If I find a Rabeynu Tam Tefillin and I do not have another one, can I take it apart, and change the rosh (I know how to) from Rabeynu Tam to a Rashi Tefillin?

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    – Isaac Moses
    May 30, 2011 at 14:19
  • 4
    Are you asking whether it is legal or whether it is physically possible/feasible?
    – WAF
    May 30, 2011 at 15:46
  • @Danny Any reason to capitalise "Tefillin"? May 31, 2018 at 11:01

2 Answers 2


You are not allowed to. This is because the two opinions mutually invalidate one another and therefore you would be taking Kosher Tefillin and making it not Kosher according to Rabbeinu Tam. This is considered to be Mezalzel in the shita of Rabbeinu Tam. See the Ridvaz Chelek-6 Siman 2286.

  • The Ridvaz says he first ruled it was permissible, then had a bad dream so he changed his mind. Weird. IAE this would only seem to apply to someone who treats RT's opinion as not nidche lehalacha.
    – Double AA
    Feb 14, 2013 at 5:00

This is Asur because it goes under the category "Maalim BikDusha WeLo Moridin." (Od Yosef Hai Wayera #8. see Oserot Yosef 3:6).

  • Your answer is unclear. Are you stating that the temporary posul status when the tefilla is disassembled is a yerida? Or that Rashi tefillin are somehow "less kadosh" than RT? Jun 30, 2015 at 20:54

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