Gestalt Principles
A set of observations from perceptual psychology describing how the visual system groups separate elements into wholes.
In depth
The principles — proximity, similarity, continuity, closure, common fate and figure-ground — explain why compositional devices work at all. They describe automatic, pre-conscious processing, which is why an arrangement that violates them feels wrong before a viewer can articulate any reason.
Examples in practice
Five scattered birds read as a flock rather than five individuals because proximity and similarity group them automatically.