Kiddushin 5ab: Kinyan Kesef vs. Chuppah and the Nature of Ishus

This shiur analyzes the Gemara (גמרא)'s two attempts to prove through kal vachomer that chuppah should be able to effect erusin. The first kal vachomer argues from kesef she'eino mechol—kesef does not permit an arussa bas Yisrael to eat terumah, while chuppah does. Since kesef creates erusin, chuppah, which has the additional power of mechol, should surely create erusin. The Gemara rejects this because the very kinyan of kesef itself is mechol according to Ulla, so there is no advantage to chuppah in this regard. Rabbi Zweig addresses a fundamental question: why does the Gemara include this first, flawed kal vachomer at all? We already know from Ulla in other places in Shas that an arussa eats terumah mid'rabbanan. The shiur could have simply started with the correct kal vachomer. The answer reveals a profound insight into the nature of erusin: the Gemara is teaching that erusin is not merely a standard kinyan governed by hilchos kinyanim, but rather a kinyan of ishus—a relationship. The first kal vachomer establishes that if chuppah were to work for erusin, it would work because it creates ishus, not because it is a superior form of kinyan in technical terms.