I was editing some copy this morning from a US client and the word "insure" was used in the context of "guarantee" - as in "we want to insure that our customers love our products". My instinct was to replace this with "ensure", but then I wondered "hmm .. is this an American/Canadian thing. Do I think the 'e' is fancier so I'd rather use it? What is correct?"
Sadly, my regular grammar go-to is on holiday, so I asked the internets. And who has the best answer? Grammar Girl, of course! She says (via guest post from Charles Carson) ...
The verbs assure, ensure, and insure all have the general meaning "to make sure," and even though some argue that they are interchangeable (1,2), many maintain that their usage is dependent on context (3,4,5,6):
Assure is something you do to a person, a group of people, or an animal to remove doubt or anxiety, as in Squiggly assured Aardvark that he'd come to the party early. You can remember that assure can only be used with things that are alive (and both assure and alive start with a). Only things that are alive can feel doubt or anxiety, so only they can be assured.
Ensure is something you do to guarantee an event or condition, as in To ensure there'd be enough food, Aardvark ordered twice as much food as last year. You can remember that guarantee has those two e's on the end to help you remember that to ensure (with an e) is to guarantee something.
Insure can be done to a person, place, or thing, but it's reserved for limiting financial liability, most commonly by obtaining an insurance policy, as in Aardvark wondered if the caterers were insured against loss. You can remember that we take out insurance to protect our income if we become unemployed, disabled, or injured in an accident. Both insure and income begin with -in.
There is more info over at the article, including rifs on "secure" and "reassure". Interesting stuff.
Photo Credit: 1f2frfbf on Flickr