Full Idea
For the positivist, law is law by virtue of its form; for the naturalist, by virtue of its content.
Clarification
'Naturalists' believe in natural law
Gist of Idea
For positivists law is a matter of form, for naturalists it is a matter of content
Source
Roger Scruton (A Dictionary of Political Thought [1982], 'law')
Book Reference
Scruton,Roger: 'A Dictionary of Political Thought' [Pan 1983], p.259
A Reaction
Clearly a perverse and 'unnatural' social rule (backed by government and implied force) is a 'law' in some sense of the word. It is hard to see how you could gain social consensus for a law if it didn't appear in some way to be 'natural justice'.