Law of Common Fate
Elements that move together are often perceived as part of the same group.
Shared motion suggests shared purpose.
Open a menu and let every item enter together. The items feel like one panel. Give each item a different direction and pace, and the menu feels scattered. The final layout is the same, but the motion changes the relationship.
Origin
Wertheimer called this factor common fate, or uniform destiny, in 1923. In his examples, dots that shifted together could form a new group. Modern reviews still describe shared movement as a cue for perceptual grouping.
Move related elements in the same direction with compatible timing. The shared behavior helps them read as one change instead of several unrelated effects.
A small stagger can preserve the group when direction and behavior remain consistent. Large differences in timing or trajectory can weaken the connection.
Use different motion to show separation. An item leaving a list can move away while the remaining items close the gap together.
Respect reduced-motion preferences. The relationship should remain understandable through position, spacing, labels, or state changes when animation is limited.
Digital systems
Reordering a List
When one item is dragged, the nearby items move together to open a space. Their coordinated response shows that they belong to the same list and are reacting to one action.
Physical signals
A Flock in Flight
Birds flying in the same direction at the same time are seen as a flock. A bird moving away from that path stands apart from the group.
When related elements animate in unrelated ways, the interface sends mixed signals. People see several effects instead of one coordinated change.
Give related elements compatible direction, timing, and easing. Use a different path only when an item is leaving, separating, or changing roles.