A detailed argument is made in support of the position that a mistake about consent should be acceptable as a good answer to a rape charge only if the mistake was reasonable. It is also suggested that the concept of mens rea cannot be adequately explained with respect to a particular offense without analyzing the nature of the conduct involved in that offense. Contrary to the views of Glanville Williams, which are now having a strong influence on judicial decisionmaking in Canada, the author contends that whether a particular mental state should be treated as culpable depends upon the action to which it relates. The act of rape is always intentional, but whether the act is harmful in a particular instance cannot be determined without reference to the environment and the situation. Failure to inquire carefully into consent aspects in alleged rape cases is unfair to the defendant. When prompted by an honest mistake, wrongdoing does not necessarily justify criminal punishment. Case law has not adequately addressed the issue with respect to all crimes requiring mens rea; little sound reasoning is evident in support of decisions holding that an honest mistake about consent is a good answer to a rape charge. More direct concentration on the nature of the conduct prohibited by each offense will lead the courts to refine the concept of mens rea and to bring the legal concept into better alignment with the fundamental notions of blameworthiness it was designed to embody. The article includes 73 footnotes.