Slow and slowly both relate to low speed, delayed progress, or gradual action, but the difference is not simply “adjective versus adverb.”
“We had a slow trip.”
“The train moved slowly.”
In the first sentence, slow describes the trip. In the second, slowly describes how the train moved.
However, slow can also work as an adverb or verb:
“Drive slow near the school.”
“Traffic slowed near downtown.”
The best choice depends on grammatical function, sentence position, intended meaning, and writing style. This guide explains both the safest edited form and established expressions such as go slow and take it slow.
Quick Answer
Use slow to describe a noun or a subject’s condition. Use slowly as the regular adverb for how an action happens.
- a slow driver
- The driver moved slowly.
- The internet is slow.
- The page loaded slowly.
Slow also functions as an adverb in accepted commands and expressions such as “Drive slow” and “Take it slow.” When describing an action in formal writing, slowly is usually the safest choice.
Why People Confuse Them
Many English adverbs end in -ly, so learners may assume that slow cannot modify an action. However, slow is an established flat adverb—a form that works as both an adjective and an adverb without adding -ly.
All of these occur in natural American English:
“Traffic is moving slow.”
“Traffic is moving slowly.”
“Could you speak slower?”
“Could you speak more slowly?”
The versions with slowly or more slowly are broadly suitable in edited writing. The versions with slow or slower often sound more conversational, direct, or idiomatic.
Common expressions also favor slow:
“Drive slow.”
“Go slow.”
“Take it slow.”
That does not mean slow and slowly can replace each other in every sentence.
Key Differences At A Glance
| Situation | Preferred Form | Example |
|---|---|---|
| Before a noun | slow | a slow computer |
| After a linking verb | slow | The computer seems slow. |
| Formal description of an action | slowly | The computer started slowly. |
| Before an action verb | slowly | Sales slowly improved. |
| Informal command | slow or slowly | Drive slow. / Drive slowly. |
| Fixed expression | slow | Take it slow. |
| Compound adjective | slow- | slow-moving traffic |
| Verb meaning reduce speed | slow | Traffic slowed. |
| Standard comparative adverb | more slowly | Please speak more slowly. |
| Conversational comparative | slower | Please speak slower. |
Slow is a legitimate adverb in selected structures, but slowly has wider freedom of placement.
Meaning and Usage Difference
Slow as an Adjective
Slow commonly means not fast, delayed, gradual, inactive, or taking considerable time.
“A slow download interrupted the meeting.”
“The download is slow.”
“It was a slow afternoon at the store.”
“My watch is five minutes slow.”
Before a noun, use slow rather than slowly.
Slow as an Adverb
Slow can mean at a low speed:
“Drive slow on the icy road.”
“The line is moving slow today.”
This flat-adverb use is especially common after verbs and in commands. It may sound conversational or emphatic, though many expressions are firmly established.
Slow as a Verb
Slow is also a standard verb meaning to reduce speed, activity, progress, or intensity:
“Traffic slowed near downtown.”
“The medication slowed his heart rate.”
“Demand slowed in July.”
Its forms are slows, slowed, and slowing.
Slowly as an Adverb
Slowly describes an action or development happening at a low speed, over time, gradually, or cautiously:
“The file downloaded slowly.”
“The server slowly recovered.”
“Conditions are slowly improving.”
“She slowly opened the door.”
“The storm developed slowly.”
Slowly can appear before or after many verbs. Its standard comparison forms are more slowly and most slowly.
Slow uses slower and slowest as adjective forms and as accepted flat-adverb forms in suitable contexts.
Tone, Context, and Formality
Slowly is neutral and broadly suitable in professional, academic, business, and carefully edited writing:
“The committee responded slowly.”
“Drivers should proceed slowly.”
Adverbial slow often sounds more conversational, compact, idiomatic, or sign-like:
“Drive slow out there.”
“Go slow until you understand the process.”
“Take it slow during your first week.”
Commands often favor the shorter form because it sounds direct. However, school exercises and formal documents may expect slowly when an action is being modified.
Be careful when using slow to describe a person. A sentence such as “He is slow” may imply that someone has difficulty understanding and can sound insulting. Use a precise description instead.
Which One Should You Use?
First, identify what the word describes.
Use slow before a noun:
“a slow employee”
“a slow recovery”
Use slow after a linking verb when describing the subject:
“The employee seems slow.”
“The recovery was slow.”
Use slowly as the safest default when describing an action:
“The employee worked slowly.”
“The patient recovered slowly.”
Established commands and expressions may use slow:
“Please go slow.”
“Take it slow.”
A more formal version may use slowly:
“Please proceed slowly.”
Slowly is usually more natural before a verb:
“The market slowly recovered.”
Not normally: “The market slow recovered.”
Use slow as a verb when something decreases in speed:
“Sales slowed.”
Compare:
“Sales increased slowly.”
Here, slowly describes how the increase happened.
When One Choice Sounds Wrong
Slowly cannot normally describe an ordinary noun directly:
Incorrect: “a slowly computer”
Correct: “a slow computer”
Slowly is not a verb:
Incorrect: “Traffic slowlyed near the exit.”
Correct: “Traffic slowed near the exit.”
Do not replace the verb in a phrasal construction:
Incorrect: “Please slowly down.”
Correct: “Please slow down.”
Slow may sound wrong before many action verbs:
Incorrect: “The computer slow started.”
Correct: “The computer started slowly.”
The forms may also create different meanings:
“My clock runs slow.”
This means the clock loses time.
“The mechanism moves slowly.”
This describes the physical speed of its movement.
Not every post-verb use of slow is wrong. “Drive slow” is natural, while “The company responded slow to the complaint” is strongly conversational and “responded slowly” is safer in edited prose.
Common Mistakes
Believing slow is only an adjective
Incomplete rule: “Slow cannot modify a verb.”
Better rule: Slow is primarily an adjective but also functions as an adverb and verb.
Using slowly before a noun
Incorrect: “a slowly process”
Correct: “a slow process”
Automatically replacing every adverbial slow
Natural: “Take it slow.”
Do not replace established expressions mechanically.
Creating nonexistent comparison forms
Incorrect: “Please speak slowlier.”
Incorrect: “Please speak slowerly.”
Correct: “Please speak more slowly.”
Also natural in conversation: “Please speak slower.”
Using slow before a verb unnaturally
Incorrect: “The process slow improved.”
Correct: “The process slowly improved.”
Overlooking a linking verb
Incorrect: “The work seems slowly.”
Correct: “The work seems slow.”
Slow describes the work’s condition.
Hyphenating slowly moving unnecessarily
Usually correct: “slowly moving traffic”
Because an -ly adverb clearly modifies the participle, no hyphen is normally needed.
Missing the compound adjective structure
Correct: “slow-moving traffic”
Here, slow-moving forms a compound description before the noun.
Everyday Examples
Driving and Road Safety
“Traffic was slow near the airport.”
“Traffic moved slowly after the crash.”
“Drive slow on the icy road.”
“Please drive slowly through the work zone.”
Speech and Conversation
“Could you speak more slowly?”
“Could you speak slower?” is common in conversation.
“Take it slow while learning the new system.”
Technology and Work
“The app loaded slowly.”
“The app became slow after the update.”
“The office had a slow morning.”
“The team responded slowly to the request.”
Health and Recovery
“The patient’s recovery was slow.”
“The patient is slowly recovering.”
“Start slow during your first workout.”
“Gradually increase the distance.”
Business and Economics
“Economic growth slowed during the quarter.”
“Sales increased slowly in July.”
“Business was slow after the holiday.”
Cooking and Physical Processes
“Cook the beans low and slow.”
“The ice melted slowly.”
“The oven heats slowly, but it maintains a steady temperature.”
Clocks and Timekeeping
“My kitchen clock runs slow.”
“The second hand moves slowly.”
Advice and Fixed Expressions
“Go slow until you understand the instructions.”
“Slow but steady progress is still progress.”
“Slowly but surely, the repairs were completed.”
Dictionary-Style Word Details
Verb
Slow: Slow is a standard transitive and intransitive verb meaning to make something less fast or to become less fast.
“Traffic slowed near downtown.”
“The medication slowed his heart rate.”
Slowly: Slowly is not a verb. It can modify a verb but cannot carry tense. Slowlyed is not a standard form.
Noun
Slow: Slow is not commonly an ordinary standalone noun in general American English. Compounds such as slowdown, slow lane, and slow motion do not make slow itself a common noun.
Slowly: Slowly is not a noun.
Synonyms
Slow: Depending on context, close alternatives include unhurried, sluggish, leisurely, gradual, delayed, quiet, inactive, and hesitant.
Slowly: Closest alternatives include gradually, unhurriedly, leisurely, cautiously, and at a low speed.
Cautiously adds the idea of care. Gradually emphasizes development over time rather than physical speed.
Example Sentences
Slow:
“It was a slow afternoon.”
“The checkout line is slow.”
“Drive slow near the playground.”
“Sales slowed during the winter.”
“My watch runs slow.”
Slowly:
“She slowly opened the door.”
“She opened the door slowly.”
“Conditions are slowly improving.”
“A slowly developing storm approached the coast.”
Word History
Slow: Slow comes through Middle English from Old English slāw. Older meanings included inactivity, sluggishness, delay, and a lack of quick understanding. Its adjective and adverb uses have long histories.
Slowly: Slowly developed from slow plus the adverb-forming suffix -ly and has been recorded in English since the medieval period.
Phrases Containing
Slow:
- slow down
- go slow
- take it slow
- slow but steady
- slow motion
- slow-moving
- slow burn
- slow cooker
- in the slow lane
Slowly:
- slowly but surely
- move slowly
- speak slowly
- develop slowly
- recover slowly
Slowly but surely means gradual progress that is likely to succeed.
FAQs
Is Slow an Adjective or an Adverb?
Slow is primarily an adjective, but it can also be an adverb and verb.
“The car is slow” uses an adjective.
“The car is moving slow” uses a flat adverb.
Is Slowly Always Correct After a Verb?
No. Slowly is often the safest option, but established expressions use slow:
“Take it slow.”
“Drive slowly” is more formal, while “Drive slow” is also widely accepted.
Is “Drive Slow” Grammatically Correct?
Yes. Slow functions as a flat adverb in this command.
“Drive slow” sounds compact and conversational. “Drive slowly” is neutral and broadly suitable for formal instructions.
Should I Say “Speak Slower” or “Speak More Slowly”?
Both occur in American English. “Speak slower” uses the comparative flat adverb and is common in conversation. “Speak more slowly” is the safer choice in formal writing.
Is It “Take It Slow” or “Take It Slowly”?
“Take it slow” is the established expression meaning proceed carefully or without rushing. “Take it slowly” can be grammatical, but it may describe the manner of taking something and does not always carry the same idiomatic meaning.
Can Slow and Slowly Be Used Interchangeably?
Only in some sentences.
“Traffic moved slow” and “Traffic moved slowly” have similar meanings but different stylistic effects.
Before a noun, only slow works: “slow-moving traffic.”
With an -ly modifier, write “slowly moving traffic.”
Conclusion
Slow usually describes a noun or subject, but it can also function as an adverb and verb. Slowly is the regular, widely usable adverb and is generally the safest choice for formal descriptions of actions.
Keep accepted expressions such as drive slow, go slow, and take it slow. Before choosing, identify what the word modifies and where it appears:
“The bus is slow.”
“The bus moved slowly.”
“Go slow.”
“Proceed slowly.”
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