Christina Vasilevski

Certain words – no matter how hard editors or other language mavens may try – will always cause confusion because they are different from, but closely related to, words with similar meanings. Most of the time, this problem occurs in pairs: “comprise” versus “compose,” “imply” versus “infer“, and so on. But today, we’re going to tackle something a little different, and instead focus not on a pair, but on a trio of words that cause confusion: “assure,” “insure” and “ensure.” First off, the definitions, all provided by the fourth edition of the American Heritage Dictionary of the English Language.

assure (verb)
1. To inform positively, as to remove doubt: assured us that the train would be on time.
2. To cause to feel sure: assured her of his devotion.
3. To give confidence to; reassure.
4. To make certain; ensure: “Nothing in history assures the success of our civilization” (Herbert J. Muller).
5. To make safe or secure.
6. Chiefly British To insure, as against loss.

ensure (verb)
To make sure or certain; insure: Our precautions ensured our safety. See Usage Note for assure (above).

insure (verb)
1.
a. To provide or arrange insurance for: a company that insures homeowners and businesses.
b. To acquire or have insurance for: insured herself against losses; insured his car for theft.
2. To make sure, certain, or secure. See Usage Note for assure (above).

v.intr.
To buy or sell insurance.

On the surface, all three of these words have a similar concept at heart: that of safety, reinforcement, and protection. And why not? All three words are derived from the Latin word “securus,” meaning “safe” or “secure.” Furthermore, American Heritage 4 says that “assure” can be used interchangeably with the other two words, and even that “insure” can  be used interchangeably with “ensure.”

So what are the differences? They’re mainly ones of nuance. To me, the word “assure” evokes the idea of psychological security, as outlined in the first three definitions of “assure” that were listed above:

• You can rest assured that Mighty Mouse will come to save the day
• Laurie assured me that she had everything under control

As a side note, I find it interesting that the definition above states that “assure” and “reassure” mean the same thing, because then it seems that my dictionary is inconsistent. American Heritage 4 has this to say about “reassure”:

re·as·sure (verb)
tr.v. re·as·sured, re·as·sur·ing, re·as·sures
1. To restore confidence to.
2. To assure again.
3. To reinsure.

If we take these definitions at face value, “assure” means “to reassure,” which means “to assure again” – which means that “to assure” means “to assure again.” Maybe I’m reading everything wrong, but isn’t this rather tautological? Shouldn’t dictionaries try to guard against such things?

No matter – onwards we go!

If “assure” implies psychological security, then “insure” implies financial or economic security. Buying life insurance or home insurance means putting an economic safeguard in place if your house burns down, or if you die: your family gets some sort of financial compensation for bad things happening.

Finally, if “assure” relates to psychological security, and “insure” relates to financial security, what does “ensure” relate to? I feel pretty comfortable saying that “ensure” relates to most other tangible and intangible forms of security:

• Please ensure that your seat belt is buckled during take-off and landing
• Loretta, by agreeing to be my child’s babysitter, you ensure that my child will be safe while I’m at work
• We must ensure that the important company report is delivered to Mr. Calhoun by Tuesday

So, there we have it. There are other websites you can visit to get a better handle on this particular issue; I highly recommend Grammar Girl if you’re looking for an explanation that is more compact.