Ensure vs insure vs assure: which one to use, the Chicago rule, and examples
Ensure means make sure something happens. Insure means cover against financial loss. Assure means tell someone confidently so they stop worrying. The Chicago Manual of Style, as quoted by Dictionary.com, puts it in one line: "We ensure events and insure things." Here is what each word means, examples and how to check your manuscript.
What each word means
- Ensure: make certain an outcome happens. "A second proofread ensures fewer typos in print."
- Insure: protect against loss with insurance. "The publisher insured the shipment of books." To guard against other risks, it is usually followed by against: "We insured against delays by booking the printer early."
- Assure: tell a person something confidently, to remove doubt. "I assured my co-author the deadline was realistic."
Quick test: ensure takes an event or outcome, insure takes a thing or a risk with money attached, and assure takes a person.
Why they get mixed up
Dictionary.com explains that all three come from the Latin sēcūrus, "safe," and that insure began as a spelling variant of ensure and was used that way for hundreds of years. In the mid-1600s insure picked up the financial sense of paying to cover loss, damage or death, and that sense is what sets it apart today. Dictionaries still list insure as another word for ensure, especially in American English, which is why you will see it in print. But editors following Chicago keep them separate.
Examples
| Sentence | Word | Why |
|---|---|---|
| A clear outline will ___ that every chapter has a job. | ensure | Make an outcome certain |
| The author ___ the rare manuscript before shipping it. | insured | Financial protection |
| My editor ___ me the changes were minor. | assured | Told a person confidently |
| Back up your file to ___ you never lose a chapter. | ensure | Make an outcome certain |
| We ___ against a late launch by printing early. | insured | Guarding against a risk, with "against" |
| Can you ___ readers this method works? | assure | Removing a person's doubt |
Examples written by Scribe Media.
Checking your manuscript
Nonfiction, especially business and how-to books, uses "ensure" a lot, and "insure" often slips in where "ensure" is meant. Search your file for "insur" and keep it only where insurance or financial risk is involved. Then search for "ensure" followed by a person ("ensure you that...") and change those to "assure." A copy editor will catch the rest; see what a copy editor does. For more pairs spellcheck misses, see compliment vs complement and principal vs principle.
Start here: search your manuscript for "insur." Unless the sentence is about insurance or money at risk, change it to "ensure."
Common questions
What is the difference between ensure and insure?
Ensure means to make sure something happens: "Proofreading ensures a clean final file." Insure means to protect against financial loss with insurance: "We insured the shipment." In general senses the two were once used interchangeably, but in edited American prose today, insure is kept for insurance and financial risk.
Is it ensure or insure that something happens?
Ensure. When you mean make certain an outcome happens, use ensure: "to ensure the book launches on time."
What does assure mean?
Assure means to tell someone something confidently to remove their doubt: "I assured my editor the chapter would be in by Friday." You assure a person; you ensure an outcome.
Is insure ever correct for make sure?
Dictionaries record insure as a variant of ensure, especially in American English, and insure began as a spelling of ensure. But The Chicago Manual of Style keeps them apart, and most editors will change insure to ensure when it is not about insurance.
Sources: Dictionary.com, Insure vs. Ensure vs. Assure: What's the Difference? (shared Latin root; insure began as a spelling of ensure; insure's financial sense from the mid-1600s; insure against; The Chicago Manual of Style's line "We ensure events and insure things"), and the Dictionary.com and Wiktionary entries for insure (also recorded as another word for ensure, chiefly US), all read November 2, 2026. Examples and guidance were written by Scribe Media. Published by Scribe Media.