A social‑psychological theory proposing that a person's behaviour is primarily predicted by behavioural intention, which is in turn shaped by three proximal determinants: attitude toward the behaviour (beliefs about outcomes and their evaluation), subjective norms (perceived social pressure), and perceived behavioural control (perceived ease or difficulty of performing the behaviour); perceived behavioural control can also exert a direct effect on behaviour where actual control is limited.

Principle

Changing attitudes, perceived norms, or perceived behavioural control will alter intentions and, when sufficient actual control exists, produce corresponding changes in behaviour; perceived control also moderates the strength of the intention→behaviour relationship.

Demonstration

Illustrative scenario — Situation: A hospital seeks to increase hand hygiene among staff. Recognition: staff report positive attitudes but low perceived control due to scarce dispensers and perceive that peers do not prioritise hand hygiene (norms). Action: install additional dispensers (increase actual and perceived control), run peer‑champion campaigns (shift subjective norms), and provide brief feedback (affect attitudes). Consequence: intentions to perform hand hygiene rise and observed compliance increases when practical constraints are removed.

Misapplication

Treating intentions as behaviour or assuming that modifying stated beliefs automatically yields behaviour change without addressing actual control, habits, emotional drivers, or competing incentives; conflating perceived control with objective control.

Consequence

Provides a structured target set for interventions and measurement (attitudes, norms, perceived control, intentions), supporting designs that combine belief‑change with enhancements of behavioural control; however, reliance solely on intention change risks limited impact where intention‑behaviour gaps or structural barriers exist.

Reversal

For automatic, habitual, impulsive, or highly constrained behaviours (e.g., addictions, reflexive actions) the intention construct poorly predicts behaviour, and models emphasising habit, emotion, or structural determinants may be more appropriate.

Boundary

Clearly within: planned, reasoned actions where individuals can form intentions and exercise control (e.g., scheduling exercise, attending screening). Boundary case: behaviours partly planned but strongly habitual or environmentally constrained. Clearly outside: reflexive or biologically driven acts that bypass deliberative intention.

Semantic Tension

Tension between parsimonious, individual‑level cognitive models of action (attitude/norms/control) and ecological or structural models that prioritise environment, policy and social systems; selection affects intervention focus and evaluation metrics.

Synthesis

TPB offers a concise, testable account of how beliefs and perceived control shape intentions and action, making it useful for designing targeted interventions, but it must be complemented by measures and strategies addressing actual control, habits and contextual constraints to close the intention‑behaviour gap.