Most philosophers who have written about morn weakness assume that knowingly violating one's principles is paradigmatic of moral weakness. A standard example of knowingly violating one's principle would be: Jones accepts the moral principle 'adultery is wrong'. If Jones applies his principle successfully to a particular case -ought he to make love to Mary Smith -and concludes that he ought not to since doing so would violate his principle, yet he proceeds to make love to Mary Smith all the same, he knowingly violates his professed principle. I shall call such cases of knowingly violating one's principle cases of spinelessness. 1 There are many types of moral weakness in addition to spinelessness. It is quite important to make explicit that there is a wide range of moral weakness cases, both in order to get a grasp on what morn weakness is and to understand the implications of denying that moral weakness ever genuinely occurs. For if, as is argued by Hare and Santos, all putative instances of moral weakness are really instances of actions done by agents who are not sincere acceptors of the principles they profess or instances of acting under a compulsion, then fewer of us than is commonly supposed accept the principles we profess to accept. The genuine acceptance of a principle is a rare achievement.
An agent is said to be morally weak if and only if and he fails to act, when it is in his power to do so, in conformity with an applicable moral principle he accepts. A full explication of the important concepts employed in this definition would be very lengthy indeed. I shall limit my account to those features of the concepts of 'accepting a morn principle' and 'acting voluntarily' which are relevant to understanding that there are many types of moral weakness. The first two sections of this essay will be devoted to the relevant features of these concepts; the third to expounding eight types of moral weakness.