Of special significance are the lengthy introductions he included in his commentary. The general introduction which heads his commentary to the order of Zera'im is in reality an introduction to and history of the Oral Law from Moses until his own days. The introduction to Avot, known as the Shemonah Perakim ("Eight Chapters") is a philosophical and ethical treatise in which its author harmonized Aristotle's ethics with rabbinical teachings. In the introduction to Mishnah Sanhedrin (10:1), which begins with the words "All Israel has a portion in the world to come," Maimonides dealt at length with the fundamental doctrines of Judaism which are formulated in the Thirteen Articles of Faith . Especially extensive and exhaustive is the introduction to the difficult order Tohorot, in which Maimonides systematizes all that had been said in talmudic literature on the subject of ritual purity and impurity.