To business. “Assure,” “ensure,” and “insure” have similar sounds. They even have similar definitions and occasionally can be used interchangeably. In such instances, the words are used to indicate that something is certain or to make a person feel sure.
Such instances are rare; the three words have slight variations to their definitions that affect their connotations. To “assure” someone is to remove doubt or suspense from his or her mind. If I say, “I assure you he won’t be late,” I may be telling the truth as far as I know it. My real aim, though, is to reassure the person to whom I’m speaking.
“Ensure” indicates a guarantee. It’s a cause-and-effect relationship. One action is taken so that another will occur. In many cases, “ensure” plays a similar role to “so that” or “in order to”:
We left early so that we wouldn’t be late.
We left early in order to arrive on time.
We left early to ensure we arrived on time.
“Insure” is the least common of the three words, probably because it tends to be found in financial or legal circles. It means to take necessary measures before an event, either good or bad. In insurance, one would “insure” himself or herself against hail damage. A person’s careful planning should “insure” the success of a party. It’s an unlikely use of the word; it’s more likely that a person will take steps to “ensure” the success of a party.
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