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Lots of folks use “insure,” “ensure,” and “assure” interchangeably, especially in their speech. While these words sound similar and represent similar ideas, there’s no situation in which they could mean exactly the same thing.

Luckily, once you know the difference, it’s an easy mistake to avoid.

When to use Ensure

To ensure something or someone is to guarantee something will happen. It’s a promise of a future result. You may substitute the word “guarantee” to ensure you are using this word correctly in your writing.

  • I brush and floss my teeth every night to ensure my gums will stay healthy.

  • A bouquet of roses will ensure that your wife knows you were thinking about her this Valentine’s Day.

  • Rob ensured his online safety by changing his password.

  • Regular oil changes and maintenance ensure your car will last over 200,000 miles.

  • Kelly made flashcards to ensure she would make a good grade on her exam.

Notice, some of the objects of “ensure” in these sentences are a little abstract. However, they are all the future result of something in the present.

When to use Insure

To insure something or someone is to cover it with an insurance policy.

The shared “in” beginning can help you remember.

  • It was hard to find someone who could insure my boat.

  • In the Midwest, most homes are insured against tornados.

  • It’s against the law to not insure your car.

  • There was a rumor floating around that the pop star had insured her legs.

  • Kevin’s current policy doesn’t insure his visits to the dentist.

Notice, if you substitute “guarantee” for “insure,” these sentences do not retain their meaning. In fact, they cease to make sense at all. Additionally, the grammatical objects of “insure” in these sentences are much simpler.

When to use Assure

To assure someone is to lessen their doubt. The object of “assure” will always be a person.

  • I assure you, I did not mean to step on your cat’s tail.

  • Jane assured Mike she had locked the door by giving the knob a quick turn.

  • When he asks for a raise, Ron will assure his boss that he will continue to work hard for the agency.

  • Marissa assured her mom that she had studied and was ready for her test tomorrow.

  • After the water pipes burst for the fifth time that winter, Mayor Johnson assured the town’s residents that the pipes would be fixed.

In each of these sentences, the thing being assured is a person or group of people. Of the three, “assure” is the easiest to remember—all you have to do is locate who is assuring whom.

Pop Quiz

Here are a few sentences to check your understanding.

  • Though Emily had only met her fiancé’s mother once, it was enough to (assure, ensure, insure) her that Emily would be a good partner.

  • Check the phone book to find a company that can (assure, ensure, insure) your storage building.

  • James (assures, ensures, insure) his dog gets enough exercise by running with her each morning.

  • Sally stayed up all night drafting a policy to (assure, ensure, insure) her client’s hovercraft.

  • We will (assure, ensure, insure) our victory over the school across town by practicing every day this summer.

  • I need to be (assured, ensured, insured) that you can deliver the package to me on time.

  • (Assure, ensure, insure) you have enough grain to last through the winter by saving 10 percent of each field you harvest.

  • We need to leave soon because Rick (assured, ensured, insured) Layla we would arrive at the play on time.

  • Allen’s company doesn’t (assure, ensure, insure) small planes.

  • The computer technician (assured, ensured, insured) Jaye that it wasn’t a virus that was causing the problem, but Jaye is still doubtful.

Answers: 1. assure, 2. insure, 3. ensures, 4. insure, 5. ensure, 6. assured, 7. ensure, 8. assured, 9. insure, 10. assured.