Adjective B1 — Intermediate /ˈsɜː.tən/

Certain — Definition, Examples & Usage

Sure and definite, with no room for doubt — or a particular thing you do not need to name.

Quick Definition

Certain (adjective) — 1. completely sure and definite; having no doubt about something. 2. particular but not named or specified. Example: I am certain that the meeting is on Thursday.

What Does Certain Mean?

Certain comes from Old French certain, derived from Vulgar Latin certanus and ultimately from Latin certus meaning "settled" or "resolved". The Latin root cernere (to sift or decide) also gives us discern, concern, and secret. The word entered English in the 13th century and has been in continuous everyday use ever since.

In modern British English, certain carries two distinct meanings that learners must keep apart. The first, and more common, sense expresses complete confidence or absence of doubt: I am certain she is right. The second acts as a determiner, pointing to something particular without naming it directly: A certain colleague of mine disagrees. This second use often gives writing a deliberately formal or slightly mysterious tone.

The word family is especially productive: the adverb certainly is one of the most frequent words in English, and the nouns certainty and uncertainty appear constantly in academic, journalistic, and professional writing. Mastering certain therefore unlocks a whole cluster of high-frequency vocabulary.

Example Sentences

Sentence Level Usage note
I am certain that the meeting is on Thursday. A2 certain + that-clause; basic personal conviction
Are you certain you locked the door before leaving? B1 certain in a question; followed by subject + verb
There are certain rules that every employee must follow. B1 certain as determiner; meaning "particular but unspecified"
It seems almost certain that prices will rise next year. B2 almost certain; impersonal construction with "it"
The outcome, while not guaranteed, is by no means certain to disappoint. C1 by no means certain; formal, nuanced register

Collocations

Collocation Example
feel certain I feel certain we have met before.
make certain Please make certain you have your passport with you.
almost certain It is almost certain that the flight will be delayed.
absolutely certain I am absolutely certain this is the correct address.
by no means certain Victory is by no means certain at this stage.
a certain amount of The job requires a certain amount of patience.
under certain conditions The agreement is valid only under certain conditions.
certain to happen Change is certain to happen sooner or later.
say with certainty I cannot say with certainty when he will arrive.
for certain Nobody knows for certain what the future holds.

Usage Notes

Certain + that-clause. When certain expresses conviction, it is commonly followed by a that-clause: She is certain that he will pass. In informal speech, that is often dropped: I'm certain he'll be late. Both forms are correct.

Certain + infinitive. In impersonal constructions, certain is followed by the infinitive: The plan is certain to succeed. This pattern is especially common in journalism and formal writing. Do not confuse it with the determiner use: a certain plan simply means a particular, unnamed plan.

Certain vs. sure. In British English, sure is the more casual option (I'm sure it's fine) while certain feels more deliberate and emphatic (I am certain this is correct). In formal writing, certain is generally preferred. Note that sure cannot act as a determiner — you cannot say a sure colleague to mean an unspecified colleague.

Adverb: certainly. The adverb certainly is used both to express strong agreement (Certainly, I will attend) and as a sentence adverb to reinforce a claim (She will certainly succeed). Be careful not to overuse certainly in formal essays, where it can weaken rather than strengthen an argument if every claim is labelled "certain".

Common Mistakes

Watch Out For

I am certain about that he will come.

I am certain that he will come. (do not use "about" before a that-clause)

She is certain of passing the exam. (non-standard in British English)

She is certain that she will pass the exam. (use a that-clause in British English)

He is certain to passes the exam.

He is certain to pass the exam. (certain + bare infinitive, not third-person -s)

There are certains rules you must follow.

There are certain rules you must follow. (certain as determiner has no plural form)

Related Words

certainly (adverb) certainty (noun) uncertain (adjective) uncertainty (noun) sure definite confident convinced positive doubtful

Practise This Word

Flash Cards Complete the Sentence Vocabulary Quiz Hangman

Frequently Asked Questions about “certain”

What does certain mean in English?
Certain has two main meanings. First, it means completely sure or confident: 'I am certain he will come.' Second, it means a particular but unspecified thing or person: 'a certain colleague of mine'. Both meanings are very common in everyday English.
What is the difference between certain and sure?
Sure and certain are very close in meaning, but certain tends to be slightly more formal. 'I am sure' is natural in casual speech, while 'I am certain' sounds more deliberate and emphatic. Certain can also act as a determiner ('a certain person'), whereas sure cannot.
How do you use certain in a sentence?
Certain can follow a linking verb: 'She is certain about the answer.' It can also precede a noun as a determiner: 'There are certain rules you must follow.' When followed by a clause, use 'that': 'I am certain that he left early.'
What is the adverb form of certain?
The adverb is 'certainly', used to express strong agreement or confidence: 'Certainly, I will help you.' It is also used as a sentence adverb: 'She will certainly pass the exam.' Avoid confusing 'certainly' with 'surely', which can imply doubt in British English.
What is the noun form of certain?
The noun form is 'certainty': 'There is no certainty about the outcome.' The plural 'certainties' refers to things that are guaranteed: 'Death and taxes are two certainties in life.' The negative noun form is 'uncertainty'.
What is the difference between certain and definite?
Both mean fixed or sure, but they are used slightly differently. Definite usually describes plans, facts, or arrangements: 'We have a definite date for the meeting.' Certain is more personal, relating to a person's conviction: 'I am certain this is the right answer.' You would not normally say 'I am definite'.
Can certain be used as a determiner?
Yes. As a determiner, certain means 'particular but not named': 'A certain person called for you.' This use softens the reference deliberately, often adding a slightly formal or mysterious tone. It always comes before the noun and is followed by the noun directly or by 'a/an'.
What are common collocations with certain?
Common collocations include: feel certain, make certain, almost certain, absolutely certain, by no means certain, a certain amount of, under certain conditions, and certain to happen. The phrase 'make certain' is especially useful and means to ensure or double-check something.
What is the origin of the word certain?
Certain comes from Old French 'certain', from Vulgar Latin 'certanus', derived from Latin 'certus' meaning 'settled, resolved, sure'. The Latin root 'cernere' (to sift, decide) also gives us 'discern', 'concern', and 'secret'. Certain entered English in the 13th century.
How can I practise using certain in English?
Use LexFizz's Complete the Sentence exercise to practise certain in context. The Flash Cards tool will help you memorise certain and its word family (certainly, certainty, uncertain, uncertainty). Writing your own sentences using 'I am certain that…' is also an excellent active learning technique.