Tosafists

Tosafists were medieval rabbis from France and Germany who are among those known in Talmudical scholarship as Rishonim (there were Rishonim in Spain also) who created critical and explanatory glosses (questions, notes, interpretations, rulings and sources) on the Talmud. These were collectively called Tosafot ("additions"), because they were additions on the commentary of Rashi. The Tosafists lived from the 12th century to the middle of the 15th century and the Tosafot are a compilation of the questions, answers and opinions of those rabbis. The Tosafot are very important to the practical application of Jewish law because the law will differ depending on how the Talmud is understood and interpreted.

Each generation of the Tosafists would add to those compilations and therefore there are many different versions of the Tosafos. In addition each compilation of the Tosafos did not contain everything that was said by the Tosafists on the subject so compilations will differ in what they say. For this reason some things that were said by the Tosafists will be found only in obscure versions of the Tosafos.

The final version of these commentaries was published on the outer side of the Soncino edition of the Talmud, printed in Soncino, Italy (16th century), and was the first printed edition of the full Talmud. The publisher of that edition was a nephew of Rabbi Moshe of Spires (Shapiro) who was of the last generation of Tosafists and who initiated a project of writing a final compilation of the Tosafos. Before he published his Talmud he traveled throughout France to the schools where the Tosafists learned and gathered all of the different manuscripts of that final version of the Tosafos and printed them in his Talmud. Since then every publication of the Talmud was printed with the Tosafos on the outer side of the page (the inner side has the commentary of Rashi) and is an integral part of the study of the Talmud.

During the period of the Tosafists the church enacted a law that prohibited possession of the Talmud under pain of death and 24 wagon loads of scrolls of the Talmud were gathered from all of France and burned in the center of Paris. The intention of the church was that the study of the Talmud should be forgotten and once forgotten it would remain forgotten for all generations since there would be nobody to teach it. As a result, the Tosafists devised a system where they could study the Talmud without the existence of a text despite the vastness of the Talmud. They appointed scholars, each to be expert in one the volumes of the Talmud, to know it by heart and very well, and so through these scholars they would have expertise and knowledge in all of the Talmud. As they would study a particular text in one volume of the Talmud those scholars who were expert in different volumes of the Talmud would tell of anything in the volume of the Talmud that they were expert on that would contradict their understanding of the text at hand. Thus an important aspect of the scholarship of the Tosafists is to use texts in different areas of the Talmud to disprove certain interpretations of the Talmud (often those of Rashi) and to determine the correct way to understand the Talmud.

...
Wikipedia