Think for even a fleeting moment about the expression of course and you’ll probably start to have questions. Is it a course of action, a course of study, or some other kind of course? Why is there a preposition in front of it? How did the phrase come to connote an emphatic “Yes!” in the first place?

It all started with the Latin noun cursus, which the Oxford English Dictionary defines as the “action of running,” a “path taken or to be followed,” and a “method of proceeding,” among other meanings. Those didn’t change much as the term passed into other languages, including French (cours) and English (course).

As early as the 13th century, the Anglo-Normans were using de cours to signify when something was routine, and English speakers started doing the same with of course in the 1500s. The expression was basically a concise way of conveying that something had followed or would follow the normal course of things; i.e., it was exactly how you’d expect it to be. By the late 1700s, of course had taken on an even more concentrated version of that meaning: “naturally” or “obviously.”

The earliest known instance of this latter sense comes from a letter that English writer Charlotte Smith sent to her publisher, Thomas Cadell Sr., in 1790. In it, she tells him she’ll need a few extra weeks to finish her latest manuscripts for two reasons: She’s “straining every nerve” trying to secure her daughter’s betrothal to a wealthy suitor and therefore “of course work[s] more slowly” due to the lack of alone time; and she is “of course very unwilling to risk” her “increasing reputation” as a writer by rushing to submit subpar work.

Within just a few decades, people had made the leap from using of course as a qualifier meaning “naturally” or “obviously” to using it as an affirmative answer that worked wherever one of those terms could also work. How the expression has managed to remain pretty common throughout all these years is anyone’s guess. Maybe its staying power is related to its versatility: Depending on the context, of course can express condescension (as in “Duh!”), realization (like “Eureka!” in a light bulb moment), enthusiasm (e.g. in reply to “Will you marry me?”), and much more. That, and it rolls off the tongue a little better than, say, “Such is the normal course of events!”

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This article was originally published on www.mentalfloss.com as Why Does ‘Of Course’ Mean ‘Yes’?.