If each man must always pursue his own pleasure, ethics is reduced to prudence
 Bertrand Russell, A History of Western Philosophy (1945). copy citation

Context

“if each man in fact and inevitably pursues his own pleasure, there is no point in saying he ought to do something else. Kant urged that “you ought” implies “you can”; conversely, if you cannot, it is futile to say you ought. If each man must always pursue his own pleasure, ethics is reduced to prudence: you may do well to further the interests of others in the hope that they in turn will further yours. Similarly in politics all co-operation is a matter of log-rolling. From the premisses of the utilitarians no other conclusion is validly deducible.” source