The verbs assure, ensure, and insure all mean "to make certain or secure." According to Merriam-Webster's Collegiate Dictionary, "insure sometimes stresses the taking of necessary measures beforehand, and assure distinctively implies the removal of doubt and suspense from a person's mind."
In addition, insure means "to protect against financial loss," and assure, which is almost always used with reference to people, generally means "to promise." For some finer distinctions (and disagreements), see the usage notes below.
- "Do not worry about your problems with mathematics. I assure you mine are far greater." (Albert Einstein)
- The USDA must act to ensure safety in school lunch programs.
- She has not been able to insure her Bugatti, a valuable old car.
- "Use ensure to mean guarantee: Steps were taken to ensure accuracy.
"Use insure for references to insurance: The policy insures his life."
(Norm Goldstein, "ensure, insure," The Associated Press Stylebook, 2006)
- "A few commentators . . . suggest assure for people, ensure for things, and insure for money and guarantees (insurance). These are nice distinctions, and you can follow them if you want to. . . .
"The rest of the recommendation rests on using ensure for general senses and reserving insure for financial senses. This distinction has been urged at least since Fowler 1926, especially by British commentators. It is in general true that insure is used for the financial uses (it must vex the British commentators to find assure still occasionally used in this sense by British technical writers). However, both insure and ensure are used in general senses. . . .
"Our most recent evidence shows that the distinction between ensure and insure is made more often in British written English than in American written English, and a few commentators hold that insure is more common than ensure in American English."
("ensure, insure, assure," Merriam-Webster's Dictionary of English Usage, 1994)
- "A person assures (makes promises to, convinces) other people . . .; a person ensures (makes certain) that things occur or that events take place . . .. To put it a little technically, if the verb is in the active voice, a predicate beginning with that should be introduced by the verb ensure."
(Bryan A. Garner, Garner's Modern American Usage, Oxford University Press, 2003)
- "European 'life assurance' companies take the position that all policy-holders are mortal and someone will definitely collect, thus assuring heirs of some income. American companies tend to go with 'insurance' for coverage of life as well as of fire, theft, etc."
(Paul Brians, Common Errors in English Usage, William, James & Co., 2003)
(a) Don't _____ your car for every nick and scratch.
(b) "In real life, I _____ you, there is no such thing as algebra." (Fran Lebowitz)
(c) Federal drug regulators need more power and money to _____ the safety of the nation’s drug supply.