Vocabulary
B2
6 min read
Updated 15 June 2026
Quick Answer
Assure means to tell someone something positively to remove their doubt or worry — it always has a person as its object: I assure you it’s safe. Ensure means to make certain that something happens — it takes a fact or result: please ensure the door is locked. You assure a person; you ensure an outcome. (A third word, insure, relates to insurance.)
Assure and ensure sound almost identical and both involve making something certain, which is why they get swapped. The clean distinction is who or what receives the action. Assure is about people: you give them confidence and remove their doubt. Ensure is about outcomes: you guarantee that something will happen. A closely related third word, insure, deals with financial insurance. Keeping the objects straight is the key.
At a Glance: Assure vs Ensure
| Word | Part of Speech | Pronunciation | Core Meaning |
|---|
| assure |
verb |
/əˈʃʊə/ |
to tell someone confidently so they feel certain or less worried |
| ensure |
verb |
/ɪnˈʃʊə/ |
to make certain that something happens or is the case |
Using “Assure”
Assure means to tell someone something firmly and positively so that they feel certain or stop worrying. Its object is always a person (or people): I assure you, she assured the customer. It is closely linked to reassure, to comfort someone again.
When to use it
- Removing someone’s doubt: I assure you it will be fine
- Always with a person as object: he assured his boss
- Giving a promise or guarantee to someone: they assured us of their support
- Linked to reassurance and confidence
- Related words: assurance, reassure, self-assured
I can assure you that your data is completely safe.
The manager assured the customers of a full refund.
She assured me she would arrive on time.
“There’s nothing to worry about,” he assured her.
They assured us of their continued support.
Using “Ensure”
Ensure means to make certain that something happens or is true. Its object is a thing, fact, or outcome, not a person: ensure the door is locked, ensure success. It is about guaranteeing a result through action.
When to use it
- Making a result certain: ensure the meeting starts on time
- Object is a fact or outcome: ensure that everyone is safe
- Often followed by “that”: ensure that the form is signed
- Guaranteeing through action or checking
- Related: distinct from insure (insurance)
Please ensure all the windows are closed before you leave.
Careful planning will ensure the event runs smoothly.
We must ensure that every child is accounted for.
Back up your files to ensure nothing is lost.
Good training helps ensure a safe workplace.
The Key Difference
Look at the object. Assure takes a person: you make someone feel sure (I assure you). Ensure takes a result: you make something certain to happen (ensure the door is locked). If you could add the word that and a result, it is ensure; if there is a person who feels reassured, it is assure. Watch out for the third sibling, insure, which is about insurance policies.
Memory Tip
aSSure aims at a perSon (you reaSSure Someone). eNsure makes certaiN that someThing happeNs — it points at an outcome, not a person. And insure hides insurance. Person → assure; result → ensure; money/policy → insure.
Common Mistakes
Please assure that the door is locked.
Please ensure that the door is locked. (making a result certain is ensure)
I ensure you there is nothing to worry about.
I assure you there is nothing to worry about. (telling a person to remove doubt is assure)
Good planning will assure the project succeeds.
Good planning will ensure the project succeeds. (guaranteeing an outcome is ensure)
The waiter ensured the guests their meal was free.
The waiter assured the guests their meal was free. (reassuring people is assure)
Frequently Asked Questions
What is the difference between assure and ensure?
Assure means to tell someone something confidently so they feel certain or stop worrying, and it always takes a person as its object: I assure you it is safe. Ensure means to make certain that something happens or is true, and it takes a result or fact: please ensure the door is locked. The simplest rule is that you assure a person but ensure an outcome. A handy check is whether there is a person being reassured or a result being guaranteed.
Is it 'ensure' or 'assure' that the door is locked?
It is ensure. Making certain that the door is locked is about guaranteeing a result, not reassuring a person, so the correct verb is ensure: please ensure that the door is locked. You would only use assure if a person were the object, as in I assure you the door is locked, where you are removing someone's doubt. Whenever the object is a fact or outcome introduced by that, ensure is almost always the right choice.
What is the difference between ensure and insure?
Ensure means to make certain that something happens: ensure the form is signed. Insure means to arrange financial protection through an insurance policy: insure your car against theft. They sound similar and share spelling, but insure specifically relates to insurance and paying compensation for loss or damage. In British English the line is fairly clear, while American English sometimes uses insure for ensure too. For making something certain, ensure is the safe, standard choice; for insurance, use insure.
Can you assure a result instead of a person?
In standard usage, no. Assure normally takes a person as its object, because it means to make someone feel certain or to remove their doubt: she assured the customer. To talk about making a result certain, you use ensure, which takes a fact or outcome: she ensured the order was correct. There is an older, more formal pattern, assure someone of something, as in he assured us of his support, but even there the direct object is still a person.
Is it 'I assure you' or 'I ensure you'?
It is I assure you. When you are speaking directly to a person to remove their doubt or worry, you assure them, so the correct form is I assure you, for example I assure you there is nothing to worry about. I ensure you is incorrect, because ensure takes a result, not a person. If you wanted to use ensure, you would need an outcome, such as I will ensure your order arrives on time, with no personal object after the verb.
How do you pronounce assure and ensure?
Assure is pronounced /əˈʃʊə/, roughly uh-SHOOR, beginning with a soft uh sound. Ensure is pronounced /ɪnˈʃʊə/, roughly in-SHOOR, beginning with an in sound. Both end in the same shoor sound, which is why they are easy to confuse by ear. The main audible difference is the opening: the uh of assure versus the in of ensure. Insure sounds very similar to ensure, so context and meaning usually matter more than sound here.
What is the difference between assure and reassure?
Assure means to tell someone something confidently so they feel certain, often for the first time. Reassure means to do this again, or to comfort someone who is anxious by removing their worry, as in she reassured the nervous patient. The re- prefix adds the sense of restoring calm or confidence. Both take a person as their object, so they belong to the same family. If someone is already worried and you calm them, reassure is often the more natural word.
Which preposition follows assure and ensure?
Assure is often followed by of when giving a guarantee to a person: he assured us of his support. It can also be followed directly by a that clause: she assured me that it was safe. Ensure is most commonly followed by a that clause stating the result: please ensure that the gate is closed. You can also drop that: ensure the gate is closed. So assure pairs with of or that, while ensure typically takes that and a result.
Why are assure and ensure so easily confused?
They are confused because they sound nearly identical, both end in the shoor sound, and both involve the idea of making something certain. The crucial difference, that assure aims at a person while ensure aims at a result, is easy to overlook in fast speech. Add the lookalike word insure, about insurance, and the trio becomes a classic trap. The fix is to focus on the object: a person you reassure, a result you guarantee, or an insurance policy.
How can I remember which verb to use?
Match the verb to its object. Assure aims at a person, and both contain a strong s sound, so think you reassure someone. Ensure makes certain that something happens, so think ensure equals make certain of an outcome. Insure hides the word insurance, so use it for policies and money. In short: person points to assure, result points to ensure, and insurance points to insure. Check what the verb is acting on, and the right choice becomes clear.
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