Within jurisprudence several principles have been suggested for the task of classifying legal norrns. The logical implication of the different classes is varied. The question addressed here is if any of the proposed classifications exhibits characteristics making it particularly weIl adapted to serve as a basis for a computable logical formalism for legal reasoning. Criteria for choosing an appropriate principle are compiled and the different classifications are juxtaposed and compared in the light of these criteria. It is argued that among the existing classifications the functional is the most suitable one and this approach is analyzed in sorne detail. This analyze indicates the need of subsequent studies to find answers to the following questions: (i) which are the different (a) legal functions, (b) generalized needs, and (c) logical structures for legal norms? (ii) is it possible to develop a methodology for propagating semantical constrains through hierarchies consisting of legal principles, generalized needs, and legal functions?