For five centuries, a font was not a file but an inventory. It was a physical thing you could weigh and run short of: one small metal block for every letter, and a separate block for each size and each style. A single typeface, held in one size, was a drawerful of tiny castings, and to set a page a compositor drew them out one by one and lined them up by hand. The word font carried the sense of a supply, a quantity of metal, because that is precisely what it was.

The way that metal was stored has quietly shaped how we speak. Compositors kept their letters in two wooden cases stacked before them. The capitals lived in the upper case, further from the hand and used less often; the small letters lived in the lower case, near at hand for the constant work of ordinary words. From that simple arrangement, upper and lower, comes the entire etymology of uppercase and lowercase. Every time we name the two forms of a letter, we are describing where a printer once reached to find it.

One more trace survives in an unlikely place. Between the lines of set type, compositors slipped thin strips of spacing metal to hold the rows apart, and those strips were cast from lead. The practice named itself after the material: adding space between lines was called leading. Centuries later, when typographers moved onto screens and there was no metal left anywhere in the process, the word came along anyway. Cascading Style Sheets, the language that lays out nearly every page on the web, still sets what it calls leading, spacing lines of light with a term inherited from strips of lead. It is a fine example of how the old craft embedded itself so deeply in the vocabulary that we keep using its words without noticing the metal they came from.