Topic
Laws & principles
UX treats laws like other fields treat equations - Jakob’s, Tesler’s, Gestalt principles - and designers use them to settle arguments. The problem? A law recalled from memory is easy to misuse; a law you’ve truly felt is one whose boundaries you know.
These are the named rules and rules of thumb that turn up in every critique. Each packs a real observation about people into a phrase short enough to wield - which is exactly why it pays to know what the phrase genuinely claims, and where it stops being true.
So each entry hands you the principle to operate rather than recite: you do the thing, watch the effect land on yourself, and come away able to tell when it applies and when someone is just name-dropping it.
The laws & principles entries 19
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laws & principles
Fitts's law
The time it takes to hit a target grows as the target gets smaller or farther away. Large, close targets are quicker to hit; small, distant ones take longer.
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laws & principles
Hick's law
The more choices you offer, the longer a decision takes - and the cost grows logarithmically, not linearly. Choices take time, not just space.
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laws & principles
Miller's law
Miller's 1956 research showed that our immediate memory for unrelated items is limited - famously 'seven, plus or minus two'. Miller himself cautioned against treating this as a fixed limit, and later studies suggest the number of chunks is often lower, around three to five under controlled conditions. The key insight isn't a magic number: working memory is limited, so grouping information into meaningful chunks helps people retain it.
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laws & principles
Gestalt: proximity
Things close together are perceived as a group; things spaced apart are seen as separate. Proximity is one of the strongest cues for grouping - it usually overrides shape or colour, though a shared boundary or visible connection can override it.
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laws & principles
Jakob's law
People spend most of their time on other sites, so they expect yours to work like those. Familiar patterns are quicker to use because users already know them - you’re reusing the habits the web has taught them.
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laws & principles
Tesler's law
Every process has a minimum complexity that can't be eliminated - only shifted. The real question isn't whether to remove it, but who carries it: the user or the team building it. You can see this in action on this page.
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laws & principles
Weber's law
Weber's law states that the smallest change we can notice in something is proportional to its starting size, not a fixed amount. A £1 rise on a £3 coffee is glaring; the same £1 on a £900 laptop is invisible. The "just-noticeable difference" scales with the baseline, so big things have to change by a lot before anyone perceives it.
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laws & principles
Aesthetic-usability effect
The aesthetic-usability effect is our habit of judging better-looking things as easier to use - whether or not they actually are. Polish buys a benefit of the doubt, smoothing over small frictions and making people more forgiving.
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laws & principles
Pareto principle
The Pareto principle suggests that roughly 80% of effects come from about 20% of causes - the 'vital few'. In UX, this often means a small set of features, flows, or fixes delivers most of the value. The exact split varies and it’s not a precise law; treat it as a prompt to find and prioritise the high-impact minority, not a formula. You can see this in action on this page.
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laws & principles
Postel's law
Postel's law, also known as the robustness principle, suggests being conservative in what you send and liberal in what you accept. This means accepting harmless variations - such as spacing, brackets, or case - while validating, normalising, and storing a canonical version. It does not mean accepting ambiguous, unsafe, or semantically invalid input just for tolerance.
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laws & principles
Parkinson's law
Parkinson's law: work expands to fill the time given. Give it a week and it takes a week; give it an afternoon and it’s done by tea - often just as well.
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laws & principles
Occam's razor
Occam's razor: among designs that solve the problem, the simplest one wins. Avoid adding elements - options, steps, decoration - beyond what’s needed; every extra is one more thing to read, maintain, and get wrong.
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laws & principles
Gestalt: similarity
The Gestalt law of similarity shows how we mentally group items that share visual traits - like colour, shape, or size - and perceive them as belonging together, even when spaced apart. Similarity alone suggests they form a set.
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laws & principles
Gestalt: closure
Closure is the mind’s tendency to complete shapes from partial visual cues - perceiving a whole circle, triangle, or icon even when only fragments are shown.
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laws & principles
Gestalt: continuity
Continuity is how the eye naturally follows smooth, unbroken paths. When lines or rows of elements intersect or branch, group those that continue in the same direction, not those that merely connect.
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laws & principles
Gestalt: common region
Common region is the grouping effect where elements within the same bounded space - such as a panel or tinted background - are perceived as a group, even if other items are closer. It’s one of the strongest grouping cues and typically overrides proximity and similarity. (Grouping via an explicit connector - such as a line joining items - is a related but distinct cue, uniform connectedness.)
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laws & principles
Gestalt: prägnanz
Prägnanz - the law of good figure - means the mind naturally prefers the simplest, most stable interpretation of what it sees. When faced with ambiguity, you perceive the cleanest version: a few whole shapes rather than many fragmented ones. You can see this principle in action on this page.
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laws & principles
Gestalt: uniform connectedness
Uniform connectedness is the grouping effect that happens when elements are visibly joined by a line, bar, or connector - they’re seen as one group even if spaced out or visually different. A clear connection often trumps proximity or similarity. (Grouping by shared enclosure is the related but distinct cue, common region.)
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laws & principles
Gestalt: proximity vs common region
Proximity groups items by how close they are; common region groups them by sharing a boundary or background, and can override spacing.
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Know these already? Take the laws & principles quiz, or revise the terms with flashcards.