The living law is the law which dominates life itself even though it has not been posited in legal propositions. The source of our knowledge of this law is, first the modern legal document, secondly, direct observation of life, of commerce, of customs and usages and of all associations, not only those that the law has recognized but also those that it has overlooked and passed by, indeed even those that it has disapproved.

Eugen Ehrlich, Fundamental Principles of the Sociology of Law, p. 493.