It is usual for Parliamentary draftsmen to express rules of criminal law as directions to courts, laying down the necessary and sufficient conditions for a conviction.' Textbook writers and reform bodies have, in large part, followed that view.2 Rules of criminal law may also, of course, be treated as rules governing conductguidelines as to what behaviour is and what is not tolerable. Now although the problem whether laws should be perceived as being directed primarily towards courts or subjects is one which has been of concern to legal philosophers for many years,3 it has largely been assumed by criminal law scholars that the distinction has little or no significance for their discipline. That is, when the law says that anyone who is guilty of X shall be liable to this or that penalty, it may just as well be understood as saying that people ought not to do X, and conversely that when the law is that Y generates an acquittal that means that Y is It is assumed to follow from this that when a court finds a defendant guilty, that decision embodies and promulgates a norm that the conduct in question is forbidden (a proposition from which it is difficult to dissent) but also that when there is an acquittal the conduct in question is permitted. Two further factors serve to strengthen this view. First, there is the emphasis of academic study of law upon decided cases. Second, practising criminal lawyers deal almost exclusively with facts which have taken place. Whereas tax lawyers advise upon the consequences of 'acts in the law', so as to allow their clients to organize their affairs in such a way as to avoid or minimize liability, there are few if any criminal lawyers who advise upon just how close to the wind, for example, the would-be racketeer5