a Greek term, literally signifying substance, or subsistence; used in theology for person. The word is Greek, ὑποστάσις; compounded of ὑπό sub, "under," and στάσις, ἀπό, exstis, "I stand, I exist;" q. d. subsistence. 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 προσώπων, 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, exclusive of all triunity 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 among the Greeks, and afterwards also among the Latins. In the council of Nice, hypostasis was defined to denote the same with essence or substance; so that it was hereby to say that Jesus Christ was of a different hypostasis from the Father; but custom altered its meaning. 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 persona; which change proved the occasion of endless disagreement. The phrase τρεῖς ὑποστάσεις, used by the Greeks, scandalized the Latins, whose usual way of rendering ὑποστάσις in their language was by substantia. The baronets of the Latin tongue in theological phrases, allowed them but one word for the two Greek ones, ὑπόστασις and ὑποστάσις; and thus disabled them from distinguishing essence from hypostasis. For which reason they chose rather to use the term tres personas, and tres hypostases.—An end was put to logomachies, in a synod held at Alexandria about the year 362, at which St Athanasius assisted; from which time the Latins made no great scruple of saying tres hypostases, nor the Greeks of three persons.