The Theory of Planned Behavior

The theory of planned behavior formulated by Ajzen (1991) has become one of the best-known theories in psychology. Roughly, it states that behavior depends on the intention or resolve of the individual to behave in a certain way, say, to exercise at least five times a week. Intention itself depends on a behavioral attitude (e.g., exercising at least five times a week would be good/bad), subjective norms (e.g., most people important to the person think that she or he should exercise at least five times a week), and perceived behavioral control (e.g., exercising at least five times a week would be easy/difficult). This theory, in its new versions, is referred to as the “reasoned action approach” (Fishbein & Ajzen, 2010).

As depicted in Fig. 6.1, action depends on previous knowledge in the form of intention. The empirical evidence bearing out this theory is impressive, with metaanalyses of empirical studies (Armitage & Conner, 2001; Manning, 2009) overwhelmingly showing a strong connection between intention and subsequent

The main elements that constitute the theory of reasoned action

Fig. 6.1 The main elements that constitute the theory of reasoned action. Behavioral attitude, subjective norms, and perceived behavioral control causes intention that brings about behavior (with additional influence from perceived behavioral control) behavior. But is this finding really a surprise? Werner Greve, a psychologist from Hildesheim University, has argued that the empirical success of the theory of planned behavior is not astonishing. According to him, the connection between intention and action is logical, not causal. In his article “Traps and Gaps in Action Explanation” (2001), he stated that intention is an inherent part of what is called action. Speaking about action therefore implies the assumption that an intention must exist to carry out a certain action.

The consequence of Greve’s (2001) argument is clear. In his view most of the empirical studies on the theory of planned action are pseudoempirical research in that things that are true a priori are proven empirically. If a person intends to diet and sometime later starts to undergo dietary treatment, that action comes as no surprise. It is a logical consequence of the fact that at some time t a person decides to begin dietary treatment and then at time t + 1 the diet really commences. But what about the cases in which persons do not start their dietary treatment? Would their lapse falsify the logical connection between intention and action? No, it would only mean that the intention was not strong enough to reach a threshold needed to turn intention into behavior.

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