Bittul chametz - "Kol chamira di-vi-reshuti" (4b–7a)

Our journey begins with understanding the core: What is 'Bittul Chametz'? It's not just reciting a formula. Rather, it's a profound halachic-legal act that changes the status of chametz.

Our great Sages, Rashi and Tosafot, offer us two fundamental interpretations of the concept of 'bittul'. Each builds a complete model of halachic understanding.

1. 1Rashi's Model: 'Mental Nullification'. Bittul is an internal, psychological act of removing ownership and significance from the chametz. It makes the chametz 'dust' in the owner's eyes.
2. 2Tosafot's Model: 'Hefker' (Ownerless). Bittul is a legal act of declaring the chametz ownerless, removing it from one's possession and transferring it to the public domain, like any other hefker item.

The difference between Rashi and Tosafot is not merely theoretical. It directly impacts many halachic scenarios. Let's examine three key implications.

1. 1Chametz found on Pesach: If bittul is 'mental nullification' (Rashi), then the chametz is no longer yours, and there is no prohibition of 'it shall not be seen' or 'it shall not be found'. If bittul is 'hefker' (Tosafot), then the chametz is not yours, but there is still a rabbinic prohibition of 'bal yeira'eh' and 'bal yimatze' because it is chametz belonging to another Jew (the public).
2. 2Forgot to declare on Erev Pesach: According to Rashi, if one forgot to declare on Erev Pesach, they can still declare in the morning, as it is an internal act. According to Tosafot, if one forgot to declare on Erev Pesach, their chametz is already forbidden by Torah law under 'bal yeira'eh' and 'bal yimatze', and they cannot declare it ownerless, because a Torah prohibition is not nullified by a late declaration of hefker.
3. 3Non-explicit bittul: Is a mental bittul sufficient? According to Rashi, yes, because the essence is the internal nullification. According to Tosafot, hefker requires an explicit declaration, and therefore a mental bittul alone is insufficient.

We nullify chametz twice: once at night after the search for chametz, and a second time in the morning, before the time when eating chametz becomes forbidden. Why this duplication?

Together, we have built the two central models for bittul chametz: Rashi's 'mental nullification' and Tosafot's 'hefker'. We have seen how each model shapes halacha differently in concrete cases.

The double bittul serves as a multi-layered defense, ensuring that even forgotten chametz or chametz still in use becomes nullified and without halachic status in our possession.