The notion of capacity implicit in the Mental Capacity Act is subject to a tension between two claims. On the one hand, capacity is assessed relative to a particular decision. It is the capacity to make one kind of judgement, specifically, rather than another. So one can have capacity in one area whilst not having it in another. On the other hand, capacity is supposed to be independent of the ‘wisdom’ or otherwise of the decision made. (‘A person is not to be treated as unable to make a decision merely because he makes an unwise decision.’ [Department of Constitutional Affairs 2005: section 1].) One may have capacity even if the decision one arrives at is seen as unwise by one’s doctor. In this short note I will explore this tension. By saying that there is a tension between these two claims, I do not mean that they are inconsistent. They can both be true. But there is a natural way of thinking about the first claim, suggested by the second, which is false and accommodating both in its absence puts limits on just how atomic or decision specific capacity can be.