Mens rea, as was explained in chapter 1, is the state of mind which must be present in an accused if his overt action is to constitute a crime, and if he is to be held responsible for it. This general notion fits different crimes in different ways. Criminal laws differ not only in respect of the overt actions they forbid (as murder differs from rape) but also in respect of the state of mind which they require if the action is to constitute the offence in question (as murder differs from manslaughter).