As you probably already know, collared shirts with buttons running down the middle are typically referred to as either button-ups or button-downs. Some people have a strong preference for one term over the other; others use them interchangeably, believing (erroneously) that they’re synonymous.

Last November, model and author Chrissy Teigen took to Twitter and asked in a poll, “Is it a button up or button down?” Of the 220,000-plus respondents, 66 percent said button-up, and 34 percent said button-down. On the other hand, button-down appears to be the more searched-for term overall, according to Google Trends.

So which one is right? As it turns out, the two terms actually refer to two different garments. The button-down shirt came to be in the late 1800s, thanks to British polo players. Their uniform typically consisted of flannel pants, a wool sweater, and a long-sleeve shirt—all in white. It looked pretty snappy, but the players quickly became irritated by their collars flapping in the wind as they rode around on their horses.

According to Charles Panati’s book on the Extraordinary Origins of Everyday Things, “Players routinely asked seamstresses to batten down their collars, and two buttons became the most popular solution to the problem.” This was called a polo collar at the time, and the style was soon popularized by John Brooks, whose father founded the Brooks Brothers clothing line. (Oddly, polo shirts as we know them today were actually made for tennis, not polo.)

This is all to say that button-down shirts have buttons attached to the collar, while button-up shirts do not. Here’s where it gets a little confusing, though: All shirts with buttons can be called button-ups. However, only some button-ups (the ones with buttons on the collars) can be called button-downs.

A man wearing a button-down shirt iStock.com/azndc

As Megan Collins of Style Girlfriend explained it to the Today show, it’s kind of like how “an apple is a fruit, but not all fruits are apples.”

If you ever get mixed up, just keep in mind that the collars of a button-down can be buttoned down. As for their sartorial differences, button-down shirts are less common these days, especially among women's styles. They also tend to be slightly more casual than shirts with free-flapping collars, according to Collins.

If ties aren't your thing, but you're still trying to win style points, you should stick with the more versatile button-up shirt, according to Mainline Menswear.

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