Surprisingly few studies have explored the intuitive connection between self-control and weight loss. We tracked participants’ diet, exercise and weight loss during a 12-week weight loss program. Participants higher in self-control weighed less and reported exercising more than their lower self-control counterparts at baseline. Independent of baseline differences, individuals high in dispositional self-control ate fewer calories overall and fewer calories from fat, burned marginally more calories through exercise, and lost more weight during the program than did those lower in self-control. These data suggest that trait self-control is, indeed, an important predictor of health behaviors.

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We conducted a preregistered multilaboratory project ( k = 36; N = 3,531) to assess the size and robustness of ego-depletion effects using a novel replication method, termed the paradigmatic replication approach. Each laboratory implemented one of two procedures that was intended to manipulate self-control and tested performance on a subsequent measure of self-control. Confirmatory tests found a nonsignificant result ( d = 0.06). Confirmatory Bayesian meta-analyses using an informed-prior hypothesis (δ = 0.30, SD = 0.15) found that the data were 4 times more likely under the null than the alternative hypothesis. Hence, preregistered analyses did not find evidence for a depletion effect. Exploratory analyses on the full sample (i.e., ignoring exclusion criteria) found a statistically significant effect ( d = 0.08); Bayesian analyses showed that the data were about equally likely under the null and informed-prior hypotheses. Exploratory moderator tests suggested that the depletion effect was larger for participants who reported more fatigue but was not moderated by trait self-control, willpower beliefs, or action orientation.

Free will can be understood as a novel form of action control that evolved to meet the escalating demands of human social life, including moral action and pursuit of enlightened self-interest in a cultural context. That understanding is conducive to scientific research, which is reviewed here in support of four hypotheses. First, laypersons tend to believe in free will. Second, that belief has behavioral consequences, including increases in socially and culturally desirable acts. Third, laypersons can reliably distinguish free actions from less free ones. Fourth, actions judged as free emerge from a distinctive set of inner processes, all of which share a common psychological and physiological signature. These inner processes include self-control, rational choice, planning, and initiative. Do humans have free will? The term and concept have been controversial and the question has long evaded definitive answer, not least because the terms have been used with different meanings and contexts, so that disputants talk past each other. Scientists bridle at the concept of free will as a source of behavior that lies outside of causality. Lawyers and judges alter how they treat someone based on whether the problem behavior was performed freely or not. Moral judgment and guilt depend heavily on estimations of whether the person could have acted differently. Theologians assume that divine judgment of immortal souls depends on whether individuals freely engaged in sin.The authors of this article are experimental social psychologists. We frankly doubt that any experiment or collection of experiments can prove the existence or nonexistence of free will in a way that will satisfy all who use the term. Nevertheless, we think psychology and experimentation can make a useful contribution. In this article, we summarize empirical findings relevant to four hypotheses about free will. First, people tend to believe in free will. Second, that belief has behavioral consequences. (Moreover, these consequences will furnish a promising suggestion as to the social functions of the concept of free will.) Third, people can reliably distinguish between free and unfree actions. Fourth, there are genuine differences in inner processes that produce the free versus unfree actions.Thus, we think that research can show why free will is a useful concept and can establish real phenomena associated with that concept. None of this proves or disproves the metaphysical reality of free will, of course. Rather, the contribution of psychology would be to say that if free will is genuine, then this is how it works, and if it is illusory, then this is the reality that is often mistaken for it.