Two Rules of Legality in Criminal Law

78 Pages Posted: 3 Apr 2007

See all articles by Peter K. Westen

Peter K. Westen

University of Michigan Law School


Commentators approach legality in various ways. Some scholars eschew overarching principles and proceed directly to one or more of what they regard as distinct rules: (1) the rule against retroactive criminalization; (2) the rule that criminal statutes be construed narrowly; (3) the rule against judicial creation of common-law offenses; and (4) the rule that vague criminal statutes are void. Other scholars seek a single principle, i.e., the principle of legality, that they believe underlies the four rules. In contrast, I believe that both approaches are misguided. There is no such thing as a single principle of legality. Yet, the four aforementioned rules are not unrelated. The so-called principle of legality consists of two distinct norms that derive, respectively, from two fundamental principles of criminal justice, viz., the principle, No person shall be punished in the absence of a bad mind, and the principle that underlies the maxim, "Every person is presumed innocent until proven guilty."

The first norm of legality explains the rule regarding ex post facto legislation and the rules regarding notice and fair warning of judicial decisions. When a person is punished for violating a rule that was non-existent or unclear at the time he acted, he is punished for conduct that the state now condemns and seeks to prevent by means of penal sanctions. Accordingly, at the time the person is prosecuted, his claim is not that he did not do anything that the state regards as wrong, but, rather, that he neither knew nor should have known that he was doing something the state would come to regard as wrong. He ought, indeed, to be excused for his mistake, but only because of a principle that is common to excuses generally. It is the principle, "No person ought to be punished in the absence of a guilty mind." He should be excused because when a person does something the state condemns and wishes to prevent, he ought not to be blamed for it unless he was motivated in a certain way, namely, by an attitude of disrespect for the legitimate interests of the community by whose norms he is bound.

The second norm of legality informs several of the remaining rules, though not all of them. The second norm is that a person ought not be punished in the name of a community unless it can confidently be said that the community regards his conduct as deserving of the punishment at issue. It is a norm that is most commonly associated with the rule of lenity, but it is not confined to the construction of statutes that are ambiguous or vague. It can also be violated when a person is punished for violating a statute that has fallen into desuetude, regardless of how widely promulgated or narrowly defined the statute may be. The second norm derives from a principle that also underlies the presumption of innocence, the only difference between them being that the presumption of innocence is a preference for acquittal in the event of uncertainty regarding the facts with which an actor is charged, while the second norm of legality is a preference for acquittal in the event of uncertainty regarding the scope of the offense with which he is charged. Nevertheless, one rule remains that this analysis throws into question, namely, the rule that vague criminal statutes are void. Criminal statutes are sometimes so broadly defined that they do, indeed, infringe constitutionally protected rights of speech, movement, etc., in which event they ought to be invalidated on those very grounds. And criminal statutes are sometimes so broadly drafted that, before applying them, courts ought to construe them to apply only to constitutionally unprotected acts that courts can confidently say the relevant political community regards as warranting punishment. But once statutes are construed to apply only to constitutionally unprotected conduct, courts have no further reason to invalidate them on grounds of vagueness. Lack of notice is no reason to invalidate them because, with respect to the narrowly defined conduct such statutes are construed to prohibit, common social duty alone ought to alert actors that their conduct is suspect.

Suggested Citation

Westen, Peter K., Two Rules of Legality in Criminal Law. Law and Philosophy, Vol. 26, No. 3, pp. 229-305, May 2007, U of Michigan Public Law Working Paper No. 78, Available at SSRN:

Peter K. Westen (Contact Author)

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