Some style guides declare that INSURE, ENSURE, and ASSURE can be used interchangeably. But some do not! What's a writer to do when even the experts don't agree? This writer has a method for distinguishing them, and I'm happy to share.
Let's start with synonyms for each.
INSURE: Protect, guarantee, or essentially, offer insurance. Notice how INSURE is the root word in INSURANCE? Bingo!
ENSURE: Make sure, confirm, verify, secure, and guarantee. Oh no! Do you notice how guarantee shows up as a synonym for both words?
ASSURE: reassure, pledge, promise, guarantee, secure, ENSURE.
If you follow a particular style guide, I suggest you obey its rules. But if not, use INSURE when you're referring to insurance. Phew! That's one down.
Notice how ENSURE and ASSURE are listed as synonyms? Both could be used in the following sentence, but my choice goes with ENSURE when my intent is to make sure or guarantee.
I conferred with my fellow troublemakers to ENSURE they kept the record straight.
In my humble opinion, ASSURE is best used to convey a promise or reassurance, rather than an ironclad guarantee. You can ASSURE someone you're telling the truth or ASSURE that you'll complete your responsibilities for a group project. I ASSURE YOU sounds better than I ENSURE YOU or I INSURE YOU. Here's an example:
I ASSURE YOU I'll write you a glowing recommendation letter, as you truly deserve it.
If you're still feeling less than REASSURED, I leave you with these sage words from www.merriam-webster.com:
If you still feel uncomfortable and itchy when trying to decide if it is correct to assure your spouse that you will ensure that the new job will leave you insured, you can relax. Even in the judgy and nitpicky world of English usage if you choose the wrong one here it’s more of a venial sin than a mortal one.
(P.S. Venial means forgivable!)
I ASSURE you this spoonful is now finished.
Laura Fineberg Cooper
A Spoonful of Grammar