"According to Masechet Sanhedrin [5a], there are two requirements for one who wants to exercise rabbinic authority—one must be both gamirna and savirna. Now, what do these Aramaic terms mean? Gamirna implies that one has to have amassed sufficient knowledge or learning. Basically, they gotta know their stuff. And savirna implies they have to have the ability to exercise svara. But what is this svara that is so crucial to functioning as a rabbi and to interpreting God’s will? It seems pretty straightforward: svara, the ability to be “savir,” “reasonable.” The capacity to reason. But, actually, svara is much more complicated, and, it turns out, is not only a prerequisite for those aspiring to rabbinic authority, but is probably the most significant source of Jewish law we have.
After the destruction of the Second Temple, our founding Rabbis increased the number of places to which they could turn to discover God’s will—that is, the sources of Jewish Law—from one to five. In addition to our old standby—a verse in the Torah, which they called kra (and which legal scholars call midrash)—they added ma’aseh (precedent), minhag (custom), takkanah(legislation) and last but not least, svara.
Menachem Elon, the most prominent Jewish legal scholar of our generation and former Justice and Deputy President of the Israeli Supreme Court, defines svara as “legal reasoning that penetrates into the essence of things and reflects a profound understanding of human nature [and involves] an appreciation of the characteristics of human beings in their social relationships, and a careful study of the real world and its manifestations.” [Elon, Jewish Law: Cases and Materials, Mathew Bender, 1999, p. 97] This is just a fancy way of saying: what your kishkes, and your intellect, and your experience of human nature and the world around you (which should be extensive), tell you about what’s right and what’s wrong.
That a person’s svara is a legitimate place to look to figure out what God wants of you is radical enough. But wait: As we all know, laws which the Rabbis derived from kra, or biblical verses, were given the status of d’oraita—directly from Torah, transmitted directly from God to Moshe on Mount Sinai. And laws deriving from ma’aseh (precedent), minhag (custom), or takkanah (legislation) were acknowledged as being of human derivation—a creation of the Rabbis themselves—and were labeled merely d’rabbanan, a kind of “second-string” as far as laws went.
But—get this—a law that the Rabbis created by means of svara was classified as—now put your seatbelts on for this one—d’oraita. What comes from our kishkes, said the Rabbis, is really coming straight from God—from God to Moshe on Mt. Sinai to me. Svara, according the Rabbis, had the same authority as the biblical text itself—and in many instances in the Talmud, svara trumps kra—kishkes trump a biblical verse."-From "Torah,Queers and the Future of Rabbinic Judaism",Rabbi Benay Lappe
"But even after you have gained your conception of God from the Torah,beware above all of your sensory understanding,of applying to God the standards of the senses,and thinking that for understanding you have answered questions about God and His Providence though you have not found either of them in the sensous understanding.Your understanding is competent only to investigate the created world;for that purpose it was given to you.That world is the sphere of your activity,and only as far as it is the sphere of your activity,and only as far as it is the sphere of your activity is your understanding adequate.But God is not creature,so beware of trying to measure the creator with the yardstick of the creature"-From Horeb,Rabbi Samsom Raphael Hirsch