Substantive rules of law (such as the rules of torts, contract, and property) are usually assumed to be addressed to two audiences. As conduct rules, the substantive law is addressed to everyone (citizens, officials, and noncitizens). Thus, property law tells us who has dominion over which resources. If this land is mine, then the law communicates the message that I can use my land and exclude others from its use. These very same legal rules also serve as decision rules, they tell courts how to resolve disputes. We usually assume that the content of the conduct rules are the decision rules are identical, but this need not be the case.
Professor Meir Dan-Cohen of U.C. Berkeley proposed a very famous thought experiment. He asked us to imagine acoustic separation between ordinary citizens, who would only "hear" the conduct rules, and officials (such as judges), to whom the decision rules would be addressed. You might imagine that courtrooms are isolated by a giant "cone of silence".
Dan-Cohen's thought experiment leads naturally to the following question: should decision rules and conduct rules have the same content or should they differ? And if they differ, how could the law prevent acoustic leakage, e.g. prevent ordinary citizens from learning about the content of the decision rules?
Here's a pretty clear example. Suppose that we have a conduct rule that says, "Ignorance of the law is no excuse." This might be a good conduct rule, because we want citizens to inform themselves about the content of the law, and we certainly don't want citizens deliberately insulating themselves from knowledge of the law in order to create a defense if they charged with its violation. But at the same time, we might prefer that ignorance of the law would serve as an excuse, at least some of the time, when it comes to actually convicting and punishing defendants. Punishment is expensive and injurious, and sometimes no really good purpose will be served by punishing someone who is reasonably ignorant of the law's content.
The Technology of Acoustice Separation
But how can we excuse ignorance of the law without altering the conduct rule? One way to accomplish this goal would involve some obfuscation by judges. Opinions might state boldly: "Ignorance of the law is no excuse," while simultaneously excusing ignorant defendants on the ground that "knowledge of the legal status of the intentional content is part of the mental state that is an element of the crime." The first formulation is easily accessible to ordinary folks; the second is couched in language that may be opaque except to those trained in the law.
Even if it is possible to create acoustic separation between conduct rules and decision rules, doing so may be problematic on normative grounds. For utilitarians or welfarists, the only question is whether acoustic separation will produce good consequences, but for fairness-based (or deontological) approaches, the deception involved in acoustic separation seems problematic. This intuition is reflected in a variety of legal doctrines (such as the "void for vagueness" doctrine in constitutional law) and in the notion of "publicity" that is usually included in formulations of the ideal of the rule of law.
Using the Distinction
The distinction between conduct rules and decision rules may not arise frequently--because the conditions for acoustic separation may be rare and because the law usually aims at congruence between the two sorts of rules, but in almost every legal context the distinction could become relevant. It is almost always worth asking, "Is there any discrepancy between the conduct rules and decision rules in this area of law?" And if there is such a discrepancy, then further questions are in order: "Is this accidental or does it serve some function?" and "Is this instance of acoustic separation normatively justified?"
Meir Dan-Cohen Decision Rules and Conduct rules: On Acoustic Separation in Criminal Law, 97 Harvard Law Review 625 (1984) (available to subscribers on Jstor and anthologized in Meir Dan-Cohen, Harmful Thoughts: Essays on Law, Self, and Morality(Cambridge University Press 2002).
Criminal Law Conversations (Paul H. Robinson, Stephen Garvey, & Kimberley Kessler Ferzan eds., Oxford University Press 2009). This volume contains several essays that comment on Dan-Cohen's idea.
Paul H. Robinson, Rules of Conduct and Principles of Adjudication, 57 U. Chi. L. Rev. 729 (1990).
(Last modified on May 19, 2013.)