Laws & principles quiz

The laws & principles entries in the glossary, in brief. Open any one for the interactive demo behind it.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.)

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.

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.)

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.