Here at the blog I haven’t been short on pointing out Karl Barth’s disdain for natural theology and the analogia entis; and truly he did have disdain. But he also saw a proper place for philosophy; not a ‘half-baked’ philosophy (or theology), but a philosophy that truly sought to think ‘under the sun’ as it were. If we were to borrow John Hick’s thinking on correlationist versus non-correlationist theologies we could say that Barth does indeed, even within the theological enterprise, see ‘correlation’ or ‘correspondence’ between genuine philosophy and Christian theology; but only in a qualified sense (of course!). He sees, just as with the secular, philosophy producing the type of proper existential crisis that should attend any type of thought that is purely horizontal and abstracted from thinking human life apart from God. So the correspondence between philosophy and Christian theology for Barth has to do with the role philosophy can play in expressing the condition of the human location in the world apart from Christ; one of crisis and despair. It is precisely at this point that Barth can and does affirm the place of ‘genuine’ philosophy. Kenneth Oakes develops this further for us as he writes:
One of the more suggestive returns of the correspondence model appears in Barth’s exegesis of Romans 8:28–39. In a section entitled ‘Love,’ Barth explains the suffering of creation, the sighs of creatures, and the work of philosophy in this way:
The man in this world knows only of the sighs of the creature and of his own sighs, (8:22–23), he can at least know (1:19–20) insofar as he does not evade the ‘emptiness’ of his existence (8:20), the dialectic of opposition, the relativity, and the homesickness of everything given, intuitable, and objective. Suffering sees to the salutary opening of our eyes, and, directly tied to the given boundaries of suffering, in its essence as the interpretation of this fact stands the philosophy worthy of its name. Thus in its not-knowing of God and his Kingdom, in its knowing the sighs of all created things, we agree with every truly profane, but not with any half-theological, consideration of nature and history. For precisely this not-knowing and this knowing are the blade and the flint from which, insofar as they together in spirit and truth, as the new and third thing, bursts forth the fire of the not-knowing knowing of God and of the knowing not-knowing of the emptiness of our existence, the fire of the love for God because he is God (5:5), while the theological, apparent knowledge of God and the apparent not-knowing of the emptiness of our existence neither meets in spirit and in truth, even less in fire, nor is able to ignite the fire of love for God.
Here Barth poetically describes a serious, critical philosophy, one that knows the suffering of creatures, and does not know the Kingdom of God. Philosophy is at its best, and most worthy of its title, when it is existentially involved in suffering and epistemologically sceptical regarding God. Philosophy is at its best when it is ‘serious’ and ‘profane.’ A philosophy of nature and history that is ‘half-theological’ is not as helpful to theology, nor as truthful about God and the world, as a philosophy that honestly considers human longing and suffering. It is this philosophy, and not an apparent theology or an apparent philosophy, which contains the blade (knowing suffering) and the flint (not knowing God) from which the fire of love for God might be ignited.
In addition to linking genuine philosophy to suffering, Barth also ties it to death. Barth calls death the ‘highest law’ in the world during his exegesis of the Adam and Christ contrast in Romans 5:12–21. All attempts at renewing and overcoming suffering and pains of the present world, including those found within ethics and philosophy, stand under the law of death:
morality can only appear as the denial of the body by the spirit, philosophy can only recognize itself in the form of the dying Scocrates, the spiritual life can only appear as the opposition to the affirmation of the natural life, progress can only happen in the restless negation of everything that is given and that exists, every flame (other than the flame of the Lord in Ex 3:2) can only burn as it consumes.
The practices and knowledges of ethics, philosophy, and religion all belong to the old world, to that which is passing away, even though they may still act as blade and flint and be transformed. Barth see this relationship between philosophy, truth, and death physically manifested in Nietzsche. While Nietzsche was ‘confronted by the truth,’ he finally perished before it.
The clearest example of the correspondence thesis can be found in the foreword to Romans II. Barth writes, alluding to Ecclesiastes 5:2,
‘God is in heaven and you are on the earth.’ The connection of this God to this man, the connection of this man to this God, is for me the theme of the Bible and the sum total (Summe) of philosophy in one. The philosophers call this crisis of human knowledge ‘the origin.’ The Bible sees Jesus Christ at this crossroads.
It would be difficult to find a more revealing passage as regards Barth and the correspondence thesis. McCormack argues, while Spieckermann implies as much, that ‘it was clearly the critical idealism of Heinrich Barth which was in view here. Karl was not offering a theoretical reflection on the relation of theology and philosophy.’ From the passages above it is clear that Barth does not have just any philosophy in mind when alludes positively to ‘philosophy,’ but critical, serious philosophy. The allusion to ‘the origin’ does suggest that Karl has Heinrich’s critical idealism and Ursprungsphilosophie in view. Nevertheless, Barth’s remark is also a more ‘theoretical’ and general reflection on the relation of theology and philosophy, for this passage still presumes there to be a correspondence between critical philosophy and modern Protestant theology. This ‘crisis philosophy’ can refer in particular to Heinrich’s Ursprungsphilosophie, and yet it is also clear that ‘serious’ philosophy, a ‘crisis philosophy,’ or a ‘philosophy worthy of its name’ would include other philosophers as well.
This is how Barth saw philosophy as a legitimate enterprise; it has correspondence with the human condition as that condition is narrated by the life of God in Jesus Christ. A condition that lives in crises and anxiety apart from its proper ground and orientation in Jesus Christ. Does this genuine philosophy, for Barth (according to Oakes’ accounting), have the capacity to enlighten people about God? Nein! Instead it has correspondence with what the cross of Jesus Christ and the God-man declare as it and He put death to death.
 Kenneth Oakes, Karl Barth on Theology&Philosophy (Oxford/New York: Oxford University Press, 2012), 82-4.