P'sik reisha - inevitable result without intent

Let's build the foundation for understanding a core principle in Shabbat law: 'P'sik Reisha'. This describes a situation where a forbidden action is an inevitable outcome, even if we didn't directly intend it.

The Gemara lays a cornerstone here: if the outcome of a certain action is inevitable, the action is forbidden by Torah law, even if the person did not intend that forbidden result. Intent for the outcome is irrelevant when the outcome is unavoidable.

Let's sharpen the distinction between two types of P'sik Reisha, which affect the severity of the prohibition. The Gemara differentiates between a situation where the forbidden outcome is 'convenient for him' and one where it is 'not convenient for him'.

1. 1P'sik Reisha D'Niha Lei: The forbidden outcome, while not the primary intention, is beneficial or desired by the person. In this case, all agree the prohibition is by Torah law.
2. 2P'sik Reisha D'Lo Niha Lei: The forbidden outcome is undesired by the person, and may even be harmful or inconvenient. Here, a dispute arises among the Rishonim regarding the severity of the prohibition.

Let's delve into the central dispute among the Rishonim regarding P'sik Reisha D'Lo Niha Lei, and see how it manifests in practical cases.

Examples for application:

1. Opening an old refrigerator with a light: The light will certainly turn on. If the person wants the light (e.g., to see what's inside) – this is P'sik Reisha D'Niha Lei and forbidden by Torah law (the melakha of lighting a fire). If the person doesn't want the light, but just wants to take food, and the light bothers him – this is P'sik Reisha D'Lo Niha Lei, and forbidden rabbinically according to Tosafot.

2. Closing a door on an ant: If the ant will certainly die, and the person has no interest in its death – this is P'sik Reisha D'Lo Niha Lei (the melakha of striking with a hammer or taking a life).

Let's examine another example and understand the implication of 'shiur melakha' on the law of P'sik Reisha.

3. Sitting on an electric chair on Shabbat: If the chair will certainly activate, and the person has no interest in its activation but only in sitting – this is P'sik Reisha D'Lo Niha Lei. But here there's an additional consideration: Does activating the chair even constitute a 'melakha' of its required measure? If not, the prohibition might be lighter, or non-existent.