Are you speaking of US English or British English? The answers are different for each language.

In British English each of these three words has a different meaning.

Richard English

To make this post a bit shorter than it could be, I am only listing the 3 definitions I found in AHD that are similar for these words, there are other difinitions, however.

insure 2. To make sure, certain, or secure. See Usage Note at assure.

ensure To make sure or certain; insure: Our precautions ensured our safety. See Usage Note at assure.

assure 4. To make certain; ensure: “Nothing in history assures the success of our civilization” (Herbert J. Muller).

USAGE NOTE: Assure, ensure, and insure all mean “to make secure or certain.” Only assure is used with reference to a person in the sense of “to set the mind at rest”: assured the leader of his loyalty. Although ensure and insure are generally interchangeable, only insure is now widely used in American English in the commercial sense of “to guarantee persons or property against risk.”

Since our votes run against the thinking of the AHD 100% thus far, whether English or US, I say we write and protest their claims!

Collins English Dictionary specifically lists 'insure' as being a synonym for 'ensure' in US English but not in UK English where it is only listed with the meaning 'to guarantee or protect (against risk, loss etc): we insured against disappointment by...'.
The meanings listed for 'assure' are all quite different from the ones for 'insure' or 'ensure' and there is no usage note suggesting that US English is different.

si hoc legere scis nimium eruditiones habes

Read all about my travels around the world here.

I was taught that "insurance" was taken out against eventualities that might happen. This would be cover on houses, cars, etc. "Assurance" was taken out on something that would happen eventually. The only question being when. This basically means death cover.

"Ensure" has a totally different meaning, to make certain.

There is a similar confusion about enquire and inquire.

* Edited to correct typo.

[This message was edited by arnie on Thu Sep 26th, 2002 at 20:42.]

Arnie's definitions are as I learnt them and I believe correct for UK English.

The OED suggests that there is a nice distinction between "enquire" and "inquire" (and between enquiry and inquiry)

Enquire, it suggests, is best used to mean "to ask" in general contexts. Inquire, is best reserved to mean a "formal" investigation.

So, one might enquire about the adviseability of investing in the telecoms sector but would conduct an inquiry into the Worldcom failure.

Richard English

The usage of "insure" when the person actually means "ensure" is yet another pet peeve of mine. And yes, I do believe it is an Americanism and, while to say this will undoubtedly cause me to be accused of being inconsistent, if a million Americans misuse these words they will all be in error. When someone says that they want to insure my comfort, I always ask if they're going through State Farm or LLoyd's of London.

Time does change the language. For example the perfectly precise word "decimate," meaning to destroy one tenth of something has degenerated to meaning, in very general terms, to get one's butt kicked in a big way. I've given up on that fight.

"Evacuate" is another term widely misused, often to humorous effect to anyone who knows that the term means "to empty out." From the correct usage "Following the disaster, the town was evacuated" the barely correct formulation "50 people were evacuated from the town" sprung. But it was just a short step from this to "50 people were evacuated" which, medically speaking, means that they were all given enemas which, considering the fact that the poor residents have already just suffered a disaster, is probably not the best course of action to take.

Interesting, CJ. I am also irritated about the misuse of "decimate". However, someone once explained to me that if, in war, 1 in 10 were killed, the army would be "decimated"; he said that's how the term evolved. I am not sure if he is correct.
However, I have never thought about "evacuated" in that way, and, of course, you are right. Whenever there is a disaster and "people are evacuated", I will remember you!

quote:

---

However, someone once explained to me that if, in war, 1 in 10 were killed, the army would be "decimated"; he said that's how the term evolved. I am not sure if he is correct.

---

It was a punishment where one in ten of the offenders was put to death.

Yes, Arnie, in the Roman Army they would kill 1 in 10 people in mutinous legions as a punishment. However, would killing 1 in 10 soldiers substantially decrease the size of the unit? That really is what "decimate" has come to mean. In fact, the meaning is really stronger than "substantially decrease"--"obliterate" is probably better.

I just read an article in the Chicago Tribune that says, "Between 7,500 and 8,500 workers-about 1 out of every 10-are leaving..." because Illinois is offering early retirement to save money. However, I can envision the following headline: "Illinois' State Workers are Decimated!"
Another statement said that this early retirement will create a "brain drain" in state government. When one considers the state of affairs in Illinois now, that is worrisome!

Yes, decimate literally means to reduce in size by one tenth. As I said, it was a punishment used by the Romans.

If we accept the metaphoric usage of today - after all no-one but Pol Pot puts his own soldiers to death pour encourager les autres these days - I suppose we must accept the loss of the link with a tenth as well. It is used nowadays for any large reduction.

Personally I don't like its use in modern writing. It is clichéd.

I agree, Arnie, I don't like seeing "decimate" used that way, either.

I had the occasion today to use "ensure" versus "insure" and decided to come to this forum for some direction. I was supposed to send a memo saying that we would "ensure" adequate resources. I wanted to use the correct term, meaning to "make certain" that we have adequate resources. After reading this, lo & behold, I see that I think like the English and not the Americans! I am so impressed with me!

Reviving a very old thread:
We've talked about the British/American differences with ensure/insure a lot on this board, but I am referring to this old thread because it specifically addresses the definitions.

Poor William Safire. In his "On Language" in the NY Times he tells about an OED citation from a 1976 column. However, the lexicographer quickly "wiped the smirk off my face" because of a sic: "W. Safire: 'Program murder boards' have been established to insure [sic] that the concept is structured properly." Safire is quite kind, though, in his conclusion: "You know what? The Brits have a useful distinction; that [sic] should stick. Everybody back up on the ramparts."