The law goes out of the yeshiva and into the house

Before this, a code of law was written for someone who had already studied. Rabbi Joseph Karo's Shulchan Aruch is a book for a rabbi: it gives the ruling but assumes the reader knows where it came from. An ordinary man asked his rabbi, and that was the only way to learn what to do.

In the nineteenth century this stopped working. Communities grew and scattered, printing grew cheap, the literate grew more numerous and the rabbis fewer per head. And then the law began to be written differently.

The first was Rabbi Avraham Danzig, a Vilna merchant who lost his business in a powder-magazine explosion and became a dayan. Chayei Adam is 224 chapters of Orach Chaim retold for the literate layman, with Nishmat Adam beside it—the same matter taken deeper, so that the abridgement can account for itself. In town after town chevrot Chayei Adam were formed: people learned the law together, without a yeshiva.

Sixty-odd years later Rabbi Shlomo Ganzfried published at Ungvár the Kitzur Shulchan Aruch—the whole Shulchan Aruch in one book in plain Hebrew. It spread as almost no other Jewish book of modern times: in Hebrew, in Yiddish, house after house.

The other side must be said too. In abridging one must choose among opinions, and Ganzfried chose the stringent, Hungarian ones. The Kitzur is not a smaller Shulchan Aruch but a code with a face of its own, and later decisors note it.

From here the road forks. The Chafetz Chaim in the Mishnah Berurah carries the 'what to do' design to its end; Rabbi Yechiel Michel Epstein in the Aruch ha-Shulchan goes the other way—from the Talmud to the ruling, explaining why it is ruled so. Both books appear almost together, at the end of that same century.