Theory of Planned Behaviour (Ajzen)

The Theory of Planned Behaviour (TPB) is a social-psychological model formulated by Icek Ajzen in 1985 in his chapter "From Intentions to Actions: A Theory of Planned Behavior," and developed fully in his 1991 paper of the same name published in Organizational Behavior and Human Decision Processes. It is a direct extension of the Theory of Reasoned Action (TRA), which Ajzen had co-developed with Martin Fishbein in 1975 and 1980. The TRA held that volitional behaviour could be predicted from behavioural intention, itself a function of attitude and subjective norm. Ajzen added a third determinant—perceived behavioural control—to account for behaviours that are not entirely under a person's voluntary command, thereby widening the model's explanatory range. The theory belongs to the family of expectancy-value models and is among the most cited frameworks in social psychology, public health, and, in the Indian civil-services context, the UPSC General Studies Paper IV (Ethics, Integrity and Aptitude) syllabus segment on attitude.

The model's central mechanism proceeds in an ordered chain. The most proximal cause of a behaviour is behavioural intention—the conscious plan or motivation to perform an act. Intention, in turn, is determined by three independent antecedents. The first is attitude toward the behaviour, the degree to which a person holds a favourable or unfavourable evaluation of performing it, derived from behavioural beliefs about likely outcomes weighted by the value placed on those outcomes. The second is the subjective norm, the perceived social pressure to perform or not perform the behaviour, formed from normative beliefs about what significant others expect, weighted by the motivation to comply. The third is perceived behavioural control, the person's sense of how easy or difficult the behaviour will be, reflecting both internal capacity and external opportunity. The stronger the favourable attitude, the supportive norm, and the perceived control, the stronger the intention—and the more likely the behaviour.

A distinguishing feature of the TPB is that perceived behavioural control operates along two pathways. It influences behaviour indirectly through intention, but it can also predict behaviour directly, because perceived control often serves as a proxy for actual control over resources and skills. Ajzen drew on Albert Bandura's concept of self-efficacy in conceptualising this construct, and the two ideas overlap substantially. The theory assumes that each determinant rests on accessible salient beliefs, and that the relative weight of attitude, norm, and control varies across behaviours and populations—for some acts social pressure dominates, for others personal evaluation or felt capability does. Later refinements, including Ajzen and Fishbein's 2010 Reasoned Action Approach, incorporated background factors such as demographics, knowledge, and personality as distal influences operating through the three core constructs.

The TPB has anchored decades of applied research. Public-health ministries and agencies—including programmes informed by the World Health Organization and national bodies such as Public Health England before its 2021 dissolution—have used it to design interventions on smoking cessation, condom use, vaccination uptake, and dietary change. During the COVID-19 pandemic, researchers across capitals from London to New Delhi applied TPB constructs to model mask-wearing and vaccine intention through 2020 and 2021. In environmental policy, the framework underpins studies of recycling and energy conservation behaviour. Within India, the model appears regularly in UPSC ethics preparation as the canonical account of how attitudes translate into administrative conduct, and it informs nudge-style governance thinking associated with bodies such as NITI Aayog.

The TPB must be distinguished from its neighbours. Against the Theory of Reasoned Action, the TPB adds perceived behavioural control and therefore applies to non-volitional behaviours that TRA cannot handle. It differs from the Health Belief Model, which emphasises perceived susceptibility, severity, benefits, and barriers rather than social norms and intention. It is narrower than the Transtheoretical (Stages of Change) Model, which is processual and stage-based rather than a single predictive equation. It also differs from pure nudge theory and behavioural-economics accounts, which stress automatic, non-deliberative System 1 processes; the TPB is a deliberative, reasoned model that assumes conscious cognitive weighing.

The theory has attracted sustained criticism. Its strongest documented weakness is the intention-behaviour gap: meta-analyses, including Sheeran's 2002 review, find that intentions explain a substantial share of variance in intention but a markedly smaller share of actual behaviour, because good intentions frequently fail to convert into action. Critics including Falko Sniehotta and colleagues called in a 2014 paper for the theory to be "retired," arguing it neglects emotion, habit, impulsivity, and unconscious determinants. Ajzen has responded that the model never claimed to be exhaustive and that habit and affect operate through the existing constructs. Subsequent extensions add anticipated regret, moral norms, self-identity, and implementation intentions to close the gap.

For the working practitioner—whether a policy desk officer designing a public-compliance campaign or a civil-services aspirant reasoning through a GS4 case study—the TPB offers a disciplined diagnostic. It directs the analyst to ask which of three levers is binding: do citizens hold an unfavourable attitude, perceive contrary social pressure, or believe they lack the capacity to act? Each diagnosis implies a different intervention—information and framing for attitude, peer and leadership endorsement for norms, and skills, resources, or procedural simplification for perceived control. Its enduring value lies in converting the vague injunction to "change behaviour" into specifiable, measurable, and separately addressable causes, which is precisely the analytical move expected of an effective administrator.