The 6 Sources of Jewish Law [Menachem Elon]

Oral Torah comes from a variety of sources.  There is the core part of it that doesn't change (what I like to call the Core Oral Torah); and there is another part that does change.  Here again is Menachem Elon:

"Analysis reveals that there are six legal sources of Jewish law:

1.  Tradition (kabbalah).  Chronologically, the first of the legal sources is 'matters of tradition transmitted orally from person to person,' tracing back to their reception by Moses from God.  A legal rule derived from this legal source is transmitted from generation to generation.  This legal source is fundamentally different from the other legal sources of Jewish law in that it is inherently not amenable to development; it does not change but remains fixed--a static source of Jewish law.  In contrast, the other legal sources are inherently dynamic; in fact, a significant aspect of their function is to continue the creativity and development of Jewish law.

2.  Interpretation (midrash).  This includes the interpretation of Scripture and of the Halakhah in its different periods, and also, to a certain extent, other types of interpretation.

3.  Legislation (takkanah and gezerah).  This includes legislation by the halakhic authorities and by competent public bodies.

4.  Custom (minhag).  This includes various forms of custom and usage.

5.  Case or Incident (ma'aseh).  This refers to legal decisions and also to the personal conduct of halakhic authorities in particular real-life situations.

6.  Legal Reasoning (sevarah).  This is the process of legal and practical reasoning by the halakhic authorities.

     All of the last five legal sources serve as the recognized methods of the Jewish legal system for solving new legal and social problems, creating new legal rules, and changing existing legal rules where necessitated by changes in mores or in economic and social conditions," Menachem Elon, Jewish Law:  History, Sources, Principles, Vol.1, pgs. 238-239.