03 · Seeing
Law of Similarity
People see things that look alike as one group, even when they sit apart.
Evidence: Holds upWhat we do with it
- 01
Give each kind of thing one look and keep it. If buttons come in five styles, people have to learn five things.
- 02
Don't style a plain label like a button. People will try to click it.
- 03
Tie a set together with one color, shape or size, and break the pattern only on purpose.
Examples
Getting it wrong, getting it right.
Don't
The brand red marks links, error messages and decorative headings alike. People click the headings and skim past the errors.
Do
One color means one thing. Links share one style, errors another, and decoration borrows neither.
The evidence
What the research says.
Grouping by color, shape and size has been shown again and again in the lab since the 1920s. The cues aren't equal. In Philip Quinlan and Richard Wilton's 1998 experiments, shared color grouped items strongly and shared shape only weakly, though either could beat closeness under the right conditions.
Sources
- Wertheimer, M. (1923). Untersuchungen zur Lehre von der Gestalt II. Psychologische Forschung, 4.
- Quinlan, P. T., & Wilton, R. N. (1998). Grouping by proximity or similarity? Competition between the Gestalt principles in vision. Perception, 27(4).
- Wagemans, J., Elder, J. H., Kubovy, M., Palmer, S. E., Peterson, M. A., Singh, M., & von der Heydt, R. (2012). A century of Gestalt psychology in visual perception: I. Perceptual grouping and figure-ground organization. Psychological Bulletin, 138(6).
Last reviewed November 7, 2026. How we keep this current