‘And He Simply Said: Bread’
Shmuel, on our daf, cites a rule: “If a person resolves mentally to swear [to prohibit something upon himself], it is only valid if he utters it with his lips.” He derives this rule from Vayikra 5:4: “Or if a person will swear, expressing his lips to do harm or to do good, anything that a person will express in an oath, but it was concealed from him, and then he knew, and he became guilty regarding one of these matters.”
The Gemara clarifies that one’s thoughts are not completely irrelevant. If someone, for example, mentally resolves not to eat “bread made from wheat” but vows not to eat “bread” – generically – the vow only applies to bread made from wheat.
Tosafos (s.v. “gamar b’libo”) questions this ruling based on another one in the Gemara (Nedarim 27b) that indicates that one may not limit the scope of one’s oath. The Gemara says that if a person arguing with his friend says, “I swear not to eat food if I am wrong,” he can’t later say he meant he would only not eat that day. The Gemara rules that since he didn’t say “today,” he presumably meant “forever.”
Tosafos reconciles the two rulings by suggesting that “bread” generally refers to bread made from wheat. That’s why he can later say he meant “bread made from wheat” even though he only said “bread.” In contrast, when someone says “I won’t eat,” there is no reason to believe him when he later says he meant he would only not eat that day.
A Slip Of The Tongue
The Ramban (Novella ad. loc.), in answer to Tosafos’s question, explains that failing to specify “bread made from wheat” is a “slip of the tongue,” and, as a rule, a person is not bound by an oath uttered in error due to a slip of the tongue. He cites our Gemara which states that a person who swore not to eat bread made from barley may eat it nonetheless if he really meant to say bread made from wheat. Not only that, but since he did not say bread made from wheat, he may eat that kind of bread too!
A Stitch In Time…
The Rosh (Nedarim 16a, 2:6) says that if a person tells his friend, “I swear I won’t eat your food,” he is not believed to subsequently say that he really meant to say, “I will eat your food.” The Bach (Yoreh Deah 237 s.v. “amar la’chaveiro”) wonders how the Rosh can can make such a ruling when the Gemara states that a person is believed if he says he meant to say “bread made from wheat” when he in fact said “bread made from barley.” What’s the difference between the two cases?
The Korban Nesanel (to the Rosh, Nedarim, 2:20) answers that a person is only believed when he clarifies his oath immediately after uttering it. The Rosh’s case concerns someone who did not clarify his words until sometime later.