The buttonhole is what made close-fitting clothing possible

A garment has to be got on before it can be worn

This is the constraint that governs all clothing design and it’s easy to overlook. A garment must pass over the body, which means either it is large enough at every point to slide over whatever is wider than it, or it opens.

Without a good fastening, the options are limited. Draped clothing wraps and is held with pins, belts or its own weight. Sewn clothing is either loose enough to pull over the head, or laced through pairs of holes, or tied with cords. All of those work and all of them constrain what a garment can be.

Lacing in particular is capable of a very close fit and it’s slow to do, needs both hands and often another person, and it distributes tension in a way that puts strain on the eyelets. It was widely used, and it was never convenient.

Buttons long predate buttonholes

Buttons made of shell, bone, metal and other materials have been found in a great many ancient contexts, and for most of that history they functioned as ornaments, or as toggles passed through a loop of cord, rather than through a worked opening in the cloth itself.

The distinction matters more than it sounds. A loop is a separate component sewn to an edge, and it stretches, wears and limits how close the two edges can be drawn. A worked buttonhole is an opening cut through the cloth and stitched around to stop it fraying, and it sits within the garment rather than beyond its edge.

The functional buttonhole appears in European clothing in the later medieval period, and its spread is associated with a marked change in the shape of clothing: garments that follow the body closely down the front, with rows of small buttons doing the work that lacing had done.

What close fastening allowed

Once an edge could be closed securely at many points along its length, tailoring could shape cloth to the torso and rely on the fastening to hold it there. The fitted doublet and the shaped bodice depend on that, and so, eventually, does the entire lineage of coats and jackets that follows.

It also allowed openings in places that had not been practical, at cuffs, at the neck, along a sleeve, and wherever a limb had to pass through a narrow point and then be closed in again. A great deal of the detail on tailored clothing exists because a small opening could be closed reliably.

The mechanism is worth stating plainly, because it isn’t obvious: a buttonhole transfers load into the body of the cloth rather than to an edge, so it can hold a garment closed against tension without pulling itself apart, provided it is stitched properly and placed on a stable, interfaced layer.

A buttonhole is a structural component

The stitching around a buttonhole is not decoration. It binds the cut edges so they cannot fray, it reinforces the cloth against the tension the button applies, and on a good garment it is worked over a gimp cord that gives the edge body and holds its shape.

A hand-worked buttonhole knots each stitch at the edge, so the row cannot unravel and the finished edge is dense and slightly raised. A machine-worked one uses a lockstitch or chain and is faster by an enormous margin, which is why it is the norm, and it frays sooner at the ends where the strain concentrates.

The end of a buttonhole tells you what it is for. A rounded or keyhole end gives the shank of the button somewhere to sit under load, which is why it appears on coats and jackets, while a plain bar-tacked end suits shirts where the tension is lower.

The ones that no longer fasten anything

Once buttonholes were established as a mark of tailored construction, they began to appear where nothing needed fastening. Sleeve buttons on a jacket are the familiar case, and on most garments they are decoration with the buttonholes stitched shut or merely printed onto the cloth as a shape.

The lapel buttonhole is the most interesting survivor, since it was originally functional on a coat with a collar that could be turned up and closed at the throat. When the lapel was permanently folded back, the buttonhole remained on the fold, without its button, and became a place to put a flower.

These survivals are the reason old fastenings are useful for reading a garment. A detail retained after its purpose has gone is a fossil, and clothing is full of them, which is why an apparently arbitrary feature usually turns out to have been solving a problem that no longer exists.