Karo kept the four-part structure that Jacob ben Asher had devised for the Arba'ah Turim two centuries earlier, and the divisions have organised practical halakhah ever since. Orach Chayim, the Way of Life, follows the daily and yearly round: waking, prayer, blessings, Sabbath and the festivals, the laws a Jew meets every single day.
Yoreh De'ah, It Shall Teach Knowledge, gathers the ritual law that requires learned decision, including the dietary laws of slaughter and mixtures, idolatry, vows, circumcision, conversion, mourning and the honour due to Torah scholars. Even ha-Ezer, the Stone of Help, covers marriage, divorce and the marriage contract. Choshen Mishpat, the Breastplate of Judgment, holds civil and judicial law: courts, testimony, loans, partnership, damages and inheritance.
Within each section the chapters, simanim, are numbered continuously and subdivided into paragraphs, seifim, so that any ruling can be cited in a few characters. The work's genius was compression. Karo had already written the Beit Yosef, an exhaustive survey of every opinion from the Talmud onward, keyed to the Tur; the Shulchan Aruch states only his conclusions, in short declarative Hebrew, a table set with decisions rather than deliberations, intended, as he wrote, to be reviewed regularly until its rulings were fluent.