If you often see ensure and insure used interchangeably, or you yourself confuse the words, rest assured, you’re not alone. The words’ definitions overlap considerably: “Ensure” means to make certain, and one meaning of “insure” is to make certain by taking necessary action. Choosing the correct word based on these definitions alone requires careful precision.
But, because “insure” has another commonly used meaning related to insurance, you can draw a clearer line when it comes to deciding which word to use. Many usage manuals, including the Annenberg Style Guide that powers Stylebot, take this opportunity and advise that “ensure” should be used to mean to make certain and that “insure” should refer to insurance.