It thus becomes clear that the approach they have taken either achieves nothing or involves prolixity and complexity that may be useful for those who engage in sophistry and stubborn opposition, and for those who will accept nothing short of such an argument, as we have pointed out elsewhere.

The substance of their argument is circular reasoning and therefore does not constitute a valid proof. For if one supposes a succession of causes and effects and establishes that this is impossible because what is temporally originated cannot be eternal, it follows that these causes are temporally originated.

He may then be asked: “Why, then, could contingent things not depend on temporally originated causes?”

Following his method, he must say: “What is temporally originated is contingent; what is contingent requires a cause; and its cause cannot be temporally originated.” His argument thus amounts to saying: “What is temporally originated requires an originator because what is temporally originated requires an originator.” For the substance of what he says is: “What is temporally originated must have a cause because it is contingent and therefore requires a determining factor; and its determining factor cannot be temporally originated because what is temporally originated is contingent and must have a cause.”

If he changes the wording and says, “This contingent thing must have a cause, and its cause cannot be contingent because what is contingent must have a cause,” he has merely said: “What is contingent has a cause because what is contingent has a cause.” All of this amounts to proving a proposition by means of itself.