What is the criterion for distinguishing monotheism or the Unity of God [tawḥīd] from polytheism [shirk]?

Reply: The most important issue in the study of monotheism [tawḥīd] and polytheism [shirk] is discerning what their criterion is, and if this issue is not decisively settled, part of the secondary issues will remain unsolved. Along this line, we shall discuss the issue of monotheism and polytheism in different dimensions albeit in concise manner.

1. The unity of the Divine Essence [dhāt]

The discussion of the unity of the Divine Essence may be in two ways:

a. God, whom scholastic theologians [mutakallimūn] define as the “Necessary Being” [wājib al-wujūd]), is One; He has no partner and nothing can be compared to Him. This meaning of monotheism is the same as that which God mentions in various ways in the Glorious Qur’an, such as: ﴾ شَيْءٌ كَمِثْلِهِ لَيْسَ ﴿ “Nothing is like him.”[1]

Elsewhere, it says: ﴾ أَحَدُ كُفُوًا لّهُ يَكُنْ لَمْ وَ ﴿ “Nor has He any equal.”[2]

Of course sometimes, this kind of monotheism is vulgarly interpreted in another way and more attention is given to the numerical sense of monotheism and that is, God is One and not two.

It is quite obvious that this way of defining monotheism is incompatible with the Divine Station.

b. The Divine Essence is simple and not compound because a being’s being constitution [tarakkub] of mental or external parts indicates that it is in need of its component parts and the “need” implies that there is “possibility” [imkān] and the possibility, in turn, necessarily mean that there is a need for a cause [‘illat],[3] and all these are discordant with the station of the Necessary Being.