Design Atlas"Form follows function" comes from American architect Louis Sullivan's 1896 essay "The Tall Office Building Artistically Considered." He was writing about the exterior of skyscrapers, but the phrase went on to become a rallying cry for the Bauhaus and modernist industrial design broadly — the idea that ornament shouldn't be applied on top of a form; the form itself should be a direct result of what the object does.
Set a Victorian chair next to a modern ergonomic one and the difference is obvious. The ornamental chair adds carved curves to its legs and back as applied beauty, unrelated to how a body actually sits in it. The functionalist chair's backrest curve follows the spine's natural S-shape, and its seat pan angles down at the front edge to relieve pressure behind the knees — every curve in the form is doing a specific job.
Taken to an extreme, the principle hardens into "ornament is a crime," and mid-to-late-20th-century design criticism pushed back hard on that oversimplification — form and function, the argument goes, are always tangled up with culture, emotion, and free will too. Still, as a practical checklist — "why does this curve exist?" — it holds up. Asking whether a shadow or a corner radius in a UI actually signals hierarchy or clickability, or is just there because it looks nice, is the same question in its digital form.
When to use
When checking whether a detail added to a form is actually doing something, or is just decoration.