Chullin 116

Sugya Map: The Mechanics of Binyan Av

• Issue: The formal rules of Hekkesh and Binyan Av (inferential derivation).
• Nafka Mina: Whether a pircha (refutation) requires a specific structural imbalance (kolah v’chumrah) or can be any arbitrary unique factor (kol d’hu).
• Primary Sources: Chullin 116a, Deuteronomy 22:9, Deuteronomy 14:21.

Text Snapshot

The Gemara establishes the hierarchy of derivation:

"חדא מחדא... פרכינן קולא וחומרא... חדא מתרתי... אפילו כל דהו פרכינן" (One from one: refute via leniency/stringency. One from two: refute via any unique factor.)

Rashi (s.v. Chad min trei) notes the nuance: even if the logic does not "revert" (lo hadar dina), once you rely on two sources, the threshold for refutation drops significantly—any distinguishing feature suffices.

Readings

• Rashi (116a): Distinguishes between the "strength" of the source. A single source is a weak anchor; one must prove the pircha has structural weight. Once you have two sources, the "commonality" (tzad ha-shaveh) is robust enough that any discrepancy is a valid challenge.
• Tosafot (116a s.v. Chad min trei): Discusses the "reverting" rule (hadar dina). They query why we don't immediately refute using Chametz B’Pesach (as a source for B’shul) if it has a unique stringency. They conclude that if the tzad ha-shaveh is sufficiently broad, the logic holds unless a specific kolah v’chumrah is identified.

Friction

• Kushya: If we infer Basar b’Chalav from Kilayim (Vineyard), why isn't the fact that Kilayim lacks a "time of fitness" (sha'ah she-lo hayta ra'uyah) an automatic pircha?
• Terutz: Rav Adda bar Ahava shifts the definition of the prohibition: if the roots of the vineyard are prohibited, then the premise of "no time of fitness" vanishes. The pircha fails because the underlying tzad ha-shaveh (produce) remains intact.

Intertext

• SA Yoreh Deah 87:1: The application of these exclusionary logic rules manifests in the strict prohibition of Basar b’Chalav, where the derashot of "Gedi" (excluded wild animals/birds) limit the Torah scope, creating the halachic distinction between de-oraita and de-rabbanan status.

Psak/Practice

The meta-psak heuristic here is the "rigor of the anchor." In Issurim, one cannot broaden a prohibition via a fortiori unless the source is structurally symmetric. If the source cases possess unique stringencies, the tzad ha-shaveh must be proven to transcend those individual quirks.

Takeaway

In logic as in law: the more sources you stack, the easier it is to be refuted by a single detail. Don't over-rely on a single binyan av if the source cases contain idiosyncratic stringencies.