The origins of the debate go back to the French theologian Henri de Lubac (1896-1991) and his book Surnaturel, which had a significant influence upon Vatican II.
In Surnaturel de Lubac argues that humans have a natural desire for God. That is to say, human nature possesses a natural, intrinsic, and created desire for a supernatural end. God implants in human nature a longing for union with God. As de Lubac argued, this belief was held by the early church fathers. You see it right there in Augustine's famous statement, "Our hearts are restless until they rest in Thee." Human life is restless and unfulfilled, less than what it was created to be, until it comes to rest in union with God.
Lubac's view won the day at Vatican II, and remains the widely held consensus. And I expect you agree. Of course humans were created for relationship with God! Who could disagree with this?
Well, one of authorities de Lubac cited in making his argument was Thomas Aquinas. And since the publication of Surnaturel Aquinas scholars have raised questions about if de Lubac read Aquinas correctly. In my assessment of the controversy, much of this has to do with Aquinas himself not being wholly consistent or clear, creating some interpretive ambiguity. Thus a fight emerged about the "correct" reading of Thomas.
The debate about a proper reading of Thomas need not concern us. But it might be asked, what is the opposing view to humans possessing a natural desire for God? The issue concerns what is called "pure nature."
The idea of "pure nature" suggests that human nature was created whole and complete in itself. Think of a tree. The nature of a tree is complete and whole in itself. A tree doesn't need anything "more" to be a flourishing tree. A tree just needs what all trees need: sun, soil, water. If those things are present, a tree will flourish. All due to the "logic" inherent in creation. No miracles or supernatural "extras" needed.
Now, what about a human being? The idea of pure nature says that humans are like trees. Humans have a nature and the "logic" of creation can actualize that nature to produce flourishing persons. Think of Maslow's hierarchy of needs. If you provide a human person with food, shelter, safety, esteem, care, and outlets for creativity and self-exploration human nature will "self-actualize." We'll grow like trees. None of this need involve God. Happiness isn't extrinsic to human nature, but intrinsic, built into our DNA so to speak. Human nature is whole and complete as it stands.
Let me come at the issue this way: Can an atheist be happy, well-adjusted, fulfilled, and self-actualized? If you say yes, or are tempted to say yes, then you're assenting to the idea of "pure nature." You're assenting to the view that human nature possesses a natural logic of happiness that is open and available to all human persons, simply because they are human persons. Just as the logic of gardening is available to all people, Christian and non-Christian alike, the logic of human flourishing, the science of happiness, is also available to all. An atheist, for example, can make an excellent therapist, possessing access to the science of flourishing, just as they can be an excellent gardener.
So, have you felt that big switcharoo in your head? At the start of the post we said, "Of course humans have a natural desire for God! Who would be crazy enough to deny it?" But now, after I've described the idea of "pure nature," some of you may be changing your answers: "Wait a minute. I do think atheists can be happy and well-adjusted. I know some." So which is it? Are those atheists secretly ailing, less fulfilled and actualized in their development because they lack God in their lives? Or are they truly happy without God, all on their own, because God has given human nature the gift of joy simply because we are a human person?
Suddenly, I hope you can see, the question about the relationship between nature and grace has become a lot more complicated.
