A Review and Analysis of the Arguments and Criticisms of the “Rule of One” (Qāʿida Al-Wāḥid)

Although the “rule of one” (qāʿida al-wāḥid)” has not been denied by most philosophers, it has been studied and carefully considered by the scholars in terms of its arguments, its scope and the answer to the objections made by the opponents. Some have considered this rule self-evident and needless to argue, but at the same time they have put forward arguments to prove it. The proposed arguments can be divided into two categories: the first category are the arguments that try to prove this rule by relying on the invalidity of applying two concepts to the cause and the second category are the arguments that prove it with regard to the necessity of cognation between cause and effect. Opponents, on the other hand, have raised a number of objections to disprove the principle. Therefore, in this article, first, we will explain and analyze the arguments for the rule, and then deal with some of the criticisms and try to answer to them. As a result, this rule can be proved by the argument which is based on the principle of cognation (in the correct interpretation). According to this argument, the one on the side of cause is the “one in its all aspects” including individual and specific one, and the one on the side of effect refers to the existential one, not the “one in its all aspects”. Thanks to these two, namely the cognation and the fact that the one on the side of effect is not the “one in its all aspects”, most criticisms are rejected.