Being oppositional to natural theology is a hallmark of Karl Barth’s theological posture. His primary rejection of a natural theology isn’t a result of his socio-politico atmosphere in the Reich of Germany per se; even though it has application towards the type of Nationalistic Socialism that characterized Adolf Hitler’s vision of the golden age of Germany. Barth rejected natural theology for theological reasons; i.e., theological-anthropological reasons. He maintained a radical commitment to the reformational notion of the total depravity of humanity; albeit, in an Athanasian key. This commitment is best illustrated by his collegial correspondences, and even debates with Catholic German theologian, Erich Przywara. Przywara, was a modern advocate, and constructive builder, indeed, a retriever of the classical Thomistic analogia entis (‘analogy of being’). Przywara ultimately argued from something like a capaciousness left in fallen humanity, as if a residual spark continued to burn within the intellect; which when perfected by grace, even preveniently or objectively so, would allow fallen human beings to build an intellectual cathedral wherein its spire might reach into the heavens and touch the feet of God. But of course, this was a speculative measure by which human beings reason by a series of negations from their finite beings to its primary and first cause in the infinite being, the unmoved mover, who is, in the Przywaran frame, the God of Jesus Christ. Barth retorted to such machination with a loud Nein, such that the canton church bells in Basel were made to ring out.

Barth offered his own reading on thinking God. This has been identified by such theologians as Eberhard Juengal et al. as the analogia fidei -/relationis (analogy of faith -/relation). Barth contended that there was such a qualitative disjunction between God and humanity that outwith God’s invasion, His descending into the fallen world, outwith His assumptio carnis (assumption of flesh) it would be nigh impossible for human beings to begin to even imagine the living and triune God; let alone ‘know’ this God. What was required in Barth’s estimation was that God enter into the garb of our humanity, by becoming human Himself in Jesus Christ, and to do so unto the point of death; even death on the cross. Barth maintains that it was only this type of the dissolution of fallen humanity, and then via its resurrection in the resurrection of Jesus Christ, that humanity by the Holy Spirit, in union with Christ’s humanity (spiritually), might come to have a correspondence of faith, with Christ’s faith, through Christ’s relationship to humanity mediated through His humanity, and in turn, through His human nature in inseparable relationship with the divine Logos, who is the ground of Christ’s singular person, that humanity could ever have a center in God to rightly know God by.

With the aforementioned noted, Anthony Feneuil offers a helpful reading on how Barth engaged with Anselm’s so-called ‘ontological proof’ for the existence of God. As Feneuil shows, Barth could affirm Anselm’s proof without collapsing it into something like the analogia entis presented by Przywara et al. So, how could Barth affirm a ‘proof’ for God’s existence, without falling prey to his own critique of an analogia entis (which is a subset of a natural theology simplicter)? Feneuil writes (in extenso):

According to Barth, Anselm’s proof is not natural theology. Anselm never places himself on the —supposedly common to the believer and the unbeliever—ground of natural reason. The definition of God Anselm gives at the beginning of the Proslogion is not, says Barth, a definition in the strict sense of the term but, rather, a confession of faith. It does not define the nature of God but acknowledges a divine command, actually the first of the Ten Commandments (“You shall have no other gods before me”): “We believe that You are something than which nothing greater can be thought.” It is not about the abstract essence of God, but about the relation of lordliness between the revealed God and God’s creatures. Anselm does not place himself on the fool’s ground, he does not think on the same level. And the proof does not primarily prove the existence of God but, rather, the fact that, on the ground of this lordliness relationship that God initiated, it is not even possible for us to imagine, even as a mere hypothesis, the inexistence of God. The mere hypothesis of the nonexistence does not fit God. In that respect as well, God is very different  from any other object of the world (very different from a hundred–euro note, for instance). Therefore, Anselm’s proof is not an ontological proof, that is, a proof that would go from God’s essence in thought of God’s actual existence. It is not a proof in which human thought is above God, in which human thought decides about God’s existence. It is the other way around: the proof aims at showing, from the revealed name of God, that human thought cannot establish itself as a spectator above God. The proof shows that human thought, in relation to God, is unescapably limited.

Therefore, one could say that, in a sense, the proof aims precisely at negating the possibility of any natural theology, understood as a human attempt to escape the relation of obedience to God, and to establish oneself in the position of being able to make judgments about God’s existence, just as about the existence of any object. It is a proof that declares our wisdom as a folly before God. Hence, the insipiens, in Barth’s reading of Anselm—that is, the one who does not understand the proof—is not only the one who denies the existence of God, but also the one who tries to establish this existence on purely rational grounds. Who, then, is the insipiens? He is Descartes, not less than Kant, because when Descartes attempts to ground the certainty of God’s existence exclusively on human reason, he believes that he can consider God as a thought object similar to others, whose existence can always be put into bracket. Insofar, he is an insipiens: he believes that one can talk about God as about a thing or an absent person, using a third-person discourse, whereas one cannot talk about God without talking to God. Consequently, there is no fundamental difference between Anselm’s insipiens and Paul’s fool: both refer to those who do not acknowledge the foolishness of their own wisdom, but neither Anselm’s incipiens [sic.] nor Paul’s fool refer to the one who cannot reason well, for any contingent cause.[1]

If Feneuil is correct in his reading of Barth, and there is no reason to think otherwise, we can see, even in Barth’s reading on Anselm’s ‘proof’ how Barth’s rejection of a natural theology was operative. Ultimately, I would contend, Barth sees natural theology, and its subset in the analogia entis, as foolish because it attempts to decenter God’s ontology with fallen humanity’s; i.e., by asserting that there remains a residual foundation within the intellect of fallen humanity whereby knowledge of the true and living God has been retained; even if it might need a drop of God’s created grace to jumpstart it.

[1] Anthony Feneuil, “The Cross of Wisdom: Ambiguities in Turning Down Apologetics (Paul, Anselm, Barth),” in Christophe Chalamet and Hans–Christoph Askani, eds., The Wisdom and Foolishness of God: First Corinthians 1—2 In Theological Exploration (Minneapolis: Fortress Press, 2015), 174–75.