Until and till are usually interchangeable, but you should avoid 'til. You might be surprised how recent this error is!
I regularly receive questions from people who are confused about the words until, till and 'til.
When you're talking about a period of time that must lapse before something happens, till and until are equivalent. Don't believe it? Check a dictionary. Some sources say that until sometimes has a more formal sound than till, but often the two words are just interchangeable. Here are two examples:
We spun in circles until we were dizzy.
We ran till we were breathless.
And till isn’t contraction of until either. They’re two separate words, and till actually came first. It’s the older word, first used in the 12th century. People didn’t start using until until the 13th century.
Nearly all the style guides I checked recommended against using ‘til. For example, the American Heritage Dictionary of the English Language says the form is “etymologically incorrect,” the Chicago Manual of Style says it “should not be written ‘til,” and Garner’s Modern English Usage calls it “incorrect” with “no literary history.” In fact, Garner’s says people didn’t really even start thinking ‘til was OK until the 1980s, so it’s a quite recent error.
Many style guides also go out of their way to emphasize that till is fine, which is often a clue that at some point people said it wasn’t; and given that I’ve had to answer questions about disputes over the word, I think that if you want to completely avoid controversy, it's safest to stick with until. But I’ll do my part and say there’s absolutely nothing wrong with till.
One final interesting thing is the etymology of till. We’ve been talking about the preposition and conjunction, but of course, it’s also a verb that means “to work dirt” (as in to till the land) and a noun that means “a box or drawer that holds money” (as in put the money in the cash register till).
You might think these words all came from the same place since they’re all spelled the same, but they don’t. According to The Online Etymology Dictionary, all three have completely different origins.
So that’s your Quick and Dirty Tip: Until and till are essentially interchangeable. If you want to be super safe, stick with until and definitely avoid ‘til.
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