Casual Legal Realism?

Positivism, Realism, and Sources of Law' by Leslie Green in Mindus and Spaak (eds), The Cambridge Companion to Legal Positivism (Cambridge University Press, 2019) comments 

 This paper explores the relationships between legal positivism and legal realism. Legal positivists hold that all law is positive law, that it is based on social sources. The law is therefore incomplete: there are legal disputes that cannot be determined by law alone. But legal realists seem to presuppose that all law is positive, and they affirm that, at least in appellate cases, judicial decisions are underdetermined by positive law. Are realists therefore legal positivists? In temper and outlook the doctrines are similar. My argument is that, after some conceptual errors are set aside, one difference lies in their respective attitudes to sources of law. Positivists hold that many sources of law are binding, at least on judges. Legal realists hold that many sources are permissive only: even domestic statutes and cases often have little more authority than, e.g. a doctrine of foreign law. That, in addition to the more familiar sources of indeterminacy acknowledged by positivists and realists alike, helps explain why realists think law is so loosely controlling in court, and why it is often defeated by considerations of policy and preference.