Avicenna and Mulla Sadra’s Solutions for the Problem of the ‘Single Essence under Two Categories’

To solve the problem of mental existence, Avicenna emphasized that the definition of substance is that its external existence (fi al-aʿyān) does not need a subject. The mentioned definition applies to both mental and external substances. He concluded by adding ‘its external existence is not in a subject’ to the definition of substance that, on the one hand, the same meaning is reflected in the mental existence of the substance and, on the other hand, the same mental substance is a quality of the soul, that is an accident; so that the problem of ‘single essence under two categories’ will not occur. Mulla Sadra put forward two responses to the problem of mental existence. The first one was based on the theory of the earliest philosophers and the acceptance of incarnate dependence, because of which it would be consistent with Avicenna’s opinion. However, Mulla Sadra said that Avicenna, by adding the ‘fi al-aʿyān’ to the definition of substance, had confined the substantiality to individual substances, which requires the opposition between reality and mentality. Mulla Sadra’s second response is based on the emanative dependence in which the mental existence is considered a product of the soul, in which case, the problem of single essence under two categories will not occur in the first place. This view cannot be reconciled with Avicenna’s solution which is based on incarnate dependence. A Careful look at Avicenna’s statements, however, will show that Mulla Sadra’s criticism of him may be defended by making some qualifications and explanations so that we find out that Avicenna’s analysis had prepared the ground for Mulla Sadra’s first response to the problem by distinguishing tautological predication and common technical predication.