This paper considers the interpretation of section 25(2)(c) of the Mental Capacity Act 2005, on the relevance of subsequent inconsistent behaviour by the maker of an advance decision. Consideration of the very few cases, and analysis of how existing rules of statutory interpretation could be applied, identifies a particular problem in relation to those who appear to contradict their own prior decision, but do so after they have lost capacity. This highlights an issue which has already been raised in the philosophical literature where there has been some discussion of the relevance and moral authority of our own prior decisions over our future selves, particularly where our future self appears content with a situation which would have been intolerable to our prior self. The incidence of cases of this type is not confined to the realms of philosophy; indeed these kinds of situations are likely to increase, given predictions of the rise in cases of dementia over the next 30 years, and so we will require an unambiguous legal framework to deal with assessing the validity of an individual’s advance decision, and the ramifications of acting upon it. The law, as currently stated, is not clear in respect of these types of cases, and should be revised to provide clarity, and with it the greater confidence and uptake in advance planning desired by central government.