Title case

Title case capitalises the words that carry meaning and leaves the joinery alone. Nouns, verbs, adjectives and adverbs go up; the articles (a, an, the), the short conjunctions (and, but, or) and the prepositions stay down, except when one of them lands first or last, where it goes up regardless. That is the whole rule until you reach a preposition of four letters or more, and there the style guides part company: Chicago keeps every preposition lowercase however long it is, while AP raises the ones of four letters and up, so “with” is down in one house and up in the other and no reviewer can settle it from first principles.

The convention survives in interfaces mostly because Apple kept it. Menu titles, menu items, buttons and alert titles on Apple’s platforms use title-style capitalisation, so a Mac application that switches to sentence case reads as foreign next to everything around it. Microsoft went the other way years ago and now writes almost everything in sentence case, which is why a cross-platform product usually has to pick a side rather than inherit one. What no product should do is reach for text-transform: capitalize, which raises every word including the ones the rule exists to keep down, and turns “The Rise and Fall of a Harbour” into something no style guide recognises. Title case is written by hand or not at all.

Against sentence case the difference is tone. Title case reads as formal, deliberate, a little older, which is exactly right on a marketing headline or a menu bar and can feel stuffy on a settings screen that is trying to talk to someone. It is also slower to write consistently, because every label becomes a small judgement call, and inconsistency is more visible here than in any other typographic decision: two adjacent buttons capitalised differently look like a bug. All caps is a third answer and a different tool, since it discards case information rather than distributing it, and belongs on short labels only.

The practical failure is translation. Title case is close to meaningless outside English, so a string prepared this way and sent to a translator comes back sentence cased in French and noun-capitalised in German, and the interface stops matching itself. If a product ships in one language and wants the older, editorial register, title case is a reasonable choice made once and written into the content guide. If it ships in twenty, the case rule should be the one the other nineteen can actually follow.