Our Gemara on Amud Beis discusses whether a stream pouring from one vessel to another constitutes a halachic connection (nitzok chibbur)—such that wine in the upper vessel remains kosher even if poured into yeyn nesech.
Rav Hunah rules that regarding yeyn nesech, a downward stream is considered a connection. Even though gravity ensures the flow never returns upward, the continuum binds them. In modern terms, we might think of it like electrical conduction. Yet Rav Hunah agrees that in ritual impurity, as taught in Mishna Taharos (8:9), a stream does not transmit impurity or join waters for mikveh.
Why the difference? One could say simply that the rabbis were stricter with yeyn nesech. Yet halachically we seek deeper reasoning. For impurity, since the liquid cannot flow upward, it is not considered connected. But yeyn nesech tolerates no appearance of connection, because the social and financial temptation to rationalize is intense, so even downward flow is treated stringently.
From a metaphysical perspective, Kli Yakkar (Devarim 32:1) applies this to heaven and earth. Moshe calls heaven and earth as witnesses (Rashi, Sifrei Devarim 306:15). Beyond accountability, they embody sustenance and existence. Kli Yakkar explains: heaven and earth are opposites requiring a human intermediary, uniting matter and form through Torah. Torah connects heaven and earth like rain: “Let my teaching drop as the rain” (Devarim 32:2). Thus Torah is nitzok chibbur—a downward flow that connects realms.
But doesn’t our Gemara teach that a stream downward is not a connection? The answer lies in the mystical principle: “the lower realm arouses the upper” (Ohr HaChaim, Shemos 19:3, quoting Zohar III:92a). Spiritual flow becomes reciprocal: when humans arouse heaven, heaven responds. Thus, only when there is both downward and upward motion does the flow truly constitute nitzok chibbur.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation
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Rabbi Simcha Feuerman, Rabbi Simcha Feuerman, LCSW-R, LMFT, DHL is a psychotherapist who works with high conflict couples and families. He can be reached via email at simchafeuerman@gmail.com