Laws of UX
Law of Similarity
Things that look alike are assumed to behave alike — appearance reads as meaning.
Where it comes from
It's another of the Gestalt principles from early-twentieth-century perceptual psychology. Where proximity groups by position, similarity groups by appearance: the mind assumes that things sharing a colour, shape, or style belong together — and behave alike.
Why it matters for your website
The eye reads appearance as meaning. The Law of Similarity says people assume things that look alike work alike. When interactive and decorative elements are visually indistinguishable, users don't know what to click — and hesitation kills action.
On the web this has a sharp, practical edge: appearance is a promise about behaviour. If your links are blue and underlined, then anything else blue and underlined will be taken for a link — and anything that is a link but isn't styled that way will be missed. Consistency of appearance isn't decoration; it's how the interface tells users what they can do.
The failure mode runs both ways. Style something non-interactive to look like a button and people will click it in vain; style a real control to look like plain text and they'll never try it. Every visual style you use is teaching the user a rule, and they will apply that rule everywhere they see it.
Wrong vs right
Decorative elements styled like buttons (rounded, filled, coloured) that aren't clickable, so users click them and nothing happens.
A consistent visual language where one specific style means 'clickable' and nothing else borrows it.
Real links that look like ordinary body text, so users never realise they can be clicked.
All interactive text sharing the same recognisable treatment, so what's clickable is obvious at a glance.
Mixing several unrelated button styles for the same kind of action, so the eye can't tell which controls are equivalent.
Equivalent actions sharing one style, so similarity signals 'these do the same kind of thing'.
Understanding Law of Similarity
The Law of Similarity is the Gestalt principle that elements sharing visual characteristics — colour, shape, size, style — are perceived as related, even when they're far apart. The eye reads alikeness as kinship: similar things are assumed to be of the same type, with the same role, and the same behaviour. It's how a user can glance at a page and instantly tell the links from the headings from the buttons.
For interface design, the most important application is that similarity governs perceived interactivity. Users learn the visual signature of the things they can act on — the colour of links, the shape of buttons — and then apply that learning across the whole product. This makes consistency a functional requirement, not a stylistic nicety: the same kind of element must look the same everywhere, and different kinds must look different.
The corollary is a discipline about not borrowing styles. The moment a non-interactive element copies the look of an interactive one, you've made a false promise the user will act on. Reserving interactive styles for genuinely interactive things — and keeping decorative elements visibly distinct — is what keeps a page honest about what it can do. It connects directly to consistency and to the law of proximity.
How Kweri checks it
Kweri can catch some concrete similarity problems — for instance interactive and non-interactive elements that share a confusingly similar style, or inconsistent treatment of the same kind of control. But judging whether two things are 'similar enough' to be confused, and whether that confusion matters in context, often needs a human read. So Kweri flags likely cases where appearance and behaviour are out of step, and treats the finer calls as prompts for your judgement rather than hard failures.
FAQ
What is the Law of Similarity?
The Law of Similarity is a Gestalt principle stating that elements which look alike — in colour, shape, size or style — are perceived as related and assumed to behave alike. It's how users tell links, buttons and headings apart at a glance.
How does the Law of Similarity affect usability?
Strongly, because users treat appearance as a signal of behaviour. If something looks like a link or button, they'll expect it to act like one. Consistent styling of interactive elements tells users what they can click; inconsistent styling causes hesitation and mis-clicks.
Why shouldn't decorative elements look like buttons?
Because similarity implies shared behaviour. If a non-interactive element looks like a button, users will click it and be frustrated when nothing happens. Reserve interactive styles for things that are genuinely interactive.
How is similarity different from proximity?
Proximity groups elements by how close they are; similarity groups them by how alike they look. Similarity can group items across a whole page regardless of distance — all the blue underlined words read as links wherever they appear.
What does the Law of Similarity mean for consistency?
It makes consistency functional, not just aesthetic. The same kind of element should look the same throughout, and different kinds should look clearly different, so users can reliably predict behaviour from appearance.
Related principles
Things placed close together are seen as related; things spaced apart are seen as separate.
Follow platform conventions and stay internally consistent so the same thing always means the same thing.
The eye separates a subject (figure) from its surroundings (ground) — that separation must be unambiguous.
Attribution & sources
Identified by Gestalt psychologists (incl. Max Wertheimer) (1920s). Catalogued from Laws of UX (Jon Yablonski).
One of the Gestalt principles of perception; popularised for designers by Jon Yablonski's Laws of UX.
See Law of Similarity on your own site
Run a free Kweri audit — a plain-English review of your site’s speed, accessibility, SEO and design, ranked by what to fix first. No login, no jargon.
Run a free audit →