We move from writing to reasoning. Judaic and Islamic law provide not only facts of what must or must not be done. In imposing upon a changing world the enduring principles of justice and truth, each system also appeals to rules of reason, modes of thought that guide people in dealing with the new and the unprecedented. What we now want to know is: do the Judaic and the Muslim lawyer-theologians think along the same lines, follow the same principles of logic, respond to the same types of criticism and challenge? That is what we investigate when we describe, analyze, and interpret the intellectual sources that sustain the law and theology of Judaism and Islam: how does the law intersect with everyday life?
Law codes and traditions form only the starting point in the exposition of the law. They supply facts and principles. But the law carries out its task in the myriad contexts of everyday life—which rarely match in exact detail the facts and principles of tradition. In the processes of reasoning, the doctors of law transform from theory to actuality the received religiolegal systems. At issue in this chapter is the comparison of the rules of rationality that guide Islamic and Judaic jurists in their analysis and exegesis of the law. Do they think or reason in essentially the same ways, or does each find guidance in a special and particular mode of thought, not shared by the other?
The role of reasoning is simple. Faced with a concrete problem, a legal authority undertakes the match between the case and the law that pertains; a process of reasoning will guide him in identifying and applying the governing principles. One familiar rule, deriving from ancient natural history, classifies diverse data within common classes, appealing for evidence to indicative traits of an objective character. Then things are like one another and follow the same rule, or they are unlike one another and follow a different rule. That is one mode of reasoning which extends to the solution of problems of law. Here we take up the way in which the law is turned from heritage and tradition in theory into concrete and palpable, workaday reality: