This article investigates the ability of mental incapacity tests to account for problems of control, through a study of the approach to alcohol dependence and a comparison with the approach to anorexia nervosa, in England and Wales. The focus is on two areas of law where questions of legal and mental capacity arise for people who are alcohol dependent: decisions about treatment for alcohol dependence and diminished responsibility for a killing. The mental incapacity tests used in these legal contexts are (...) importantly different—one involves a ‘cognitive’ test, while the other includes an explicit impaired-control limb—and the comparison provides insight into a longstanding debate about the virtues of one type of test over the other. It is shown that both kinds of test can take control problems into account, but also that both can be interpreted in narrow and wide ways that significantly influence the outcome of the assessment. It is therefore argued that to a large extent, it is not the kind of mental incapacity test that matters, but how the test is interpreted. It is further proposed that value judgements are playing an unrecognised and inappropriate role in shaping this interpretation. This raises concerns about the current approach to assessing the impact of alcohol dependency on the capacity to make decisions about alcohol use or treatment, as well as broader concerns about flexibility within incapacity tests. (shrink)