‘After a period of frozen immobility the hardened mass of our substantive criminal law is at points softening and yielding to its critics.’ With this in mind Professor Hart considers in the first of these two lectures recent criticisms of the traditional legal doctrine that liability to conviction for serious crimes depends not only on the offender having done the outward act forbidden by the law but having done it in a certain state of mind or will ( mens rea ). He examines two variants of the view powerfully urged by Lady Wootton that if the aim of the law is to prevent crime the doctrine of mens rea is ‘illogical’ and should be allowed to wither away. In the second lecture Professor Hart returns to the topic of his past controversy with Lord Devlin over the enforcement of morals. He does so not to repeat the theoretical arguments but to distinguish different elements in a philosophy of punishment, long prevalent amongst English judges, and to consider the progress made and obstacles encountered by reformers who wish to remove the sanctions of the criminal law from suicide, certain forms of homosexual behavior, and abortion.