Whether it is necessary that every being be created by God
as such, therefore is it possible for us to find a being uncaused.
Reply to Objection 2: This objection has led some to say that what is necessary has no cause (Phys. viii, text 46). But this is manifestly false in the demonstrative sciences, where necessary principles are the causes of necessary conclusions. And therefore Aristotle says (Metaph. v, text 6), that there are some necessary things which have a cause of their necessity. But the reason why an efficient cause is required is not merely because the effect is not necessary, but because the effect might not be if the cause were not. For this conditional proposition is true, whether the antecedent and consequent be possible or impossible.
Reply to Objection 3: The science of mathematics treats its object as though it were something abstracted mentally, whereas it is not abstract in reality. Now, it is becoming that everything should have an efficient cause in proportion to its being. And so, although the object of mathematics has an efficient cause, still, its relation to that cause is not the reason why it is brought under the consideration of the mathematician, who therefore does not demonstrate that object from its efficient cause.