Indirectly Violating Shabbat: What Is a Psik Reisha?

Shabbat candles that might rattle when you lean on the table — forbidden, or just uncertain?

Q. Very often, one indirectly causes one of the prohibited “labors” on Shabbat. For example: can I light Shabbat candles on the table when it is quite possible that the table will vibrate while leaning on it, cutting challa, etc?

One of the important rules of Shabbat is that if the undesirable result is inevitable, than it’s called a Psik Reisha and is usually forbidden, but if it may not occur (it’s called “davar she’eino mitkaven”), then it’s fine. Accordingly, if the table is so unstable that every movement will inevitably shake the candles, thus moving the wick closer or further from the oil, it would be prohibited. If it just “may” happen each time you cut challah or lean on it, then it is allowed. Similarly, most people don’t draw blood when they brush their teeth, so only if is someone has gum problems and they inevitably bleed, then it’s forbidden. Almost everyone detaches at least one hair when they comb, so it’s not allowed, but if you use a soft brush, it’s fine. Similarly, the rabbis came out against what some shuls had the custom to pour water on the chazzan when he recited the prayer for rain, because it inevitably launders his clothes, whether he likes it or not. Also, if walking by an electric eye, it activates the lights to go on, it’s prohibited (if it’s not his home, and/or there are security factors, it may sometimes be allowed), yet one is allowed to drag a bench or push a carriage on dirt on Shabbat, because it doesn’t necessarily leave a furrow.