Actualitas omnium actuum, perfectio omnium perfectionum

In order to refute the Kantian thesis that being is not a predicate it is not enough to assert that being is one predicate or one perfection among others, but it is necessary to maintain that being is, strictly speaking, the only conceivable perfection, i. e. the one perfection to which any other is reducible: otherwise the chief Kantian misunderstanding is confirmed because we continue to represent being as a univocal notion and to imagine essence as something that has its own meaning before being and apart from it. On the contrary, if we remember the Aristotelian teaching according to which being is not a genus because its differences are within it, we shall be able to work out a proof of the existence of God upon the model of Aquinas' Fourth Way, which is the only proof that Kant did not took into account in his Critique of Pure Reason.