Efficacy
In the statutory law system, all legal norms that are effectively followed in society must be formally valid. Formal validity is a necessary precondition for efficacy, but not vice versa.
A formally valid norm is not necessarily effectively followed in the legal community. Desuetudo is a typical example of such a situation (Wroblewski 1992, 79). The notion of efficacy (axiological validity) in itself, however, can be understood in many ways (Wroblewski 1992, 79).A norm may be defined as being effective in a society if, and only if, the citizens regularly follow it. The Danish Professor in civil law, Knud Illum, a contemporary and colleague of Alf Ross, made this kind of proposal. According to him, the law is valid if, and only if, the citizens have experienced it as valid (Illum, 49). According to Illum, the “legal conviction” of the people is the measure for validity. It is a purely empirical question, whether the citizens follow the norm or not, which means that the validity of a legal norm is an empirical problem too. Ross accepted this view to a certain extent. Peoples' conceptions (borgernes retsakter) define the content of legal life (retslivet) in its broad sense. As we saw above, Ross did not otherwise accept Illum's view. For Ross, people's conception about legal issues is not the criterion of validity.
However, there are other proposals based on the notion of efficacy. One is formulated by Ilkka Niiniluoto. He has defined the validity as follows: The norm N is a valid legal norm if, and only If, it is accepted by the legal community C as part of the legal order (Niiniluoto 1981b, 168, 1985, 168). A proposition dealing with that kind of validity is always an empirical proposition that states something about the acceptance of N by C. There are several crucial points in that definition.
First, the notion of acceptance is problematic. According to Niiniluoto, it means “reasonable consensus”.
Most of the members of C accept N belonging to the legal order, which presupposes that the majority of C is committed to accepting N as valid. Yet, how to measure the majority (“most”)? Does the definition mean the dictatorship of majority because it does not give any protection to the minority? Niiniluoto does not give a reliable answer to that very question.The concept of legal community C is also difficult, maybe even impossible to define in an exact way. Who in the end are the members of that community: those who have a law degree, or also the laymen who are well acquainted with legal order, or maybe all those who are interested in law?
The third difficulty is intertwined with the notion of acceptance. The definition is an expression of an extreme positivism. It does not make any difference between the acceptance by rational means and acceptance produced by manipulation for instance. According to the definition, an extremely unjust law is also valid if it has been accepted by the majority of the legal community. Finally, the definition does not solve the problem of a new statute that has not yet been accepted by any member of the community but is certainly formally valid. It seems to me that this new statute is per definitionem not valid at all (Aarnio 1997, 170).
Summing up, all theories of validity based on empirical data are defective to such an extent that they cannot be accepted as the foundation of DSL. That is the main reason why the third notion of validity - that is, acceptability - becomes so important. It makes understandable the basic goal and purpose of DSL to reach as large an acceptability in society as possible. If DSL succeeds with this, it has fulfilled its social function as a source of reliable legal information.