 This choice of texts shows that the Ikhwân conform to the “old” tradition that restricted research to the first Books of the Organon, not to that of their great contemporary al-Fârâbî, who expanded it to the whole logical corpus. This might be due to the religious aims of the encyclopedia. Religious matters can only be treated by relying on the sound (sahîh) method for knowledge, while procedures aiming at mere persuasion or linked to the attainment of that which is useful (and not true) are not to be employed. Logic is no longer a simple instrument of science as it was for Aristotle, but a true science, perhaps the most important one. The Brethren call it “the scale of sciences” through which the wise men are able to discern “true from false in speeches, right from wrong in opinions, truth from vanity in beliefs and good from evil in acts” (cf., e.g., Epistle 7, I, 268, 14–16).