How should we define altruism? Our intuitive understanding of an altruistic act is one that is self-consciously undertaken to further another person’s good at some cost to oneself-or at least a willingness to bear such a cost if required. This does not mean that altruists do not gain by their altruism, only that they also tend to pay a price for doing so. (The person who does voluntary work in a charity shop might gain companionship, for example, and the psychic benefits of furthering a good cause). I say ‘self-consciously’ because I find it hard to imagine that a person could be an altruist without understanding that they were being so (a point to which I shall return briefly). The importance of self-consciously borne personal costs suggests one further central feature of altruistic behaviour: that it is impossible to be an altruist without having altruistic motives, without, that is, the desire to help another at some cost to oneself. Motives are central to altruistic behaviour because they are what power people to bear the costs which their altruism entails. It is hard (perhaps impossible) to be altruistic without at least some desire to be so.