Contrary to Barlaam, Gregory asserted that the prophets in fact had greater knowledge of God, because they had actually seen or heard God himself. Addressing the question of how it is possible for humans to have knowledge of a transcendent and unknowable God, he drew a distinction between knowing God in his '''essence''' (in Greek, ουσιαουσία) and knowing God in his '''energies''' (in Greek, ενεργειαιενέργειαι). He maintained the Orthodox doctrine that it remains impossible to know God in his essence (God in himself), but possible to know God in his energies (to know what God does, and who he is in relation to the creation and to man), as God reveals himself to humanity. In doing so, he made reference to the [[Cappadocian Fathers]] and other early Christian writers.