Richard Cross

Aquinas distinguishes four types of part included in a hypostasis (’suppositum’): (1) kind-nature; (2) individuating feature(s); (3) accidents; (4) concrete parts. (1) - (3) in some sense contribute ’esse’ to the ’suppositum’. Usually Aquinas holds that Christ’s human nature does not contribute ’esse’ to its divine ’suppositum’, since it is analogous to a concrete part of its ’suppositum’. This effectively commits Aquinas to the Monophysite heresy. In ’De Unione’ Aquinas argues instead that Christ’s human nature contributes ’secondary ’esse‘ to its divine ’suppositum’. This account is coherent and orthodox, but sacrifices explanatory power.