Laws which are created through interpretation (hermeneutical principles, textual analysis or logic)
The first issue in discussing this category is if it exists at all! There are those Rishonim and Achronim, most notebly R. Avraham b. Daud in Sefer ha'Kabbalah, that maintain that all of halakha, even those which seem to have been created through interpretation, were transmitted from Moshe.This is excluding, of course, rabbinic enactments. These authorities then must account for the clear existence of disagreement among the Tannaim and Amoraim regarding the law and exegesis.
R. Yitzchak Isaac Halevy (Dorot HaRishonim 1:3:29 and 4:7) has a slightly different approach. He maintains that the Sages based their conclusions solely upon their analysis of statements and of precedents made and set by former authorities. Only after they arrived at their conclusions through such means did they attach a derasha to support themselves. R. Zvi Lampel writes that this approach is not in accordance with a simple reading of the Talmud or the opinions of the Rishonim. For example, see Bava Metzia 5a, Gitten 39a , Temurah 6b, Shabbat 13a where a derasha seems to be the source of the law. Nevertheless, this opinion of the Dorot ha'Rishonim is important, for, as R. Lampel himself points out, the Sages often had multiple reasons for an interpretation (see Eruvin 22a and Yevamot 16a).
However, the approach that we will follow and mainly discuss is that of the Rambam in Hakdama l’peirush ha’Mishnayot, Sefer ha'Mitzvot, Shoresh Shayni (s.v. "rov dinei ha'Torah"). and Hakdama l'Mishna Torah. Therein he maintains that in addition to transmitting received laws, the Sages derived new interpretations through use of the thirteen rules of interpretation, commonly accepted legal principles, and received definition of terms. Thus, new laws were subject to dispute and re-analysis (see Hilkot Mamrim, 2:1). Other Rishonim that are similar to the Rambam's approach include the Ran (Derashot ha’Ran, Drush shevi’i) and Ritva (Eruvin 13b).
The Biblical source that grants the Sages, at least in the form of the Sanhedrin, the authority rule in judicial matters is Devarim 17:8-11. Other verses that indicate a local judicial system and its binding nature are: Devarim 16:18, 21:19, 22:16. However, these verses do not specifically inform us about the methodology that the judicial system used. Furthermore, there is a major debate among Talmudic commentators about the binding nature of non-judicial authorities (i.e. why did the Amoraim refrain from disagreeing with the Tannaim etc.) See R. Zvi Lampel, Dynamics of Dispute, pgs. 107-121.
In the new post we will discuss the methodology of Rabbinic interpretation.