A recurrent problem for moral philosophy, one that we have encountered several times already, is the question of how to bridge the gap between what is the case and what ought to be the case. As we saw in an earlier chapter, philosophical egoists think that in the case of the first person no problem exists; if I want or need something, then I have a reason to try to get it, and so, rationally I ought to. The altruist, by contrast, does seem to have a problem. How could it follow from the fact that you want or need something, that I ought to try and get it for you? How can the needs of others provide a compelling reason for me to act?
The previous chapter ended with the question 'On what could the demands of morality be based?' and this question raises just the same issue. Kantians and utilitarians both assemble evidence and argument to show that impartial reason and/or the general good point towards an individual's taking a certain course of action. But what reason is there for that individual to follow their prescription, especially if it implies some measure of self-sacrifice?
At this point we are taken back to the discussion of moral rationalism in Chapter 1 - the logical force of appealing to promises. One compelling reply to the question 'Why should I concern myself with the needs of others?' would be this: 'You promised to'. Immediately, this places the onus back on the egoist who asks the question, because the appeal is not