One's negation of God depends on the fact that God exists, has created and sustains all that is, including the predication of his supposed non-existence. This is the point of Van Til's illustration of the little girl that he saw, sitting on her father's lap, slapping him in the face. The slap itself could have its proper reference and meaning if and only if the father was holding up the little girl all the while. The little girl was "opposing" her father: in doing so. she was "presupposing" her father's support. even if she was unable or unwilling to affirm and articulate his support. Without that support, the slap was only a slap in the void. It had no referent, no meaning, no content.