Written by Yehuda HaChasid, a legendary medieval Jewish sage, Sefer Hasidim is one of the most influential Jewish books of the last thousand years.
In Sefer Hasidim and the Ashkenazic Book in Medieval Europe (University of Pennsylvania Press ISBN 9780812250091), Dr. Ivan Marcus, Professor of Jewish History at Yale University, has written a fascinating monograph that details the story behind this book, the milieu in which it was written, how it was written and updated, and ultimately edited.
Sefer Hasidim is unique in that it is not a commentary on Jewish Law or chumash, rather is it a set of over 1,000 stories about life in medieval Germany.
Marcus observes that we tend superimpose our understanding of authorship, and think that authors write a book in a linear manner, and that it is ultimately preserved in one or more manuscripts.
The style of Sefer Hasidim however, and for that part, much of the written work during the times of early Ashkenazic Europe, was that authors composed books in small-paragraph units, and then combined them over time into different editions.
As such, Marcus contends that Sefer Hasidim was never a single work. Rather it was countless single paragraphs that Yehuda HaChasid combined into sever editions of varying lengths. It was an open work, with numerous parallel edition.
Marcus observes that the writing of Sefer Hasidim was not unique, and was simply the mold in which Ashkenazic books were written during that era. These quick to read, and rearrange paragraphs were later codified into various edition. And in the last part of the book, Marcus has assembled a descriptive catalog of the many manuscripts and editions of Sefer Hasidim.
For those looking to understand the nature of authorship during the era of the rishonim and especially Sefer Hasidim, this is a most interesting read.