Further, we have seen that he was a Stoic philosopher and as such he was fully aware of the importance of reason and carries through his rational system in a very radical way. But the same Tertullian is also aware of the fact that on the basis of his philosophical attitude there is something else, namely the Christian paradox, He who said that the human soul is naturally Christian (anima naturaliter christiana,) a phrase you should remember, and is the same who is said to have said, at the same time – though he did not actually say it – that “I believe what is absurd,” (credo quia absurdum est). What he really said was: “The Son of God is crucified; it is not a shame because it is a matter of shame. And the Son of God had died; it is credible because it is inadequate And the buried (was) resurrected; it is certain because it is impossible.” Now what you find in such paradox is a mixture of an understanding of the surprising, unexpected – and that means, in Greek, “paradoxical” – -reality of the appearance of God, or God-man unity, under the conditions of existence; and at the same time it is a rhetorical expression of this idea, in the way in which the Roman educated orators used the Latin language. So you must not take it as a literal expression but as a pointing – by means of paradox – to the incredible reality of the appearance of Christ. Now people have added to this, credo quia absurdum est, “1 believe because it is absurd,” but this of course is not Tertullian. He never would have been able to give very clear dogmatic formulas and (be) a Stoic, believing in the ruling power of the Logos.

In Tertullian also appears something which is important later in the West, namely the emphasis on sin. He speaks of the vicium originis, the original vice, and identifies it with sexuality. In this way he anticipates a long development of Roman Christianity, the depreciation of sex and the doctrine of the universality of sinfulness.