Parentheses, square brackets, and curly braces are the only punctuation marks that always come in pairs. Each one has to open, hold something, and close, which makes them some of the most structurally demanding glyphs in a typeface. They’re also the source of one of the stranger word origins in English.

A Short History of Parentheses and Brackets

The word “parenthesis” comes from the Greek parenthesis, meaning “putting in beside.” In ancient Greek and Latin, it described an aside inserted into a sentence, not the marks that surround it. Early writers had no dedicated mark for it, and used commas or dashes instead.

The curved marks appeared in medieval Italy. In the 14th century, humanist scholars, with the writer Coluccio Salutati usually credited as an early champion, began using curved marks to enclose asides, and these were sometimes called lunulae, Latin for “little moons.” The shape caught on with early printers and spread across Europe.

Square brackets have a more architectural story. The English word “bracket” first meant a support that holds up a shelf or beam, and it traces back through French to a word for a codpiece. Printers started using the name for the square marks in the 18th century, probably because of the way the mark’s shape looked like a supporting corner.

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Curly braces came later and became most closely associated with music and mathematics. In sheet music they join staves together, and in math they group sets. Programming languages later adopted them as one of their main tools.

Anatomy of Parentheses and Brackets

All three pairs share a structure: an opening mark that faces the text it will hold, and a closing mark that faces back. They are mirror images of each other, but in a good typeface they aren’t exact reflections.

Parentheses are curved. They bow outward, thick in the middle and thin at the tips, echoing the contrast of a pen stroke. They usually extend from above the ascender line to below the descender line, so they can wrap around tall letters like “l” and descenders like “p.”

Square brackets are straight. They’re built from a vertical bar with short horizontal ticks at the top and bottom, like a squared-off version of the parentheses.

Curly braces are the most complex. Each one is made of two opposing curves meeting at a sharp central point, like a pair of back-to-back S shapes. Because the curves have to be symmetrical and the point has to be crisp, braces are among the hardest glyphs in a typeface to draw.

Angle brackets (< >) are also used, especially in code and markup languages. They’re often drawn as simple diagonal pairs and sometimes get confused with the “less than” and “greater than” signs, which are different glyphs.

Designing Parentheses and Brackets From Scratch

The biggest design challenge is vertical extent. If the marks are too short, they crash into ascenders and descenders. If they’re too tall, they look like they’re floating above the text. Designers typically extend them slightly past the tallest and lowest letters, then check them against a range of words.

Spacing is the second challenge. An opening mark needs a tight space on its right and a bit more room on its left. A closing mark does the opposite. Because the two marks mirror each other, designers adjust each side separately to account for the letters that will sit next to them.

One well-known problem is the lowercase “f.” In many typefaces, the hooked top of an italic or old-style “f” can collide with an opening parenthesis in a sequence like “(f.” Designers spend time kerning or redrawing to prevent this.

Capitals bring another issue. Parentheses are usually centered around the height of lowercase letters, which can make them look low next to all-caps text. Many fonts offer a “case” feature in OpenType that raises the marks so they center correctly around capitals and numerals.

Unique Facts About Parentheses and Brackets

In programming, these marks work almost like punctuation with different jobs. Parentheses group expressions and call functions, square brackets create lists and index items, and curly braces define blocks of code or objects. Lisp, an old programming language, is so full of parentheses that its name has been joked about as meaning “Lots of Irritating Superfluous Parentheses.”

Square brackets have a special role in writing: they mark added words inside a quotation, like “she said [that] it was fine,” so readers know the quoted text has been altered.

In math, the different types of brackets often carry meaning. In some notations, a square bracket means that an endpoint is included in a range, and a parenthesis means it’s excluded.

Parentheses and Brackets in Popular Fonts

In Garamond and other old-style serifs, parentheses have visible stroke contrast, thickest in the middle and tapering at the ends, echoing a broad-nib pen. Helvetica uses more even strokes and a rounder, simpler shape, matching its neutral character. Futura keeps parentheses slender and nearly geometric.

In script and handwriting fonts, these marks are often slightly uneven and slanted, so they look like they were drawn in a single quick motion.

Summary

Parentheses began as a grammar term for an inserted aside, took their shape from medieval Italian scholars, and gave us a family of paired marks used in writing, music, math, and code. Their design challenge is balance: they have to wrap around every kind of letter without colliding with any of them.

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