One Person, Two Natures, Defined at Chalcedon

In 451 the Council of Chalcedon met to settle a dispute that had already split the church over how to describe Jesus Christ's divine and human natures. The council's definition, since known as the Chalcedonian formula, declared that Christ is fully God and fully man, one person known in two natures that exist without confusion, without change, without division and without separation. Each nature keeps its own properties intact; divinity is not diluted by humanity, and humanity is not swallowed up into divinity, yet the two are not two separate persons loosely joined but a single subject, the eternal Son, who possesses both natures completely. The formula was built to reject two opposite errors the council judged had already led churches astray. Nestorius had been read as dividing Christ into two persons, one divine and one human, joined only loosely, so that Mary could be called mother of the human Jesus but not mother of God. Eutyches, on the other side, was judged to have taught that Christ's humanity was absorbed into his divinity after the union, leaving only one composite nature. Chalcedon's four negative adverbs, without confusion, without change, without division, without separation, were chosen precisely to rule out both errors at once, holding that the union is real and complete while the distinction between the two natures is never erased.