The written and oral Torahs are generally connected, even if that connection is not always clear. Oral laws were given as a tradition to Moshe and were transmitted over the generations. However, it is not always easy to remember lists of laws so various generations sought to support these laws from the biblical text. Some place the generation of Ezra, when a religious revival took place, as a time when there was a major effort to connect the two Torahs. Regardless of the timing, this leads to a division among oral halakhos. The Rambam, in his introduction to his commentary on the Mishnah, distinguishes between oral laws that have no connection to the biblical text at all (described by the Mishnah in Hagigah as “floating in the air”), laws whose connection to the text was given to Moshe and transmitted along with the law and laws whose connection to the Bible was found afterwards. This connection to the text does not mean that it is merely a fiction useful for study. It is very real. As the Vilna Gaon emphasized, almost all halakhos can be found in the Bible. The methodologies used show how we could have derived them from the text had we not already known them.
There is a fourth category of oral laws, at least according to the Rambam. There exist laws that are created by the Sages through biblical exegesis. Using accepted methodologies, the rabbis derive laws from the Torah that were previously unknown. It is this last category that we will discuss here.
While the Rambam acknowledges that such a category exists, others deny that the Sages ever created new laws through hermeneutics. R. Sherira Gaon, in his famous epistle about the history of the oral Torah, mentions derashos that support existing laws but does not mention derashos that create laws. Similarly, his son, R. Hai Gaon, wrote in a responsum that derashos only support the law and do not create it. Thus, while the Rambam agrees that there are derashos that only support the law, he argues that there are also derashos that create laws while the Geonim deny that such derashos exist.
For example, everyone agrees that the “peri etz hadar” one must take on Sukkos is a citron. The varying derivations of this law in the Talmud are only ex post facto supportive derashos and not attempts to create a new law through hermeneutics. However, when Beis Shammai say that one must lie down at night and stand up in the morning while reciting the Shema (Berakhos 10b), were they extracting this idea from the verse or merely assuming that the existing practice was obligatory rather than just customary? Similarly, when Beis Shammai say that a man can only divorce his wife if he finds in her a devar ervah (Gittin 90a), is that a law derived directly from the verse or was the verse used only as a proof? This is the debate over whether derashos are creative or merely supportive.
In his Sefer Ha-Mitzvos (shoresh 2), the Rambam repeats that there are derashos that create halakhos but implies that such laws are only of rabbinic force. The Ramban, in his glosses, agrees that there are laws created in such a fashion but argues strongly that they are of biblical force. The standard resolution of this debate is offered by Ramban’s descendant, R. Shimon ben Tzemah Duran (Rashbatz), in his Zohar Ha-Raki’a. He suggests that the Rambam also meant that these laws are of biblical status but that their origin is from the rabbis. The only difference between the Rambam and the Ramban, then, is how to identify laws that were created rather than supported. While this explanation is the most accepted, there are some who believe that the Rambam was of the view that halakhos cannot be created through hermeneutics other than on a rabbinic level.
Throughout the ages, various scholars have taken sides on this issue. For example, Hakham David Nieto (1654-1728) in his Mateh Dan – Kuzari Sheni (3:5-14) argues that creative derashos were used, but only in the case of a forgotten law or when a new situation arose that had not been previously addressed.
This debate continued to modern times among both traditional rabbinic scholars and university academics. R. Meir Leibush Weiser (“Malbim”) wrote a commentary to the Torah, Ha-Torah Ve-Ha-Mitzvah, that attempted to show the hermeneutical methodologies of derashos. His work can be seen as being on either side of the debate, as even those who claim that derashos only support laws agree that the derashos must be methodologically sound. However, in the introduction to his grammatical preface to his commentary to Vayikra, Ayeles Ha-Shahar, Malbim goes one step further and states that most derashos are creative. In response to this, and to earlier academics like Krochmal, Frankel and Weiss who agreed, R. Yitzhak Isaac Halevy wrote at length on this subject in which he harshly condemned this approach and argued that almost all derashos are supportive. I emphasize “almost all” because his position is frequently misquoted in the literature on this subject. Halevy did not disagree with the Rambam because he allowed for creative derashos in the very limited context of an authorized Sanhedrin. Even he, the most extreme of all scholars on this subject, allowed for some creative derashos. However, he strongly denied that, for example, the derashos of R. Yohanan and Resh Lakish were anything other than supportive exercises.
In terms of academic scholars, it is noteworthy that R. Ya’akov Nahum Epstein accepted Halevy’s thesis. However, as already noted, the early academic scholars of Torah took a wider approach to creative derashos and that has generally remained dominant in the field. Hanokh Albeck brings a number of strong arguments in favor of creative derashos, albeit accepting that many – perhaps most – are supportive. Ephraim Urbach adopts an innovative theory that there were two opposing factions throughout the Second Commonwealth and the Tannaitic era, one favoring creative derashos and the other opposing. During various times throughout that period one faction might have been more influential than the other, but overall the creative faction gained dominance in the final generations of the Tannaitic era. Ultimately, his theory is too elegantly contrived to withstand scrutiny and remains, to this writer, more a figment of Urbach’s imagination than an historical reality.
R. Avraham Weiss also accepts that derashos can be creative. Building on this, his student R. Hayim Yitzhak Levin notes the following phenomenon. A derashah can be brought as support for a pre-existing halakhah. However, when that support is accepted as adequate, when it is decided that had we not known of this halakhah beforehand this derashah would have been sufficient to create this law, then the derashah can be used to create new details of this law.
The methodologies of halakhic midrash are complex and require a sensitivity to the biblical text as well as a legal outlook. Not everyone recognizes the subtleties that underly derashos. However, it is crucial for any student to recognize that not all derashos were used to create laws. Many were ex post facto attempts to synthesize the oral and written Torahs. Even if this is not true of all derashos, it is quite possibly true of most and perhaps almost all of them. This recognition may not be important to many people. However, students who find derashos implausible should keep in mind 1) that there is a sensitivity required to appreciate the methodologies of derashos and 2) by and large, these derashos are supportive and not creative.
 Qafih tr., vol. 1 p. 11. Cf. Mishneh Torah, Hilkhos Mamrim 1:1.
 Levin ed., p. 39
 Teshuvos Geonim, ed. Assaf, no. 14. Cf. however, Hanokh Albeck, Mavo Le-Mishnah, p. 54 n. 21 who harshly criticizes Epstein’s interpretation of this responsum.
 Cited in the commentaries to Sefer Ha-Mitzvos, shoresh 2, e.g. Megillas Esther no. 2.
 On this, see Doros Ha-Rishonim, vol. 5 p. 503 ff.
 E.g. R. Yosef Qafih, Kesavim, vol. 2 p. 549 ff.
 Doros Ha-Rishonim, 1:3 (vol. 2) pp. 307-311, vol. 5 pp. 467-543.
 R. Nosson Kamenetsky, Making of a Godol, p. 14 n. n records that R. Ya’akov Kamenetsky took offense at the harshness of this criticism.
 Mevo’os Le-Sifrus Ha-Tanna’im, pp. 501-515
 Mavo Le-Mishnah, ch. 3
 “Ha-Derashah Ki-Yesod Ha-Halakhah U-Va’ayas Ha-Soferim” in Tarbitz 27
 Le-Heker Ha-Talmud, p. 13
 “Al Yahas Ha-Halakhos Ve-Ha-Derashos” in Sefer Ha-Yovel Le-Rav Avraham Weiss
I don’t understand the opinion of R. Yosef Qafih who says that according to the Rambam, one must obey the drashos on a rabbinic level. Isn’t the Rambam the one who holds that all rabbinic decrees are included in lo sasur, hence being of Torah origin. So what in essence is the difference? If one is not allowed to divorce a wife without finding a dvar erva, is this a function of hilchos gittin or hilchos lo sasur. It seems that it all boils down to this. But not much of a distinction.