My question refers to the class of permitted actions that may inadvertently cause melachas as byproducts. (For example, with hair brushing, the intention is not to pull out the hair, but this does often occur by accident; thus the melacha of shearing is performed inadvertently.)

I had thought that such actions were permitted on Shabbos so long as a byproduct melacha was not inevitable, and that in cases where the melacha is inevitable--such as hair brushing--the action is prohibited.

However, I have encountered one source that says, rather confusingly, "The halacha is that a dvar sheina mitchaven is completely permitted." Does this mean that dvar sheina mitchaven is permitted even if a resulting melacha is inevitable, and is that correct?

  • Related: judaism.stackexchange.com/questions/28904/… – SAH Aug 20 '14 at 16:21
  • I think I learned a better approach to this question: If a melacha is non-inevitable AND it's not your intention to do the melacha /get the result of the melacha, you can do the thing – SAH Jul 20 '17 at 3:45

An excerpt from the source you linked:

Dvar sheina mitchaven: Doing a permitted action in a way in which one doesn’t intend for a melacha to occur as a byproduct of one’s intended action is considered a dvar sheina mitchaven. Nonetheless, when it is inevitable that amelacha will take place as a result of one’s inherently permissible action, that action becomes forbidden (see Pesik Reisha). For example, dragging a light chair in a field where one’s intent is to transport the chair would be a dvar sheinamitchaven when the furrow is created as one did not intend to create a furrow.7 Tosfot (Shabbos 75a s.v. mitasek) writesthat dvar sheina mitchaven is not unique to Shabbos; rather, it is a general exemption found in numerous laws throughoutthe Torah. There is a dispute between Rabbi Yehuda and Rabbi Shimon whether performing an action that is a dvar sheinamitchaven is permitted or forbidden. Within the opinion that is forbidden, many assume that it is only a rabbinicprohibition on Shabbos.8 The halacha is that a dvar sheina mitchaven is completely permitted.9

When it is inevitable, it is no longer termed a "dvar sheina mitchaven" and enters a category called "pesik reisha" which is prohibited. A "regular" dvar sheina mitchaven" is permitted.

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  • Just beat me to it. – Scimonster Aug 20 '14 at 13:40
  • @Scimonster fastest gun in the west. :-) (not really - I'm usually pretty slow) – Y     e     z Aug 20 '14 at 13:41
  • Yup, that's why i don't have another 500 rep on SO... – Scimonster Aug 20 '14 at 13:43
  • Thanks to both of you... I did read that part of the source, but needed your last comment to clarify. – SAH Aug 20 '14 at 13:43

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