The Gemara on top of amud Beis tells us a rule that we do not use a kal v’chomer inference to derive a new Halakha from a halakha l’moshe misinai. That is a purely oral tradition with no source in the scripture cannot be used as a source to make additional derivations via kal v’chomer, and according to many commentaries, any of the 13 hermeneutical principles. 

We should ask, what is the reason for this position? Especially in regard to many of the principles that have an obvious logic such as kal v’chomer and binyan Av?

The Benei Yissaschar (Sivan 6:4) offers an explanation that is difficult to fully understand but I will try to give it over and attempt a stab at its deeper meaning. Literally the Benei Yissaschar asserts that the derashos of the thirteen hermeneutical principles are the same as the 13 attributes of mercy. When applied to laws based in scripture, they represent a softening of the harsh aspects of Torah law with Oral law. Oral law represents middas Harachamim (merciful attributes of G-d) while the written law represents middas Hadin the attribute of strict justice. Literally, the “Letter of the Law”. As such, a totally oral law cannot be balanced out with a hermeneutical principle, since both already represent middas HaRachamim. Only a scriptural law needs to be balanced by the oral law.

Let’s try to understand this more deeply. the written and oral law most definitely symbolically represent strict justice and mercy respectively. Think about it, any unwritten law is more flexible than a written law. Even more powerfully, written laws themselves are subject to unwritten merciful application in the real world. My good friend and scholar, Vukan Marinkovic a brilliant Torah light from Croatia, pointed out that the sign might say “speed limit 55” but no policeman would enforce it unless you are going perhaps in excess of 65 MPH. 

This seems to be an ontological truth about the written law. There are numerous examples we can give to this, however let me provide some obvious ones. The literal verse is that one must take an eye for an eye, but the rabbinic tradition, in other words the oral law, is that it refers to monetary compensation (Bava Kama 83b). The literal verse states up to 40 lashes (Devarim 25:3), the oral tradition is no more than 39 (Makkos 22). The literal verse invalidates a sacrifice and makes the owner RETROACTIVELY liable for punishment based on the action of someone eating from the sacrifice beyond its correct time (Vayikra 7:18), but the oral law only creates future liability based on past actions (see Rashi Op. Cit). 

There are many other examples. What I hope the listener will reflect on is how deeply significant this concept is and what it truly means in terms of the practice and execution of halakha.