WE have found it necessary, in order to elucidate features
distinctive of law as a means of social control, to introduce
elements which cannot be constructed out of the ideas of an
order, a threat, obedience, habits, and generality. Too much
that is characteristic of law is distorted by the effort to explain
it in these simple terms. Thus we found it necessary to
distinguish from the idea of a general habit that of a social
rule, and to emphasize the internal aspect of rules manifested
in their use as guiding and critical standards of conduct. We
then distinguished among rules between primary rules of
obligation and secondary rules of recognition, change, and
adjudication. The main theme of this book is that so many of
the distinctive operations of the law, and so many of the ideas
which constitute the framework of legal thought, require for
their elucidation reference to one or both of these two types
of rule, that their union may be justly regarded as the
'essence' oflaw, though they may not always be found together
wherever the word 'law' is correctly used. Our justification
for assigning to the union of primary and secondary rules this
central place is not that they will there do the work of a
dictionary, but that they have great explanatory power.