Nedarim 6a: Yad in Nedarim vs. Kiddushin and Gittin

The Gemara (גמרא) on Nedarim 6a raises a fundamental question: why does yad — an incomplete verbal formulation — work for nedarim (vows) but not for kiddushin (marriage), even though both involve verbal declarations? The shiur begins by noting that the Ran suggests a distinction based on whether a ma'aseh (physical action) accompanies the words: nedarim work through speech alone, while kiddushin require a ma'aseh. This raises the question of gittin (divorce), which also require a ma'aseh — why would yad work there? Rabbi Zweig develops a fundamental yesod to resolve this difficulty. Nedarim are fundamentally different from kiddushin in their very nature. A neder is a personal, unilateral statement. When someone makes a neder, it affects only himself and his property. Even when a neder prohibits one's property to another person, it remains the speaker's action on his own property — not a bilateral transaction. Therefore, for nedarim, what matters is only that the speaker himself knows clearly what he means. The requirement is internal clarity and personal conviction, not external communication. Yad works for nedarim because as long as the person making the vow knows what he intended, that suffices — even if an outside observer wouldn't necessarily understand from the words alone.