Enough beating up on Rahner for the moment. He has this statement in Nature and Grace : “there has been no ‘chemically pure’ description of pure nature, but mixed in with it there are traces of elements of historical nature, i.e., nature possessing grace. Who is to say that the voice heard in earthly philosophy, even non-Christian and pre-Christian philosophy, is the voice of nature alone (and perhaps of nature’s guilt) and not also the groaning of the creature, who is already moved in secret by the Holy Spirit of grace, and longs without realizing it for the glory of the children of God?”

Rahner’s answer is that we cannot tell; there is in fact nothing that is identifiable as the voice of “nature alone.” If he’d take the last step and say that nature’s voice is impossible to hear because nature doesn’t exist alone, even conceptually, I’d rest happy.