When two words are just one letter off from each other, it can be hard to tell them apart. It’s even more difficult if their meanings overlap. Take "insure" and "ensure," for instance. Many people don’t know there’s any difference between them at all. They do have different meanings, but if you’ve been using them interchangeably, are you wrong?
What’s the difference between 'insure' and 'ensure'?
It used to be nothing more than a spelling variation until the mid-19th century. Then linguists began to debate whether the two could really be called the same word. Ultimately a distinction was made.
Generally, "to ensure" means to make sure of something. You’d use this version when you want to exercise some control over a situation and guarantee a particular outcome. When you ensure something, you’re talking more about an event or action than an object. It’s more conceptual and involves creating a specific end result.
Meanwhile, "to insure" refers to insurance. It applies to finances and monetary coverage for personal belongings or tangible conditions. This means that only things with physical value can be insured — your house, your car, yourself. It talks about concrete objects as opposed to potential outcomes.
Are these words ever interchangeable?
You might see people using the two verbs in the same context whether it’s technically correct or not. It’s hard to say it’s wrong when language is so versatile and always adapting. After all, "insure" and "ensure" used to be no different than "color" and "colour."
Today, most English language experts agree there is an identifiable distinction, and therefore the two words are no longer interchangeable. Although their definitions are similar — creating assurance of something, whether monetary or in terms of outcome — their applications are separate enough that one doesn’t make sense in place of the other.
The bottom line is, the difference is subtle enough that you may get away with using the wrong word in verbal conversation, but you'll want to ensure you're using correct usage when writing.