There are two reasons why I would be concerned regarding using a Swiss Army knife on Shabbat:

  1. Possible violation of a melacha of creating / completing a tool. When you fold out the knife, you are "completing" the use of the tool, as the main part of the unit is the knife handle and the knife now folded out creates its use as a knife.

  2. Muktzah - The unit contains other gadgets that cannot be used on Shabbat such as a screwdriver, scissors, etc.

  3. Borer - selecting - You are selecting / choosing a specific tool from among others in the collection.

Are any of these or possible other items concerns prohibiting using a Swiss Army knife on Shabbat, or are there any leniencies providing one follows certain conditions?

  • 1
    Re 2. At worst, wouldn’t it be a בסיס לדבר האסור ודבר המותר, which one is allowed to move directly in certain scenarios? – DonielF Feb 20 at 16:19

The gemara (Shabbos 47a) explicitly permits reassembling tools that are easily and intentionally taken apart and reassembled as part of their normal use (such as fold-out beds; see also Rambam Hilchos Shabbos 22:26). Also, even a kli shemlachto l'issur (utensil devoted to purposes forbidden on Sabbath) such as a screwdriver, is allowed to be used l'tzorech gufo (for permitted purposes), kol sheken (all the more so) a kli shemlachto l'issur u'lheter (utensil devoted to both permitted and forbidden purposes) such as a pocket knife. (See also Yalkut Yosef 308; http://www.halachos.com/halacha/hal_601_700.asp #677)

  • other than an umbrella as an "ohel" has special extra restrictions (over a "cli") – CashCow Jun 3 '15 at 10:07
  • See latest edit re borer problem. Re, your second sentence, does this mean that I'm allowed to use a scissors to cut parsley or cut open a food bag on Shabbat? – DanF Feb 13 '18 at 20:47

The first question is already answered but you ask for more details on borer and muktze. Overall they do not represent obstacles to using such a knife.

There is no issue of borer when selecting the good from the bad, in this case the tool you want from the others, with the hand, right before use. Shemirat Shabbat KeHilchata (3:27) notes it is permitted to select an article which one wishes to use at present from articles of the same type which come in different sizes or colors and do not all have an identical use.

Regarding muktze, one may move an object (to use it, or for its space) if it is used with equal (or more) frequency for performing both permitted and prohibited activities (Shemirat Shabbat KeHilchata 20:80). This is a kli shemelachto l'issur, see SA OC 308:3 and following.

However note that one should not use these objects if one has available an article whose use is not restricted (SSK 20:8) or for a non-Jew.

I would also note the Shemirat Shabbat KeHilchata (20:81) explicitely discusses a penknife which appears to be similar to a Swiss knife (i.e., a tool with multiple blades, some of which might be useful for a permitted use on Shabbat, others not)

A penknife sometimes has fixed attachments which may not be used on Shabbath, such as scissors or a nail-file. Even if one is particular not to use these attachments for any other than their intended purpose, one may move the penknife in order to use its blade. One must not, however, open those attachments that it is forbidden to use.

  • Yes, this answered my question, hence the bounty. Thank you. You have some "technical" aspects linked in there such as kli shemelachto l'issur. I have to read up on how these concepts work. – DanF Feb 26 at 23:20

1) I don’t imagine completing a Keli is an issue as it is already a fully functional kli and it is its standard mode of use to open and close, much like a foldable stroller or pack and play (sorry I don’t have seforim with me, but see rabbi ribiats book).

2) I believe this was sufficiently answered, as at worst it is a kli shemelochto l’issur which one is allowed to use l’tzorech guffo I.e. for a permitted use.

3) there is certainly no issue of borer if you are choosing the tool that you want (the ochel) for immediate use. Furthermore if each tool is easily identifiable, it may not be viewed as actual mixture.

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