assure vs. ensure
Three words, one sound, and a division that holds up well once you see it: "assure" takes a person as its object, "ensure" takes a result, and "insure" belongs to insurance. British usage sometimes lets "insure" cover "ensure," but the person-versus-outcome split between the first two is worth keeping in any register.
assure
A verb. To tell someone something confidently, to remove their doubt. It takes a person as its object.
- I assured her the payment had been sent.
- He assured the board there was no exposure.
- Let me assure you this is temporary.
- You cannot assure a deadline — only a person.
ensure
A verb. To make certain that something happens. It takes an outcome as its object.
- Please ensure the documents are signed before Friday.
- The clause ensures the data is deleted after processing.
- We need to ensure nobody is locked out.
- Ensure takes a thing, not a person: you ensure delivery, you assure the client.
Why assure and ensure get mixed up
Assure, ensure and insure all come from the same root about making something sure, and they overlap in sound. Each has settled into its own job.
You assure a person: you tell them something confidently to remove their doubt. "I assure you the report will be ready." Assure almost always has a person as its object. Ensure means to make certain that something happens: "please ensure the doors are locked." Its object is an outcome, not a person. Insure is about insurance: arranging financial protection against loss. "We insured the shipment for its full value."
A quick check: if there is a person you are reassuring, it is assure. If you are guaranteeing a result, it is ensure. If money and a policy are involved, it is insure.
Common mistakes
I can ensure you the invoice was paid on time.
✓I can assure you the invoice was paid on time.
You are reassuring a person, so assure.
Please assure that every form is signed.
✓Please ensure that every form is signed.
The goal is to make an outcome certain, so ensure.
You'll need to ensure the car before you drive it home.
✓You'll need to insure the car before you drive it home.
Buying coverage is insure.
Quick way to remember
Ask what follows the verb. A person follows "assure" — you assure someone. A result follows "ensure" — you ensure something happens. And if money changes hands against a risk, it is "insure."
Questions
Is insure ever used to mean ensure?
In American English, yes, sometimes ("to insure accuracy"), and it is not strictly wrong. Keeping insure for insurance and using ensure for everything else is clearer, and that is what most style guides recommend.
What is the noun for assure?
Assurance: "she gave us her assurance." In British English, "life assurance" is also a type of insurance, but in the US that is called life insurance.