The belief in reason, as well as some of the tenets of Muʿtazilite theology, were taken over by Saʿadia ben Joseph (882–942), who was also influenced (either directly or through the intermediary of an Arabic philosopher) by John Philoponus (6th century), a Christian philosopher who argued against certain Aristotelian and Neoplatonic positions. Saʿadia’s main theological work, Kitāb al-amānāt wa al-iʿtiqādāt (Beliefs and Opinions), is modeled on similar Muʿtazilite treatises and on the Muʿtazilite classification of theological subject matter known as the Five Principles.
Like many Muʿtazilite authors, Saʿadia set forth in his introduction a list and theory of the various sources of knowledge. He distinguished four sources: (1) the five senses, (2) the intellect, or reason, (3) necessary inferences, and (4) reliable information given by trustworthy persons. In Saʿadia’s sense of the word, intellect, or reason (al-ʿaql), is an immediate, a priori cognition, independent of sense experience. In Beliefs and Opinions the intellect is characterized as having immediate ethical cognitions—that is, as discerning what is good and what is evil—in opposition to the medieval Aristotelians, who did not regard even the most general ethical rules as knowable a priori. The third source of knowledge comprises inferences of the type “if there is smoke, there is fire,” which are based on data furnished by the first two sources of knowledge. The fourth source of knowledge is meant to validate the teachings of Scripture and of the religious tradition, which must be regarded as true because of the trustworthiness of the men who propounded them. One of the work’s main purposes was to show that the knowledge deriving from the fourth source concords with that discovered by means of the other three—i.e., that religion and human reason agree.
Saʿadia opposed Aristotle’s view that the natural order was eternal. He held, with other partisans of the Muʿtazilite kalām, that the demonstration of the temporal creation of the world must precede and pave the way for the proof of the existence of God the Creator. Given the demonstrated truth that the world has a beginning in time, it can be proved that it could have been produced only through the action of a creator. It can further be proved that there must have been only one creator.
The theology of Saʿadia, like that of the Muʿtazilites, hinges on two principles: the unity of God and the principle of justice. The latter takes issue with the view (widespread in Islam and present also in Judaism) that the definition of what is just and what is good depends solely on God’s will, to which none of the moral criteria found among human beings are applicable. According to this view, a revelation from God can convert an action generally recognized as evil into a good action. Against this way of thinking, Saʿadia and the Muʿtazilites believed that being good and just or being evil and unjust are intrinsic characteristics of human actions and cannot be changed by divine decree. The notions of justice and of good, as conceived by humans, are binding even on God himself. Indeed, the ethical cognitions of humans are the same as those of the Deity.
Saʿadia also addressed the issue of the function of religious law. Of central importance in traditional Judaism and Islam, the law was thought to have been established to compel humans to perform good actions and avoid bad ones. Because Saʿadia believed that humans have a priori knowledge of good and evil and that this knowledge coincides with the principles underlying the most important portions of the revealed law, he was forced to ask whether this law is not superfluous. He could, however, point out that, whereas the human intellect recognizes that certain actions—for instance, murder or theft—are evil, it cannot by itself discover the best definition of what constitutes a particular transgression; nor can it, on its own, determine an appropriate punishment. On both points, Saʿadia asserted, the commandments of religious law give the best possible answers.
Saʿadia called the commandments that accord with the behests of the human intellect the intellectual, or rational, commandments. According to him, they include the duty of manifesting gratitude to the Creator for the benefits he has bestowed upon humans. Saʿadia recognized that a considerable number of commandments—for instance, those dealing with the prohibition of work on the Sabbath—do not belong to this category. He held, however, that the obligation to obey them can be derived from the rational commandment that humans must be grateful to God, for such gratitude entails obedience to his orders. The Karaites
Saʿadia’s adoption of the rational Muʿtazilite theology was a part of his overall effort to consolidate rabbinical Judaism (based on the Mishna and Talmud), which was being attacked by the Karaites. This Jewish sect, founded by Anan ben David in the 8th century, rejected the authority of the Oral Law and the commentaries on it—that is, of the Mishna and the Talmud. In the 10th century and afterward, the Karaites accepted as their guides the Hebrew Bible and human reason, in the Muʿtazilite sense of the word. Their repudiation of postbiblical Jewish religious tradition facilitated a rational approach to theological doctrine. This approach led Karaite authors to criticize the adherents of rabbinical Judaism for holding anthropomorphic beliefs based in part on texts of the Talmudic period. Karaite authors propounded, in conceptual terms, a theology of Jewish history in exile (galut). Life in exile is a diminished existence; nevertheless, the good or bad actions of the Jewish people (rather than their material strength or weakness) affect the course of history. Redemption may come when all Jews are converted to Karaism.
The Karaites adopted Muʿtazilite kalām wholesale, including its atomism. The Muʿtazilite atomists held that everything that exists consists of minute, discrete parts. This applies not only to bodies but also to space, time, motion, and the “accidents”—that is, qualities, such as colour—which the Islamic and Jewish atomists regarded as being joined to the corporeal atoms but not determined by them, as had been believed by the Greek atomists. An instant of time or a unit of motion does not continue the preceding instant or unit. All apparent processes are discontinuous, and there are causal connections between their successive units of change. The fact that cotton put into fire generally burns does not mean that fire is a cause of burning; rather, it may be explained as a “habit” that has no character of necessity. God’s free will is the only agent of everything that occurs, with the exception of one category—human actions. These are causes that produce effects; for instance, one who throws a stone at someone else, who is then killed, directly brings about the latter’s death. This inconsistency on the part of the theologians was required by the principle of justice, for it would be unjust to punish someone for a murder that was a result not of this person’s action but of God’s. This grudging admission that causality exists in certain strictly defined and circumscribed cases was occasioned by moral, not physical, considerations. Jewish Neoplatonism Isaac Israeli
Outside Babylonia, philosophical studies were pursued by Jews in the 9th and 10th centuries in Egypt and in the Maghrib (northwest Africa), most notably by Isaac ben Solomon Israeli (832/855–932/955), an Egyptian-born North African who has been called “the first Jewish Neoplatonist.” In his philosophical works, such as the Kitab al-ustuqusat (“Book of Elements”) and the Kitab al-hudud (“Book of Definitions”), Israeli drew largely upon a 9th-century Muslim popularizer of Greek philosophy, Abū ğūsuf Yaʿqūb al-Kindī, and also, in all probability, upon a lost pseudo-Aristotelian text. The peculiar form of Neoplatonic doctrine that seems to have been set forth in this text had, directly and indirectly, a considerable influence on medieval Jewish philosophy.