Although these three often show up at the same party to give out hugs, they are not the same thing. "To assure" means to convince, inform positively or give confidence to, "to ensure" means to make something certain to happen, and "to insure" means to make sure you're financially secure. Does that make sense? Do you understand it now, and are you sure about that?
"To assure" means to remove doubt or to tell someone something confidently. It is usually followed by an object, i.e., you are giving someone assurance.
You can also tell someone they can "rest assured" because you know everything is under control:
On the other hand, "to ensure" means to make sure that something happens or is definite:
Lastly, use "insure" when you need insurance. "To insure" means to arrange financial compensation for the loss of something, or in case someone is injured or dies. You could insure your health, your Cadillac, your condo at the beach, or your stocks and bonds:
Sometimes people say "ensure" or "insure" when they actually mean "assure," to avoid doubt or confusion. Bryan Garner points out in Garner's Modern American Usage that this usage has become ubiquitous.
Oh, dear! We assure you that there is a difference, and by reading this article, you have ensured that you know your way around these tricky words, but unfortunately, we cannot insure you. It's just not that kind of party.
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