In other words...

In other words: an existent will be either essentially a necessary existent, having necessary existence by itself, or it will be a contingent existent, and such existents only come about when necessitated by a cause, and their existence reaches the level of necessity, that is, it comes to shed the possibility of nonexistence. This premise is both certain and indubitable.

When the attribution of necessity is not required of the essence of an existent, there is no other alternative but that it is brought about by another existent, that is, a complete cause makes the existence of the effect ‘necessary by another’ ( ḍarūrī bil-ghayr ). This premise is also self-evident and indubitable, for every attribution must be in one of two states: by itself ( bil-dhāt ) or by another ( bil-ghayr ). If it is not by itself it must be by another.

Hence, if the attribution of necessity required of any existent is not essential, it must derive from another existent called the cause. Circles and regresses of causes are impossible. This premise is also certain and was explained in Lesson Thirty-Seven.

Given these premises, the argument from contingency may be formulated as follows: the existents of the cosmos are all brought about with the attribution of necessity by another, because, on the one hand, they are contingent existents, and do not have the attribution of necessity essentially (the first premise).

On the other hand, no existent occurs without the attribution of necessity (the second premise), hence, they must be necessary by another, and the existence of each of them is required by a cause (the third premise). Now if we assume that their existences are required by each other, this implies a circle of causes, and if we assume that the chain of causes extends infinitely, this implies an infinite regress of causes. Both of these are invalid and impossible (the fourth premise).

Hence, there is no alternative but to accept that at the head of the chain of causes there is an existent which by itself necessitates existence, that is, which is the Necessary Existent. This demonstration may also be formulated in another version which does not require the fourth premise (the invalidity of the circle and regress), as follows.

For the set of contingents, no matter how imagined, necessity will not be realized in any of them without the existence of the essentially Necessary Existent.