The TPB emphasizes behavioural intentions as the outcome of a combination of several beliefs.
The theory proposes that intentions should be conceptualized as ‘plans of action in pursuit of behavioural goals’ (Ajzen and Madden 1986) and are a result of the following beliefs:
■ Attitude towards a behaviour, which is composed of either a positive or negative evaluation of a particular behaviour and beliefs about the outcome of the behaviour (e.g. ‘exercising is fun and will improve my health’).
■ Subjective norm, which is composed of the perception of social norms and pressures to perform a behaviour and an evaluation of whether the individual is motivated to comply with this pressure (e.g. ‘people who are important to me will approve if I lose weight and I want their approval’).
■ Perceived behavioural control, which is composed of a belief that the individual can carry out a particular behaviour based upon a consideration of internal control factors (e.g. skills, abilities, information) and external control factors (e.g. obstacles, opportunities), both of which relate to past behaviour.
According to the TPB, these three factors predict behavioural intentions, which are then linked to behaviour. The TPB also states that perceived behavioural control can have a direct effect on behaviour without the mediating effect of behavioural intentions.