A general theory of the relationship between attitudes and behaviour, according to which behaviour is determined by behavioural intentions, and behavioural intentions in turn are determined by attitudes (1) to behaviour and subjective norms (1). An attitude to behaviour is one's evaluation of the goodness or badness of performing the action in question, and a subjective norm is the perceived social pressure arising from one's perception of the extent to which significant others would like one to perform the action. Algebraically, B(f)BI = w1AB + w2SN, where B denotes behaviour, f indicates a function, BI behavioural intention, AB attitude towards the behaviour, and SN subjective norm; w1 and w2 are empirically determined weights representing the relative importance of the attitudinal and normative components. Attitude towards the behaviour (AB) is determined by one's beliefs about the consequences of the behaviour multiplied by the evaluation of each consequence and then summed (see expectancy-value theory). Subjective norm (SN) is a function of one's perception of the preferences of significant others as to whether one should engage in the behaviour. The weights w1 and w2 reflect the relative influence on behavioural intention of attitude towards the behaviour and subjective norm. The theory was formulated by the US psychologist Martin Fishbein (1936–2009) and the Polish-born US psychologist Icek Ajzen (born 1942) and published in their books Belief, Attitude, Intention and Behavior: An Introduction to Theory and Research (1975) and Understanding Attitudes and Predicting Social Behavior (1980). The theory is well supported by research findings, but a limitation of it is that it applies only to behaviour that is predominantly volitional or voluntary, and this limitation was addressed in the later theory of planned behaviour.