Yiddish "derived from medieval German city dialects ... most closely related to the dialects of Regensburg and Bavaria". It was one of the three languages of the Jewish culture area of Ashkenaz, along with Hebrew and Aramaic. Katz looks at the reconstruction, from later and sometimes incidental sources, of linguistic aspects of Ashkenaz culture pertaining to Yiddish, and at the earliest works in it, which include letters, legal documents, and translations of popular epics from other European vernaculars.
Literacy in Yiddish was associated with women — men were expected to learn Hebrew and perhaps Aramaic and if they read Yiddish it was not so openly, with debate over its appropriateness for prayers — and many early books were sponsored by wealthy women. The first printed Yiddish books were produced by Christians, or converts to Christianity. Popular genres included elaborations and paraphrases of portions of the Hebrew Bible (such as the Tseneréne), collections of romances and legends (such as The Book of Stories), and "lifestyle" books offering ethical and practical advice. Yiddish also had an intimate relationship with Kabbalah and Jewish mysticism, acquiring higher status through being used to propagate their ideas.
Pogroms in Central Europe produced a Jewish migration eastwards to an at the time more sympathetic Polish-Lithuanian commonwealth. Katz examines dialect differences between northern (Litvak) and southern (Polish and Ukrainian) dialects, the rise of Hasidism and in opposition to it of the Lithuanian Misnagdim, and the integration of Yiddish as "the third great language of Jewish spiritual life".
Secularisation following the Enlightenment, most prominently in Germany with figures such as Moses Mendelssohn, encouraged assimilation and dismissed Yiddish as "jargon". The maskilim had "ambitions for modernizing, westernizing, emancipating and secularizing East European Jewry", but to that end some of them (controversially) wrote in Yiddish. This helped contribute to the development of a variety of Yiddish styles and a vibrant secular literature. The nineteenth century saw centres such as Odessa flourish, along with the first Yiddish masters: Alexander Zederbaum, Sholem Aleichem and Y.L. Peretz.
Attitudes to Yiddish evolved alongside new visions of Judaism:
"By the late nineteenth century, Yiddish as a matter of principle (rather than the natural language of a time and place) was becoming characteristic of two different Jewries, one at the extreme cultural right (Ultraorthodoxy with Hasidism included), the other on the far cultural and political left (the secularist and revolutionary movements). Much of what is now regarded as the center (Zionism, moderate assimilation, modern Orthodoxy, and more) developed a distaste for things Yiddish. Yiddish as an idea was the subject of scorching debates as never before."
A single ninety page chapter, the longest in the book, covers the entire 20th century. It touches on the role of Yiddish in the Bund and the socialist movement more generally (highlighting the firebrand Yiddishist, educationist, and revolutionary Esther), on the Chernowitz language conference (a key event in a "messy divorce" with Hebrew, at least among the intelligentsia), on Yivo and the founding of academic "Yiddish studies", and on Yiddish in the new Eastern European republics, among the religious majority, and in a brief Soviet literary flourishing. A pivotal point came with the destruction in the Holocaust of the core Yiddish-speaking populations in Eastern Europe; Katz passes over this quickly, with just a brief look at accusations of quietism. Two long post-war chapters cover Israel, where there was open terrorism by Hebrew fanatics against attempts to set up Yiddish newspapers and schools, and the United States, where Jewish migrants came from the "lowest educational class" and a central role was played by Germanized socialist newspapers.
Looking at the 21st Century and the future, Katz bemoans the disappearance of the last Yiddish masters, the decline of Yiddish schools, and the often low quality of Yiddish at university level, despite something of a boom there. Katz himself clearly identifies with these islands of secular Yiddish, sinking and surviving and revived, but accepts that the future of the language lies with the ultraorthodox, in particular the Hasidim; he considers what that means for the future in terms of dialects, a new literature, and so forth.
And so ends a fascinating story. Words on Fire has some linguistic details, mostly in the earlier chapters, but doesn't assume any knowledge of Yiddish (or of Hebrew script). There are some historical details which may only interest specialists — and Katz sometimes seems to mention figures just to honour them — but most of the material is both broader and more broadly linked, so anyone interested in the history of Judaism, Eastern European language politics, or language history more generally should find plenty in it to chew on.