Saadia (above p. 28) puts revelation as a fourth source of truth parallel to sense, judgment and logical inference. To be sure he, in one instance (p. 35), speaks of the reason as preceding the Bible even as tradition follows it, but this is only a passing observation, and is properly corrected by the view expressed elsewhere (p. 28) that while a Jew is not forbidden to speculate, he must not set the Bible aside and adopt opinions as they occur to him. Al-Basir does not leave the matter in this unsettled condition. He definitely gives priority--logical priority, to reason. Knowledge, he says, must precede revelation. The prophet as the messenger of God cannot be believed on his word, for the opponent may have the same claim. Not only must the prophet authenticate his mission by the performance of a miracle which cannot be explained by natural means, but we must know besides that he who sent him has our good at heart and would not deceive us. A knowledge of the existence, power and wisdom of the creator must therefore precede our belief in the prophet's mission. To take these truths from the words of the prophet and then give him credence because God sent him would be reasoning in a circle. The minimum of knowledge therefore which is indispensable before we can make any appeal to the words of the prophet is rational proof of the existence, power and wisdom of God. Having this minimum the person who is not practiced in speculative investigation may rely for the rest of the creed, for example, the unity of God and his other attributes, upon the words of the Bible. For if we know independently that God is Omnipotent and Omniscient, and the prophet can substantiate his claim to be a divine messenger by the performance of genuine miracles, his reliability is established and we are safe in accepting all that he has to say without proof; but the fundamental thing to do is to establish the prophet's reliability, and for this an independent source of evidence is necessary. This is the reason.