Just after struggling so long with Spengler and having regretted including so many Germans in one year of my plan, I picked up Dietrich Bonhoeffer's Creation and Fall. I see great similarities in the styles of Kant, Hegel, Spengler, and Bonhoeffer. They're Germans, so they all want to be organized. But while their sometimes intricate tables of contents show a lot of organizational effort, their arguments often don't. Descartes thought of geometry as the most organized discipline, so he wrote some of his philosophical works like geometry books: he started with carefully explained axioms and built up his theorems bit by bit so the reader could (mostly) follow. But the Germans just jump into the middle of their ideas with special terminology and unexplained metaphors. Spengler, for instance, talks about the Baroque of the ancient world or about Faustian civilization as if they need no explanation. He doesn't explain until halfway through the book that the "West" of the title of his book doesn't mean what you probably think it means. Kant has his apodeictic judgments and his transcendental objects (which are different from transcendent objects), and Hegel has his reflections and negations. They often sound more like prophets than schoolteachers, receiving their mind-boggling visions from a greater Mind and then trying as hard as they can to describe the wheels within wheels.
Bonhoeffer fits right into this tradition of jumping into the middle of things. In fact, his first confusing metaphor is the very idea of the middle. Humans, he says, are in the middle. The Bible starts with a declaration of the beginning, which people in the middle can't understand and can't begin to know of without a revelation from God. Jesus is the Beginning and the End, and we are in the middle. It's pretty, and I think I learned something from the times Bonhoeffer used it. But is it a consistent metaphor? Does Jesus have a gap between beginning and end? Since we're in the middle, do we fill the gap in Jesus? (Pascal famously said the opposite.) Or are we in some other middle?
Bonhoeffer clearly gets this style from the Germans who preceded him, because he alludes to them frequently. Some of his allusions he makes explicit, some I recognized having read the other books, and some I discovered only by doing searches of some Latin phrases I didn't know. Bonhoeffer knows German philosophy and uses it often in this theological work, but he knows when to draw from it in a positive way and when to argue against it.
For instance, he says that the Day and Night created on (or themselves constituting) the first day represent the dialectic of creation, the constant ballet of existence and negation that all of creation dances. This dialectical idea is what Hegel is most famous for, and surely Bonhoeffer had Hegel in mind when he said this. Later he says that with the death of Christ on the cross "the nihil negativum broke its way into God's own being," another idea I just read in Hegel this past spring. But I notice that where Hegel says God's very essence involves the opposition of death and life, Bonhoeffer knows that God is Life alone and that death must "break its way" into God's being. In another place, he simply calls Hegel wrong for enthroning Reason in God's place. Bonhoeffer also explicitly contradicts Kant, who said that the only good thing possible is a good will, by pointing out that God declared his creation good.
I haven't read much Schopenhauer yet, but in looking up nihil negativum and its companion phrase nihil privativum, I found that they came from Schopenhauer's World as Will and Idea. (The latter is a nothingness that exists as an absence of something positive, as darkness is the absence of light. The former is absolute nothingness.) Bonhoeffer alludes to Nietzsche by saying that, before eating of the Tree of the Knowledge of Good and Evil, Adam lived beyond good and evil. He makes an interesting allusion to Freud's theory of dreams when he says that the common human dream of trying to escape something is a manifestation of the subconscious knowledge of our fallen state. And he refers to the popularizer of evolution simply by saying that the creation of Adam has nothing to do with Darwin.
Bonhoeffer's nuanced references to these philosophers encourages me. Obviously he had studied these non-Christian (or at the very least less-than-orthodox) philosophers, finding them not only not detrimental to the thinking of a Christian but even helpful. And now I'll cite an African, St. Augustine, who, in his treatise On Christian Doctrine, declared that "All truth is God's truth." All correct, wise, or beautiful statements are possible only because of God, so what does it matter what human utters them? Augustine's approval of the use of pagan literature in the education of Christians secured the place of the classics in the medieval curriculum; in fact, it probably saved a lot of literature we enjoy today from the ravages of both time and puritans. And now I benefit today from the works of pagan philosophers (Aristotle, Nietzsche, etc.), from the Christians who approved their study, and from Christians -- like Bonhoeffer -- who demonstrated the rewards of knowing them.