If anyone raises the objection that the terms essence and person are not sufficiently restrictive to express the mystery of the unity in the Trinity, then we may answer with Augustine: 'Human language labors under a truly great paucity of words. We speak of three persons not in order to say just that, but rather so as not to be silent altogether (De Trin. V)'
-- F. Pieper, "Doctrine of God" from Christian Dogmatics, Vol. I