A comparative study of Tabatabai and Aquinas's versions of the proof of necessity and possibility

The existence of God is such an important topic that has long preoccupied the human mind. In philosophy of religion, philosophers have tried in different ways to prove the existence of God. The proof of necessity and possibility is one of the cosmological demonstrations which involves proving the existence of God using a posterior approach. In Western philosophy, Thomas Aquinas, influenced by Islamic philosophy, has presented a particular version of this proof. In Islamic philosophy, the proof has been referred to as 'burhan al-siddiqin' (proof of the veracious). One of the scholars who has especially discussed about it is Allamah Tabatabai. His version of this proof can be illustrated through the following points. 1- The objective reality of existence is its true being which lies against fallacy. 2- This reality is what every sentient being must inevitably accept and cannot take in any form of nullity. 3- When a reality cannot be null, it means it is necessary and because reality cannot be mixed with inexistence, it has eternal necessity and everything requires reality if they are to exists. Thus, the necessary existence of God is clear and evident for human beings and the proofs of God's existence function as reminding element. The version of the proof of necessity and possibility presented by Aquinas can be explained as follows: 1- There exist the possible beings (the being which can be existent or non-existent) 2- The possible existents are eternal which means if the entire universe is possible existent, it did not exist at a particular time. 3- If the entire universe were possible existent, it wouldnt exist even now, while it exists now. 4- Thus the whole universe cannot be just possible existent, and it must include a necessary existent as well. 5- Every necessary existent receives its existence either from its own or from others. 6- The necessary existents that receive their existence from others cannot rely on others in an endless manner (infinite regress is invalid) 7- There is a being who is necessary self-existent. In this essay after the analysis and criticism of both versions, the similar and different aspects will be stated, some of which are as follow: 1- In Aquinas's version, God is looked upon as only the creative cause, while in Allamah's version, besides being creative cause, God is considered as continuing cause as well. 2- Aquinas's argument is based upon the philosophical principle of invalidity of infinite regress, also he claims a regress of material causes which is not in fact invalid, while in Allamah's version no philosophical principle is presupposed. It is worth mentioning that in philosophy, the invalidity of regress in causes depends on three requirements: actualization, sequence and unity of existence of all causes, therefore the infinite regress of material causes which lacks the mentioned requirements is not invalid. Also Thomas's version of the proof, although does not concern any divine act or attribute, when it comes to proving the existence of necessary existent, cannot prove His absoluteness. As his argument consists of the concepts such as gradation or multiplicity of existence and… fails to prove the absoluteness of Creator, on the other hand, Allamah Tabatabai's version of the proof, first focuses on proving the absoluteness of God's essence and then considers the necessity as its initial determining quality. Thomas's version presupposes and applies the concepts of necessity and possibility, while in Allamah's version such concepts are not explicitly mentioned and although in his argument, the existents are divided into necessary and possible, the intended meaning is different from that inferred by Aquinas's version