly when modifying an action explicitly.
Fast or Quickly – Which is Correct?
Fast and quickly are both correct American English words, but they serve different grammatical functions. Fast can be an adjective describing a person, animal, object, or process with high speed, as in “a fast runner.” It can also be an adverb, as in “She runs fast.”
Quickly is an adverb. It describes how an action happens and usually modifies a verb, as in “She quickly finished her work.” In many contexts, either word is possible: “He drove fast” and “He drove quickly” are both grammatical. However, fast is shorter and more conversational, while quickly makes the adverbial function especially clear.
The Best Trick to Remember the Difference
Use this simple swap test: if the word describes a person or thing, choose fast; if it explains how an action happens, choose quickly. For example, “a fast train” describes the train, while “the train moved quickly” describes the movement.
Another useful clue is that fast commonly comes after a verb without an ending: “run fast,” “work fast,” and “learn fast.” Quickly usually ends in -ly, signaling that it is an adverb: “run quickly,” “work quickly,” and “learn quickly.”
| Word | Part of Speech | Meaning | Example |
|---|---|---|---|
| fast | Adjective or adverb | Moving or happening at high speed | The fast cyclist finished first. / She runs fast. |
| quickly | Adverb | At a rapid rate or without delay | He quickly answered the question. |
How to Use Fast
Fast is a flexible word that works as both an adjective and an adverb. As an adjective, it comes before a noun or after a linking verb: “a fast car” and “The car is fast.” As an adverb, it usually follows a verb and describes rapid movement or action: “The car moved fast.”
Fast is common in casual conversation, journalism, advertising, and everyday writing. It is concise and natural, although quickly may sound more precise in formal writing when the word clearly needs to modify an action.
Example 1: The fast train connects the two cities in less than an hour.
Example 2: Please walk fast if you do not want to miss the bus.
Example 3: The company is growing fast because demand has increased.
What are the different forms of fast?
When fast is used as an adjective describing speed, its comparative form is faster and its superlative form is fastest. For example, “This route is faster than the old one” and “That was the fastest lap of the race.” The adverb also uses faster and fastest: “She ran faster today” and “He finished fastest.”
Fast can also have meanings unrelated to speed. As a verb, fast means to refrain from eating, with the forms fasted and fasting. As an adjective, it can mean firmly fixed, loyal, or not easily moved, as in “a fast friendship” or “hold fast.”
Etymology of the word fast
Fast comes from Old English fæst, meaning firm, secure, or fixed. Over time, the idea of being firmly established developed into the meaning of moving firmly or strongly, and eventually into the modern sense of moving at high speed. The related meaning of abstaining from food comes from the Old English verb fæstan.
How to Use Quickly
Quickly is an adverb formed from the adjective quick and the suffix -ly. It describes the manner, timing, or speed of an action. It can appear before a main verb, after a verb, or at the beginning or end of a sentence: “She quickly left,” “She left quickly,” and “Quickly, she left the room.”
Quickly is useful in formal, academic, professional, and everyday writing. Compared with fast, it can sound slightly more explicit or polished because its -ly ending clearly identifies it as an adverb.
Example 1: The technician quickly identified the problem.
Example 2: Please reply quickly so we can finalize the schedule.
Example 3: The children quickly became interested in the science experiment.
What are the different forms of quickly?
Quickly is an adverb and does not normally change form for tense, number, or person. The related adjective is quick, while the related noun is quickness. The comparative and superlative forms are generally expressed with more quickly and most quickly, although quicker and quickest are sometimes used informally as adverbs.
Etymology of the word quickly
Quickly comes from the adjective quick, which derives from Old English cwic, meaning alive or living. In Middle English, quick developed associations with liveliness, activity, and speed. The adverb quickly came from adding the Middle English adverbial ending that later became modern -ly.
Related Concepts
Understanding parts of speech and adverb placement makes the difference between fast and quickly easier to recognize.
- Adjectives: Adjectives describe nouns or pronouns. In “a fast runner,” fast describes the noun runner.
- Adverbs: Adverbs modify verbs, adjectives, or other adverbs. In “She ran quickly,” quickly explains how she ran.
- Irregular adverbs: Some adverbs do not end in -ly. Fast is one of them, so “He drives fast” is correct.
- Comparative adjectives and adverbs: Words such as faster and more quickly compare the speed or manner of two actions.
Examples from Media and Literature
Both words appear frequently in storytelling, reporting, advertising, and everyday dialogue. The following examples illustrate their typical use without relying on a fixed quotation.
- Sports reporting: A commentator may describe an athlete as “fast” or report that the athlete “quickly moved into first place.”
- News writing: A report may state that a wildfire “spread quickly,” emphasizing how the event developed.
- Film dialogue: An action character might tell someone to “run fast,” using a concise, conversational adverb.
- Children’s literature: A story may introduce “a fast rabbit” and then explain that the rabbit “quickly escaped.”
- Advertising: A delivery service may promise “fast shipping,” while its website may say that orders are “processed quickly.”
Practice Exercises
Choose the correct word to complete each sentence.
- The cheetah is one of the ______ animals on Earth. (fast / quickly)
- Please complete the form ______. (fast / quickly)
- She can type very ______. (fast / quickly)
- The new software processes large files more ______. (fast / quickly)
- That was the ______ route to the airport. (fast / quickly)
Answer Key
- fast — It is an adjective describing the animals.
- quickly — It is an adverb describing how the form should be completed.
- fast — Fast can function as an adverb after a verb.
- quickly — It describes how the software processes files.
- fast — The superlative adjective describes the route.
Fast Synonyms
| Synonym | Definition |
|---|---|
| Rapid | Moving or happening at a high speed; often more formal than fast. |
| Swift | Moving with great speed, often suggesting smoothness or efficiency. |
| Speedy | Fast or completed in a short time; informal in tone. |
| Brisk | Energetic and quick, especially when describing walking or activity. |
Quickly Synonyms
| Synonym | Definition |
|---|---|
| Rapidly | At a fast rate or speed; suitable for formal writing. |
| Swiftly | With speed and efficiency, often in a polished or literary style. |
| Promptly | Without delay, especially when referring to a response or action. |
| Hastily | Quickly and often with insufficient care or consideration. |
Frequently Asked Questions
Question 1: Is “do it fast” grammatically correct?
Yes. Fast can function as an adverb, so “Do it fast” is grammatically correct and common in informal conversation. “Do it quickly” is also correct and may sound more polished or explicit.
Question 2: Is “fast” or “quickly” better in formal writing?
Neither word is always better. Use fast when describing speed concisely, particularly before a noun or after certain verbs. Use quickly when you want a clearly marked adverb or a more formal tone.
Question 3: Can “fast” describe an action?
Yes. In “The horse runs fast,” fast is an adverb describing the action of running. It is an irregular adverb because it does not end in -ly.
Conclusion
Fast and quickly are both correct, but fast can be an adjective or an adverb, whereas quickly is an adverb. Use fast for concise descriptions of speed and quickly when emphasizing how an action occurs. Pro Tip: Choosing the word that best fits the sentence makes your professional writing sound more precise and polished.
