Anselm's motto, Credo ut intelligam, marks well the distance that has been traversed since Tertullian's Credo quia absurdum est.
The Treatise is a reductio ad absurdum of the principles of Lockianism, inasmuch as these principles, when consistently applied, leave the structure of experience entirely " loosened " (to use Hume's own expression), or cemented together only by the irrational force of custom.
As a human person, I am body and soul; and the idealistic identification of the Ego with soul or mind, involving the corollary that my body belongs to the non-Ego and is no part of myself, is the reductio ad absurdum of idealism.
Credo, quia absurdum was applied, notably by the popular writers of the French Second Empire, in a fashion grotesquely literal enough to scandalize Tertullian himself.
Such a position is a reductio ad absurdum of the attempt to transcend the ultimate character of those intuitions and feelings which prompt men to benevolence.