Alongside the Guide of the Perplexed, Maimonides made a second and in some ways more disruptive rationalist intervention: he tried to fix Judaism's creed. In his commentary on the Mishnah's tractate Sanhedrin, in the section known as Perek Chelek, he set out thirteen principles he argued every Jew was obligated to affirm, the existence and unity of God, the rejection of divine corporeality, the eternity of the Torah, reward and punishment, the coming of the messiah and the resurrection of the dead among them, presented as necessary beliefs in something close to the Aristotelian sense, truths a rational person is compelled to hold once the premises are understood.
The attempt was controversial precisely because Judaism had never had an official creed of that kind, and critics, medieval and modern, have argued that turning belief into an enumerated list borrowed a category from Aristotelian philosophy that rabbinic Judaism had gotten along without for a thousand years, privileging correct belief over correct practice in a tradition usually read the other way around. The controversy never fully resolved the question of whether the principles bind or merely describe Maimonides' own considered view, but the list outlived the argument: reworked into rhymed liturgical form as the hymn Yigdal, probably in the fourteenth century, it is still sung in synagogues today, a philosopher's attempt at systematic theology surviving in popular memory as a piece of music rather than as the argument that produced it.