Beitzah 12 - Once it is allowed - it is allowed

Thirty-nine labors are prohibited on Shabbat, and they are equally prohibited on a Holiday (Yom Tov). However, on Yom Tov, one can cook food, and the work needed for this constitutes an exception to the thirty-nine labors rule.

Beit Shammai states that one cannot carry a child or a Torah into the street on a Yom Tov. Why not? Because they are not edibles. Beit Hillel allows this. We thus see that Beit Hillel has a rule: once something is permitted for the purposes of cooking, it is permitted for all purposes. But how do we know that this is a general argument and not just one about carrying? They also disagree about lighting the fire: once it is allowed for cooking, Beit Hillel permits it for all other purposes.

When one cooks, she needs to give a portion to a Kohen. Beit Shammai prohibited carrying presents to the Kohen: just as one cannot carry the tithe to Kohen on a Yom Tov, so she cannot take other gifts. What does Beit Hillel answer? They say that it is not the same: tithe cannot be carried because it cannot be separated; will you say the same about Kohen food gifts, which can be separated? - Of course not.

Art: Girl Carrying a Child by William-Adolphe Bouguereau