One of our readers recently asked about the differences between assure, ensure, and insure. All three of these words ultimately derive from the Latin word sēcūrus meaning “safe.” As with many words that share ancestors, these terms’ meanings overlap thematically, but they’re not necessarily interchangeable. Here’s a look at the key differences.

Assure was the first of the three to enter English with a reflexive sense of “to have confidence, trust, rely.” Today, the term is most commonly used to mean “to state with confidence to” or “to cause to know surely,” conveying the action of putting someone’s mind at ease, as in She assured us that everything would turn out all right.

Ensure entered English shortly after assure with the meaning “to declare earnestly to; state with confidence to.” Today it is widely used to convey the action of securing or guaranteeing an outcome or development, as in This letter will ensure you a hearing.

Insure entered English as a variant of ensure. However, in the mid-1600s, insure picked up a financial sense of “to pay a sum to secure indemnity to or on, in case of loss, damage, or death.” This financial sense is what distinguishes it today. Nowadays, we primarily use insure to talk about providing or obtaining insurance, as in After all his car accidents, the company refuses to insure him again. Insure can be used to talk about other kinds of risk, but in that usage, the term is typically followed by the word against, as in We insured against disappointment by making an early reservation.

As you can see, all of these terms address the action of making certain or guaranteeing, but each in a slightly different way. The most important distinction to remember when trying to decide which to use is that insure is the only of the three that explicitly refers to insurance policies and financial risk.

Examples of insure in a Sentence

He found the language not obscene … but did find it intentionally disruptive, and held that school officials had the right to insure that a high-school assembly proceed in an orderly manner, without hoots and howls and all that snickering. —William Safire, New York Times Magazine, 24 Aug. 1986
… his sudden fame probably insured a backlash. —Calvin Tomkins, New Yorker, 6 Dec. 1982
The fact that by supplying his uncle with an amusing mistress he would insure against any awkward second marriage was merely a fortunate coincidence. —Mollie Hardwick, Emma, Lady Hamilton, 1969
We insured our house against fire and flood damage.

I found a company that will insure my car for less than I’ve been paying.

This policy will insure your car against theft.

She had difficulty finding a company that would insure her.

They take great care to insure the safety and security of their home.

We hope that careful planning will insure success.
Recent Examples of insure from the Web
There are other ways to insure against a crash than buying bonds.

The Economist, «Why it makes sense to invest in Treasury bonds,» 26 May 2018
And many species that have an enormous value to ocean ecosystems, such as crucial oxygen-generating bacteria, do not have easily quantifiable benefits to humanity, so are difficult to insure.

Emma Farge, The Christian Science Monitor, «Natural ocean barriers could soon be covered by insurance,» 15 May 2018
On February 20, 1996, Matsch had ruled that McVeigh’s trial would be moved from Oklahoma City to Denver, to insure an impartial jury.

Jill Lepore, The New Yorker, «The Rise of the Victims’-Rights Movement,» 14 May 2018
Do you ensure or insure?
There is considerable confusion about whether ensure and insure are distinct words, variants of the same word, or some combination of the two. They are in fact different words, but with sufficient overlap in meaning and form as to create uncertainty as to which should be used when. We define ensure as “to make sure, certain, or safe” and one sense of insure, “to make certain especially by taking necessary measures and precautions,” is quite similar. But insure has the additional meaning “to provide or obtain insurance on or for,” which is not shared by ensure. Some usage guides recommend using insure in financial contexts (as in “she insured her book collection for a million dollars”) and ensure in the general sense “to make certain” (as in “she ensured that the book collection was packed well”).

Synonym Discussion of insure

ensure, insure, assure, secure mean to make a thing or person sure. ensure, insure, and assure are interchangeable in many contexts where they indicate the making certain or inevitable of an outcome, but ensure may imply a virtual guarantee ⟨the government has ensured the safety of the refugees⟩ , while insure sometimes stresses the taking of necessary measures beforehand ⟨careful planning should insure the success of the party⟩ , and assure distinctively implies the removal of doubt and suspense from a person’s mind. ⟨I assure you that no harm will be done⟩ secure implies action taken to guard against attack or loss. ⟨sent reinforcements to secure their position⟩