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constrain

/kənˈstreɪn//kənˈstreɪn/·verb
to limit something's freedom of action, movement, or growth
Fig. 1 — The kite flies like it means it — loops, dives, climbs — and three times it makes a real run for the open sky.
01Definition

To constrain is to draw the boundaries something must live inside: Latin constringere, 'to bind together'. Budgets constrain designs, treaties constrain governments, gravity constrains everything with mass. The force is usually quiet and structural rather than violent — what is constrained still acts, still grows, but only within the limits imposed, which is why the passive is the word's natural habitat: constrained by time, constrained by convention. The noun constraint names each individual limit, and engineering and mathematics use both with complete precision.

02In use
  • iThe old bridge's width constrains how much traffic the whole valley can carry.
  • iiGrowth in the region is constrained less by talent than by housing.
  • iiiThe kite can climb as fast as it likes; the string constrains only its range.
03Collocations
  • constrained by
  • severely constrain
  • budget constraints
  • constrain growth
  • time constraints

Family constraint (noun) · constrained (adjective)

04Relations

=restrict, limit, curb, confine, inhibit

≠liberate, free, unleash

05Compared
PairThe difference
constrain vs constraintneed a verb, something limiting something → constrain; need a noun, the limit itself → constraint.
constrain vs constrictan outside limit on what something may do → constrain; a physical squeeze making something narrower → constrict.
06TOEFL & IELTS

Cornerstone academic vocabulary: TOEFL passages constrain everything from gene expression to monetary policy, and 'constrained by' is one of the most reusable passives in Writing Task 2 — 'policy options are constrained by public debt'. Distinguish the family: constrain sets limits from outside, restrain holds a thing back from acting at all, restrict narrows what is allowed. The noun constraint is equally exam-ready: work within constraints, a binding constraint.

07Asked
What is the difference between constrain and restrain?
Constrain limits scope; restrain stops action. A budget constrains a project — it continues, inside limits. A guard restrains a suspect — the action is prevented bodily, now. Constrain is structural and often abstract; restrain is physical and immediate, which is why you restrain a dog but are constrained by regulations. If the limit is a fence around options, constrain; if it is a grip on an arm, restrain.
What is the difference between constraint and restraint?
Constraint is the limit imposed on you: time constraints, budget constraints, a design constraint. Restraint is either the physical device that holds (a child restraint) or the self-control you exercise — 'he showed admirable restraint'. The tell: constraints come from outside and are worked within; restraint, in its most prized sense, comes from inside and is shown.
What does 'constrained by' mean?
Limited by — the passive frame the word likes best: constrained by cost, by geography, by the data available. It reports that an actor still acts, but inside boundaries set elsewhere, with no blame attached. Academic prose leans on it precisely because it is neutral: 'the study was constrained by sample size' concedes a limit without confessing a mistake.
Is constrain the verb form of constraint?
Yes — constrain is the verb, constraint the noun: you are constrained (verb) by constraints (noun), and the noun ends in -t. The full word-class drill, with both animated scenes, is on the constrain vs constraint page linked in the 'Compared' list above.
What is the difference between constrain and constrict?
Constrain draws the boundary; constrict physically squeezes. Rules constrain behaviour but never tighten around anything; a snake or a narrowing artery constricts, making the space itself smaller. In the scene above, the string never squeezes the kite — it flies as hard as ever; the string only decides its range. If the space itself tightens, constrict; if only the options do, constrain.
Can people be constrained, or only things?
People, constantly — but by circumstances rather than hands: researchers constrained by funding, artists constrained by convention, ministers constrained by coalition partners. Applied to people the verb keeps its impersonal dignity; it describes the box, not a scuffle. When the limiting force gets physical, English switches verbs — the crowd was restrained — which is exactly the constrain/restrain line examiners like to see held.