Abstract

William of Auvergne is one of the first Latin thinkers to discuss Avicenna’s cosmological theory of emanation and with it the famous principle «ex uno, secundum quod est unum, non est nisi unum». He accepts the validity of this principle itself, but vehemently rejects its use in the field of cosmology to explain God’s acting as the universe’s creator. Within the context of Trinitarian theology, however, William applies the ex-uno-principle to explain two core issues concerning the emanation of the second Trinitarian person out of the first: the theory of the only-begotten Son and the persons’ sharing of the one divine essence. In his treatment of the latter, William uses the Avicennian principle in a modified way which is illustrated in this paper.