Sure (adjective) means confident that something is true or that something will happen. As an adverb, it means certainly or of course. It is also used in fixed phrases such as make sure, for sure, and sure enough.
What Does Sure Mean?
Sure comes from Old French sur (safe, secure), derived from Latin securus (free from care) — the same root that gives us secure and security. It entered English in the 14th century with the sense of "safe" or "reliable", and gradually shifted towards the modern meaning of "confident" or "certain".
As an adjective, sure describes a state of certainty or confidence: Are you sure about that? It can also describe something dependable or guaranteed: a sure sign of rain, a sure way to improve your score. In this second sense it is close to reliable or definite.
As an adverb, sure is used informally to mean "certainly" or "of course", particularly in conversational responses: Can you help? — Sure! The more formal adverb form is surely, which carries a slightly different nuance — it often expresses the speaker's strong expectation or mild surprise.
The phrase make sure is especially important for English learners. It means to check that something is done correctly or that something is the case. It is followed by a that-clause (where that is often omitted in speech): Make sure you lock the door. This structure is extremely common in instructions, reminders, and written guidance.
Example Sentences by CEFR Level
| Sentence | Level & Note |
|---|---|
| Are you sure this is the right bus? | A2adjective — asking for confirmation |
| Make sure you check for agreement between the subject and verb. | B1make sure + that-clause (that omitted) |
| She was not sure whether to accept the job offer or wait for a better one. | B1sure + whether-clause expressing uncertainty |
| I am not entirely sure of the legal implications, so I would recommend consulting a solicitor. | B2sure + of + noun phrase; formal register |
| The rising cost of living is a sure indicator that monetary policy adjustments are inevitable. | C1sure as adjective meaning reliable/definite; academic/formal writing |
Collocations
| Collocation | Example |
|---|---|
| make sure | Make sure you arrive on time for the interview. |
| for sure | I don't know for sure when the results will be published. |
| sure enough | I expected problems, and sure enough, the system crashed. |
| be sure to | Be sure to save your work before closing the application. |
| not sure whether / if | He was not sure whether the meeting had been rescheduled. |
| pretty sure | I'm pretty sure I left my keys on the kitchen table. |
| quite sure | Are you quite sure you want to submit this draft? |
| a sure sign | Dark clouds are a sure sign that rain is on the way. |
| sure thing | "Could you proofread this?" — "Sure thing." |
| sure-fire | Regular reading is a sure-fire way to expand your vocabulary. |
Usage Notes
How to Use Sure Correctly
- sure vs. surely: As an adverb, sure is informal (mainly spoken). Use surely in formal writing to express strong expectation: Surely there is a simpler solution.
- sure vs. certain: Both mean confident or definite. Certain is slightly more formal and emphatic; sure is more conversational. In formal writing, prefer certain.
- make sure + that-clause: The conjunction that is usually omitted in speech: Make sure you read the instructions carefully. In formal writing, including that is acceptable: Make sure that all fields are completed.
- sure as an adverb in British English: Using sure alone to mean "of course" (e.g., "Sure, I can do that.") is more common in American English. British speakers more often say of course, certainly, or no problem.
- sure + of vs. sure + about: Both patterns are correct but have slightly different uses. Sure of often follows a specific noun or pronoun: I am sure of that. Sure about is more common before noun phrases and clauses: Are you sure about your answer?
Common Mistakes
Watch Out For
I am sure of that he will pass. (do not combine "of" and a that-clause)
I am sure that he will pass. / I am sure of his success.
Surely I am not sure about the answer. (do not mix "surely" and "sure" in the same clause)
I am not sure about the answer. / Surely someone knows the answer.
Make sure to checking the grammar before you submit. (make sure is followed by an infinitive or that-clause, not a gerund)
Make sure to check the grammar before you submit. / Make sure you check the grammar.