Besides these internal distinctions, principles must also be distinguished, so to speak, externally, from other standards of behaviour that can be part of a legal system.

Here, we assume that legal systems consist not only of mandatory norms, but also of other sentences (like permissive provisions, definitions and power-conferring rules, to be considered in the following chapters), and that mandatory norms can, in turn, be rules or principles.

The problem, therefore, can be formulated as follows: How can princi­ples be distinguished from rules? And, at the same time, what is the scope of the classifications of principles previously mentioned? Our strategy in answer­ing these questions will be to start from three typical approaches often adopted in dealing with norms and to apply them to the problem we are interested in.

The first one we can call the structural approach, because it consists in regarding norms as entities organized in a certain way. An example of this is the conception of norms to be found in Alchourron and Bulygin's Normative Systems (1971), where norms are conceived as sentences correlating generic cases (sets of properties) to solutions (that is, to the normative qualification of certain conducts).

The second typical way of understanding norms could be called function­al, since it concentrates on the role or function they — claim to — have in the practical reasoning of their addressees. An example of this approach in contem­porary legal theory would be especially the work of Joseph Raz, and one of H. L. A. Hart's later articles. As you may know, in those works norms are regarded as reasons for action; from this perspective, the fundamental interest is to show what kind of reasons norms are, and how they operate in practical reasoning.

The third approach is to look at norms not in terms of cases and solu­tions, or of reasons for action and practical reasoning, but in connection with the interests and power relations existing in a society. On the one hand, legal norms can be seen as the result or effect of certain social relations; on the other, legal norms themselves shape the relations between subjects by conferring powers and protecting the interests of some against others; and, finally, the power given to some individuals (or groups) by legal norms is used to change — or, more generally, to affect — social relations themselves. This third way of approaching norms — more closely linked to the sociology of law or the ideological critique of the law — is usually missing in the main currents of contemporary legal theory. In our view, that is a substantial deficit. As we will try to show later, taking into account this third perspective too can contribute enormously to a clarification of the role of principles in legal life.

Depending on which perspective one chooses for one's conception of norms, the question of how to distinguish principles from rules, or different kinds of principles from each other, can take on very different tones.

2.1.