Laws of Perception · gestalt
Law of Common Fate
Playable Play this law (~3 min)or keep reading below ↓
Elements that move together are perceived as belonging together. Motion is the strongest grouping cue we have — which is why a menu whose items slide in as one feels like one object, and why scattered, unsynchronised animation feels broken.
Where it comes from
Wertheimer's 1923 papers again: a flock of starlings reads as a single swirling object because hundreds of birds share one motion. Hunters and prey both needed this — synchronized movement means one thing, and the brain groups it before you can blink. Screen animation inherited the rule wholesale: move together, belong together.
Origin: Wertheimer 1923; starling murmurations as the classic demo
In the wild
- Dropdown menus
All the options animate in as one sheet, so twelve links read as one menu, not twelve arrivals.
- Drag interactions
Drag an email thread and every message in it moves as a block — the motion states the grouping.
- Parallax scrolling
Layers moving at different speeds separate foreground from background without a single border.
Further reading
Don't just read it — feel it.
Play the 3-minute game and let your own reactions prove the law.
Play the lesson