Karo wrote the Shulchan Aruch in his old age, for the benefit of those who did not possess the education necessary to understand the Beth Yosef. The format of this work parallels that adopted by Jacob ben Asher in his Arba'ah Turim, but more concisely; without citing sources. This book, which for centuries was, and essentially still is, "the code" of Rabbinical Judaism for all ritual and legal questions that arose after the destruction of the Temple in Jerusalem, has a remarkable history. The author himself had no very high opinion of the work, remarking that he had written it chiefly for "young students" (Shulchan Aruch, Introduction). He never refers to it in his responsa, but always to the Beth Yosef. The Shulchan Aruch achieved its reputation and popularity not only against the wishes of the author, but, perhaps, through the very scholars who criticized it.
The history of the Shulchan Aruch is, in a way, identical with the history of rabbinical literature of the Jews in Poland for a period of two centuries. Recognition or denial of Karo's authority lay entirely with the Polish Talmudists. German Jewish authorities had been forced to give way to Polish ones as early as the beginning of the sixteenth century.
Karo had already been opposed by several Sephardic contemporaries, Yom-Tob Zahalon, who designated the Shulchan Aruch as a book for "children and ignoramuses" (in his responsa, no. 67, beginning), and Jacob Castro, whose work Erekh ha-Shulchan consists of critical glosses to the Shulchan Aruch. Moses Isserles and Solomon Luria - the Maharshal, were Karo's first important adversaries in Eastern Europe.
Further in response to those who wished to force the rulings of the Shulchan Aruch upon those communities following Rambam, Karo wrote:
- "Who is he whose heart conspires to approach forcing congregations who practice according to the RaMBaM of blessed memory, to go by any one of the early or latter-day Torah authorities?! ... Is it not a case of a fortiori, that regarding the School of Shammai — that the halakhah does not go according to them—they said 'if like the School of Shammai according to their leniencies and their stringencies': The RaMBaM, is the greatest of all the Torah authorities, and all the communities of the Land of Israel and the Arab-controlled lands and the West practice according to his word, and accepted him upon themselves as their Chief Rabbi. Whoever practices according to him with his leniencies and his stringencies, why coerce them to budge from him? And all the more so if also their fathers and forefathers practiced accordingly: for their children are not to turn right or left from the RaMBaM of blessed memory. And even if communities that practice according to the Rosh or other authorities like him became the majority, they cannot coerce the minority of congregations practicing according to the RaMBaM of blessed memory, to practice like they do. And there is no issue here concerning the prohibition against having two courts in the same city, since every congregation should practice according to its original custom…” Similarly, many later halachic authorities predicated the acceptance of the authority of the Shulchan Aruch on the lack of an existing and widely accepted custom to the contrary.
Eventually though, the rulings of the Shulchan Aruch became the accepted standard not only in Europe and the diaspora, but even in the land of Israel where they had previously followed other authorities.
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