a Greek term, literally signifying substance, or subsistence, and used in theology for person. The word is Greek, ἰστάσις, compounded of ὑπό, sub, under, and εἰστι, sto, existo, I stand, I exist; as if we were to say subsistentia. Thus we hold that there is but one nature or essence in God, but three hypostases or persons. The term hypostasis is of a very ancient standing in the church. St Cyril repeats it several times, as also the phrase "union according to hypostasis." The first time it occurs is in a letter from that father to Nestorius, where he uses it instead of ἰστάσις, the word we commonly render person, which did not seem expressive enough. "The philosophers," says St Cyril, "have allowed three hypostases. They have extended the divinity to three hypostases; they have even sometimes used the word trinity; and nothing was wanting but to have admitted the consubstantiality of the three hypostases, to show the unity of the divine nature, exclusively of all triplicity in respect of distinction of nature, and not to hold it necessary to conceive any respective inferiority of hypostases."

This term occasioned great dissensions in the ancient church; first amongst the Greeks, and afterwards amongst the Latins. In the council of Nice, hypostasis was defined to denote the same thing with essence or substance; so that it was heresy to say that Jesus Christ was of a different hypostasis from the Father; but custom altered the meaning of the term. In the necessity they were under of expressing themselves strongly against the Sabellians, the Greeks made choice of the word hypostasis, and the Latins of the word persona; a change which proved the occasion of endless disagreement. The phrase ἰστάσις, ἰστάσις, used by the Greeks, scandalized the Latins, whose usual way of rendering ἰστάσις in their language was by substantia. The barrenness of the Latin tongue in theological phrases allowed them but one word for the two Greek ones, ἰστάσις and ἰστάσις, and thus disabled them from distinguishing essence and hypostasis; for which reason they chose rather to use the term tres personas, and tres hypostases. But an end was put to disputation, in a synod held at Alexandria about the year 362, at which St Athanasius assisted; and from this time the Latins made no great scruple of saying tres hypostases, nor the Greeks of saying tres personas.