Why there can be only one God

Tawhid, the oneness of God, is the heart of Islamic belief. This paper argues that the Qur'an does not only proclaim it but points to reasons for it, and that classical Muslim philosophers and theologians turned those reasons into careful rational arguments.

The starting point is the Qur'an: “Had there been within them [the heavens and the earth] other gods besides Allah, they both would have been ruined” (21:22). Another verse, 23:91, says that each god would have taken away what he created and some would have tried to overcome others. Kalam theologians, who defended belief through rational argument, developed this into the proof from mutual hindrance (burhan al-tamanu'). Al-Juwayni and al-Ghazali asked what would happen if two all-powerful gods willed opposite things, one wanting an object to move and the other wanting it to stay still. Both wills cannot be carried out; if neither is, both are powerless; if only one is, the other is not truly God. Fakhr al-Din al-Razi added that even two gods who always agreed would each depend on the other's agreement.

The paper sets out further arguments. Ibn Sina (Avicenna) reasoned from contingent things, which could have failed to exist, to a Necessary Existent, and argued that two necessary beings would have to differ in some way, which would limit them. The paper links this to al-Samad in Surah al-Ikhlas (112:2), the Self-Sufficient on whom all depend. Maturidi and Ash'ari scholars argued that God has no parts, since anything made of parts depends on them. A redundancy argument asks what work a second god would do if one is all-powerful. The unified order of the cosmos, one set of laws from galaxies to atoms, is read as the work of one will. The paper also outlines Mulla Sadra's view of the unity of existence, noting that it has been widely rejected by Sunni theologians.

The authors conclude that revelation and reason converge: whether one starts from the order of nature, from logic or from metaphysics, the answer is the same. They add that modern philosophers asking whether there could be more than one almighty being have reached conclusions consistent with these classical proofs.