Tim Garrett on Tertullian and Reason"Faith and Reason: Friends or Foes?" (Probe Ministries: 1998).
Contemporary theologians who deny the rationality of Christian belief often quote Tertullian’s statement that the crucifixion should be believed because it is absurd. He also said the fact of the Resurrection is certain because it is impossible. But these statements must be understood from the context of Tertullian’s own life and work. He himself utilized elements of Greek philosophy and logic that he believed to be compatible with Christian belief. The major emphasis in his writings was to contrast the coherence of Christianity with the inconsistency of his heretical opponents. When he does speak of the absurdity of Christian belief, he is actually referring to the unlikelihood that any human mind could conceive of God’s redemptive plan. Like C. S. Lewis, he was convinced of the truth of the gospel by the very fact that no human being could possibly concoct such a story as is presented in Scripture. Certainly the Jews could not; the claim of Christ that He was God in the flesh was blasphemous to many of them. Nor could the Greeks create such a story; for them, the material world was inferior to the divine realm. God could not possibly assume human flesh in their philosophical reasoning. But for Tertullian, this was compelling evidence that the gospel is true! The religious and philosophical systems contemporary with the advent of Christianity would have prevented any human from simply making up such a fantastic tale. He concluded that the gospel had to originate in the mind of God himself.