 Nevertheless, R. Ishmael's 13 principles are perhaps the ones most widely known; they constitute an important, and one of Judaism's earliest, contributions to logic, hermeneutics, and jurisprudence.Judah Hadassi incorporated Ishmael's principles into Karaite Judaism in the 12th century.Today R. Ishmael's 13 principles are incorporated into the Jewish prayer book to be read by observant Jews on a daily basis.