Hot answers tagged rabbeinu-tam
Rabenu Tam (as cited in paragraph 6 of the Rosh's laws of sefer Tora) holds that ink made of gallnuts (which we use even in 'his' t'filin) is no good. Also, Rabenu Tam (as cited in Tosafos to M'nachos 33:1 s.v. "Ha daavida") holds the parchments must be lying flat in their case, and we put them upright (per SA OC 32:45), and even in 'his' t'filin.
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.
In addition Rabeinu Tam holds (see Bais Yosef (3rd from top)) that the word Letotofos in the Parsha Vehaya Im Shomo'a is written without any Vov while we write it with a Vov after the first Tes even in Rabeinu Tam's Tefillin.
The main difference between them is the order of the passages: whether "Sh'ma" appears before (Rashi) or after (Rabenu Tam) "V'haya im shamoa". An additional difference is that, in the head t'fila, the parchment containing "V'haya im shamoa" is wrapped in a hair that sticks out the front of the t'fila, and where that sticks out identifies at a glance the ...
This is Asur because it goes under the category "Maalim BikDusha WeLo Moridin." (Od Yosef Hai Wayera #8. see Oserot Yosef 3:6).
No. Anyone who wears Rabbeinu Tam תפילין wears Rashi תפילין as well. This is because doing so would be saying that Rashi is wrong, which is not something anybody is on the level to do in this generation. The Shulchan Aruch says that wearing Rashi's תפילין is the accepted minhag, and only a very pious person should also wear Rabbeinu Tam's (ש"ע א"ח 34:1). ...
The Aruch Hashulchan that you refer to, clearly explains that nowadays you cannot wear Rabbeinu Tam Tefilin exclusively. He admits that in very early times there was an argument, but then demonstrates how we Pasken like Rashi. ופלא שהרא"ש והטור וכמה מראשונים סבירא להו דרב האי פסק כרבינו תם, והרמב"ם כתב שפתחו תפליו ואינו כן. ובמרדכי וכן בשארי ראשונים ...
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