Ousia and Hypostasis in the Nicene Creed

Summary

The Nicene Creed of AD 325 seems to use the terms hypostasis (Person) and ousia (substance) as synonyms when it anathematizes those who say that the “Son of God” is of a different hypostasis or ousia than the “one God Father Almighty.” That would also mean that the Son is the same hypostasis (Person) as the Father, which would contradict the Trinity doctrine, in which the Father and Son are two distinct Persons but one substance or Being. In fact, that anathema seems to teach Sabellianism in which the Father, Son, and Holy Spirit are one single hypostasis (Person).

To explain these terms, this article shows that, during the centuries before Nicaea and during most of the Arian Controversy, hypostasis and ousia were indeed used as synonyms. Although there was, during that period, significant confusion about the meaning of these terms, ousia did not mean “substance.” Rather, both hypostasis and ousia were used for “Person.”

It was mainly under the influence of the Cappadocian Fathers, in particular Basil of Caesarea, after the year 360, that the terminology was standardized so that the formula ‘three hypostases in one ousia’ came to be accepted as an epitome of the orthodox doctrine of the Trinity.

The Cappadocians proposed these more specific meanings because, in contrast to the Sabellians, they recognized three distinct Realities (Father, Son, and Holy Spirit) but regarded them as equal in every respect. However, then the anti-Nicenes would object that that implies three First Principles (three Beings who exist without cause and who gave existence to all else). So, they proposed the distinction to say the Father, Son, and Holy Spirit are three Realities (Persons) but only one First Principle (ousia).

In other words, Basil did not simply propose specific meanings for the two terms. His purpose was to formulate a distinction between the three distinct Realities (Persons) and the one First Principle and assigned meanings to the terms to assist with that distinction.

But when the Nicene Creed was formulated, this distinction did not yet clearly exist. Hypostasis and ousia did not yet mean “Person” and “substance” respectively. When the Creed was formulated, the two terms still had pretty must the same meaning and both meant ‘person'. Therefore:

Firstly, the Nicene Creed does indeed use the two terms as synonyms and that anathema does indeed imply Sabellianism.

Secondly, since that distinction is the epitome of the Trinity doctrine, the Trinity doctrine did not yet exist when the Nicene Creed was formulated.

Purpose

The Anathema

The Nicene Creed of AD 325 anathematizes those who say that the “Son of God,” compared to the “one God Father Almighty,”

“Is of a different hypostasis (ὑποστάσεως) or substance (οὐσιάς, transliterated as ousia).” (Early Church Texts)

The terms “ousia and hypostasis” are “one of the most striking aspects of Nicaea.” These terms have not appeared in any previous creed and also do not appear in the creed formulated just a few months earlier at Antioch. (LA, 92) Hanson describes them as “new terms” (RH, 846).

The anathema seems to use the terms hypostasis and ousia as synonyms:

Ayres refers to “the seeming equation of ousia and hypostasis (LA, 88).

R.P.C. Hanson says that “N (the Nicene Creed) ... apparently (but not quite certainly) identifies hypostasis and ousia” (RH, 187).

Consequently, the anathema seems to say that the Son of God is the same hypostasis (Person) as the “one God Father Almighty." This would be a contradiction of the Trinity doctrine in which the Father and the Son are:

• Two different hypostases (Persons)
• In one ousia (Being or substance).

In fact, by describing the Father and the Son as the same hypostasis AND as the same ousía, that anathema seems to teach Sabellianism in which the Father, Son, and Holy Spirit are three parts of one single ‘Person’. R.P.C. Hanson says of the condemnation quoted above:

“By the standard of later orthodoxy, as achieved in the Creed of Constantinople of 381, it is a rankly heretical (i.e. Sabellian) proposition, because the Son must be of a different hypostasis (i.e. 'Person') from the Father. And in fact there were present at the Council people, such as Marcellus of Ancyra, who were quite ready to maintain that there is only one hypostasis in the Godhead, and who were later to be deposed for heresy because they believed this.” (RH, 167) (“Marcellus of Ancyra had produced a theology … which could quite properly be called Sabellian” (RH, ix))

“The Creed of Nicaea of 325 … ultimately confounded the confusion because its use of the words ousia and hypostasis was so ambiguous as to suggest that the Fathers of Nicaea had fallen into Sabellianism, a view recognized as a heresy even at that period.” (Hanson)

The Holy Spirit

This anathema does not mention the Holy Spirit, just as the Creed does not say that the Holy Spirit is “God” or “of one substance with the Father.” The Nicene Creed, in its 325-form, focused on the Son. For that reason, this article also focuses only on the Father and Son.

Purpose

The purpose of this article is to determine whether that is really what the Creed says. For that purpose, it explains how these terms were used in the time leading up to the Nicene and in the rest of the fourth century. From this analysis, we can conclude whether the Nicene Creed teaches or contradicts the Trinity doctrine.

Authors

This article uses the following codes for referring to the books of three world-class scholars who are regarded as specialists in the fourth-century Arian Controversy:

RH = Bishop RPC Hanson The Search for the Christian Doctrine of God - The Arian Controversy 318-381, 1987

RW = Archbishop Rowan Williams Arius: Heresy and Tradition, 2002/1987

LA = Lewis Ayres Nicaea and its legacy, 2004 Ayres is a Professor of Catholic and Historical Theology

As far as possible, I quote from these scholars but I also want to explain these complex principles as simple as possible. For that reason, I sometimes abbreviate or paraphrase what they wrote.

Centuries before Nicaea

This section discusses how these terms were used in the centuries before Nicaea.

Etymology

Etymologically (i.e., relating to the origin and historical development of words and their meanings), hypostasis and ousia are direct cognates (See - Ousía and hypostasis from the philosophers to the councils). That means that these two words have the same linguistic derivation, just like the English father, the German Vater and the Latin pater are cognates. In other words, originally, therefore, hypostasis and ousia had the same meaning.

In Greek Philosophy

“Hypostasis … became a key-word in Platonism.” (RH, 182) Hanson says hypostasis and ousia were “borrowed from the pagan philosophy of the day” (RH, 846).

Ancient Greek philosophers also used these terms as synonyms. They used both ousía and hypostasis as meaning:

• "That which stands under;" and
• "The fundamental reality that supports all else."
• The primary, fundamental kind of being, in contrast to the objects in the sensible world which are mere shadows.

In other words, they used these terms to describe God.

In the Bible

The Bible does not use these terms to describe God. Hanson says:

“The pro-Nicenes are at their worst, their most grotesque, when they try to show that the new terms borrowed from the pagan philosophy of the day were really to be found in Scripture.” (RH, 846)

Ousia

The Bible never uses ousia to describe God. For a definition, see - The Free Dictionary or Liddell & Scott.

Hypostasis

“The word occurs five times in the New Testament” (RH, 182):

In the four instances where it is used NOT with reference to God, it is translated as 'confidence' and ‘assurance’ (2 Cor 9:4; 11:17; Heb 3:14; 11:1); consistent with the concept of 'fundamental reality' in Greek philosophy.

The fifth instance is Hebrews 1:3, in which “the Son is described as the impression (character) of the Father's hypostasis and this must mean his nature.” (RH, 187) “It denotes God's being or nature.” (RH, 182)

The word hypostasis also appears once in the Greek translation of the Old Testament:

“In the LXX, … at Wisdom 16:21 the writer speaks of God's hypostasis, meaning his nature.” (RH, 182)

Note that, while hypostasis, today, is commonly understood to mean “Person,” in these two verses it is mostly translated as the "nature" of God (BibleHub).

In Origen's writings

Origen wrote at the beginning of the third century. He was the most influential writer of the first three centuries. "The great majority of the Eastern clergy were ultimately disciples of Origen." (Bible.ca, quoting W.H.C. Frend):

“For Origen the words hypostasis … and ousia are … synonyms for the same thing - distinct individual entity." (RH, 66-67)

He “used hypostasis and ousia freely as interchangeable terms to describe the Son's distinct reality within the Godhead." (RH, 185)

As an example where Origen used these as interchangeable terms (synonyms), he "can argue … that the Logos is … separate in hypostasis or ousia from the Father." (RH, 66-67)

As an example where Origen used these terms for a "distinct reality" (a Person, we might say), "he taught that there were three hypostases within the Godhead.” (RH, 184)

However, while Origen wrote that the Son is "separate in hypostasis or ousia from the Father" (RH, 66-67), the Nicene Creed states the opposite and condemns those who say that He “is of a different hypostasis or substance.

So, while ousia is understood today as "substance," Origen used it for "Person" (a distinct reality):

"He can say … that the Son is 'different in ousia' from the Father, meaning that he is a distinct entity from the Father." (RH, 66-67)

"His statement … that the Son 'does not differ' in ousia from the Father does not … mean that the ousiai of the Father and Son are identical; the subsequent passage makes it perfectly clear … that they are distinct. But Origen means that they are not unlike, not of different natures.” (RH, 66-67)

Dionysius of Rome

Bishop Dionysius of Rome (in the middle of the third century) also used hypostases for ‘distinct individual entity’. For example, he “said that it is wrong to divide the divine monarchy 'into three sorts of … separated hypostases and three Godheads'; people who hold this in effect produce three gods.” (RH, 185)

Conclusion

So, in summary:

• In terms of origin, hypostasis and ousia are cognates (the same or similar nature), just like the English father and the German Vater.
• Greek Philosophy used them as synonyms for "the fundamental reality that supports all else” (“God” in modern English).
• The New Testament uses hypostasis once for God’s “nature” but never refers to God’s ousia.
• Origen, a century before Nicaea, used the terms as synonyms for a “distinct individual entity" (a divine Person).
• Bishop Dionysius of Rome, about 60 years before Nicaea, also used hypostases for ‘distinct individual entity’.

Therefore, in the time before the Arian Controversy:

• The two terms were used as synonyms,
• For "a distinct individual entity."

In other words, ousia was NOT used for the substance of God. Williams refers to “the respectable pre-Nicene usage of ousia for primary (individual) substance." (RW, 164)

When the Controversy began

Confusion

“Considerable confusion existed about the use of the terms hypostasis and ousia at the period when the Arian Controversy broke out.” (RH, 181) “Several alternative ways of treating these terms were prevalent.” (RH, 184)

Synonyms

“For many people at the beginning of the fourth century the word hypostasis and the word ousia had pretty well the same meaning:” (RH, 181)

“It is … likely that when Narcissus of Neronias at the Council of Antioch in 325 declared to Ossius that he believed in three ousiai he was equating ousia with hypostasis.” (RH, 187)

“Eusebius of Caesarea appears to accept the equation of hypostasis and ousia in the anathema of N quite readily.” (RH, 185)

But with different meanings

However, different authors gave different meanings to the same word. For example:

Ousia

Eusebius of Nicomedia used ousia to describe the Persons (distinct individual entities) of the Godhead. For example, he said “there are two ousiai and two facts (or "things")” (RH, 185-6)

“Eusebius of Caesarea … uses ousia to mean substance.” (RH, 185)

Hypostasis

“Alexander of Alexandria … does not use the word ousia, but instead uses hypostasis for both 'Person' and 'substance'” (RH, 186)

The manifesto of Antioch in 325, shortly before the Nicene Council “uses hypostasis to mean 'substance' or 'nature'” (RH, 188).

Some used the terms in the “orthodox way.”

“When at last the confusion was cleared up and these two distinct meanings were permanently attached to these words,” hypostasis and ousia meant “'person' and 'substance'.” (RH, 181) But it seems as if some ‘Arians’ already used these terms in that way. Arius, for example:

Said that the hypostases of Father, Son and Holy Spirit “were different in kind and in rank.” (RH, 187) (In other words, he used hypostasis for a "distinct individual reality’.)

Wrote, “The Father is alien in ousia to the Son” (RH, 186) and “the Logos is alien and unlike in all respects to the Father's ousia.” (RH, 186) (In these instances, he used ousia for "substance.“)

Hanson concludes:

“It seems likely that he was one of the few during this period who did not confuse the two.” (RH, 187)

Another leading “Arian” “who clearly did not confuse ousia and hypostasis” was Asterius. (RH, 187):

He “said that there were three hypostases” and “certainly taught that the Father and the Son were distinct and different in their hypostases.” (RH, 187)

“He also described the Son as 'the exact image of the ousia and counsel and glory and power' of the Father.”

Note also, from these quotes, that Arius thought that “the Father is alien in ousia to the Son,” meaning that the Son's substance is very different from the Father's. In contrast, Asterius said that the Son is "the exact image of the ousia' of the Father.” “He thought that the resemblance of the Son to the Father was closer than Arius conceived.” (RH, 187) As discussed, the so-called 'Arians' were not followers of Arius.

Conclusion

“The state of affairs as regards the use of hypostasis and ousia at the outset of … the Arian Controversy can ... be stated (as) … a general state of indecision and uncertainty as to how either of them should be used:” (RH, 184-185)

Decades after Nicaea

“For at least the first half of the period 318-381, and in some cases considerably later, ousia and hypostasis are used as virtual synonyms.” (RH, 183) “It is only much later in the century that the two are more clearly distinguished by some.” (LA, 98)

“The distinction in meaning between ousia and hypostasis (both of which mean ‘something that subsists’) was worked out only in the late fourth century.” (Lienhard, Joseph T. Ousia and Hypostasis: The Cappadocian Settlement and the Theology of ‘One Hypostasis’. Oxford University Press.)

The Cappadocians

“It was mainly under the influence of the Cappadocian Fathers that the terminology was clarified and standardized so that the formula ‘three hypostases in one ousia’ came to be accepted as an epitome of the orthodox doctrine of the Trinity.” (González, Justo L. (1987). A History of Christian Thought)

Hanson similarly says that, even though some (in the time before the Cappadocians) “distinguished hypostasis, meaning distinct reality, from ousia, meaning 'nature' or even 'substance',” this does not mean that they have “anticipated the later meanings of those terms given to them in the second half of the century by the great Cappadoclan theologians.” He gives examples. For example:

“The concept of what we would now call the 'Persons' of the Trinity … had barely dawned on the consciousness of theologians.” (RH, 190)

“The concept of what each Person of the Trinity is in his existence and proper form distinct from the others had not yet been distinguished from the concept of what all of them were as full and equal (or even as partial and unequal) sharers of the Godhead.” (RH, 190)

Basil of Caesarea

Basil of Caesarea, one of the three Cappadocians, is in particular credited with this development:

“In some accounts Basil is the architect of the pro-Nicene triumph:” He “develops an account of the distinctions between persons and essence of such power that the final victory of pro-Nicene theology under the Emperor Theodosius is inevitable.” (LA, 187)

“The first person to propose a difference in the meanings of hypostasis and ousía, and for using hypostasis as synonym of Person, was Basil of Caesarea” (Johannes, "Ousía and hypostasis from the philosophers to the councils"), namely in his letter 214 (AD 375) and Letter 236 (AD 376).

Michael Pomazansky, in discussing the fact that the Nicene Creed uses the terms hypostasis (person) and ousia (substance) as synonyms, remarks: “Finally, following the authoritative example of St. Basil the Great, it became accepted to understand by the word Hypostasis the Personal attributes in the Triune Divinity.” (Orthodox Dogmatic Theology, p. 94-95). (Britannica)

Since Basil was born only born after the Creed was formulated (“around 330” (LA, 187)), the distinction between hypostasis and ousia did not yet exist when the Nicene Creed was formulated. In the Council itself, the two terms still had a similar meaning.

It is not just that the meanings of the terms changed; Basil formulated these meanings for these terms to establish the distinction between Being and Person:

Basil “is often identified” with the “distinction between a unitary shared nature at one level, and the personal distinctions of Father, Son, and Spirit at another.” (LA, 190-191)

This is important because it means that the concept of three Persons in one Being is not to be found in the Nicene Creed.

Why the meanings changed

On pages 189-190, Ayres discusses Basil's motivation for developing the concept that God is one Being but three Persons. In brief:

Firstly, the Sabellians interpreted h*m*ousios as meaning that the Father, Son, and Holy Spirit are one single Reality (Person). Basil did not agree. He wanted to say that they are distinct but the same in every way.

However, then the anti-Nicenes objected that this implies three Ultimate Principles (three Beings who exist without cause and who are the cause of all life).

So, Basil developed the distinction to enable him to say they are three Realities (Persons) but only one Ultimate Principle (ousia).

To quote Ayres more fully:

In Letter 361, Basil seems to have had two concerns “about the difficulty of understanding h*m*ousios appropriately:” (LA, 189)

“On the one hand, Basil may be expressing an anti-Marcellan concern with h*m*ousios.” (LA, 190) Basil understood the phrase “light from light” to “speak clearly of two realities.” His concern was that h*m*ousios may imply “that Father and Son are the same one light;” (LA, 190) (one single reality), as claimed by the Sabellians and Marcellus.

“On the other hand … it may well be that Basil of Caesarea's concern in Letter 361 is” “that h*m*ousios implies Father and Son are of identical ontological status. (In that case) Homoousios is unacceptable because it implies the existence of two ultimate principles.” (LA, 190) “To speak of Father and Son as simply having the same ousia would be … to present him as logically another God.” (LA, 190)

“Basil's new distinctions have provided him with an understanding of h*m*ousios that overcomes his earlier concerns.” (LA, 195)

Developed through Epinoia.

In brief, the anti-Nicenes said that the Bible teaches that only the Father exists without cause. Therefore, no other being can be equal to Him. But Basil argued that, if we reflect (epinoia) on certain texts, then "there is a unity of ousia between Father and Son." To quote Ayres more fully:

“Basil's Contra Eunomium,” consisting of “three books,” “probably finished in 363 or 364” (LA, 191) opposed the teachings of Eunomius, the leading ‘Neo-Arian’, also known as a hetero-ousian, meaning that he taught that the Son’s substance is different from the Father’s.

As Ayres discusses on pages 191 and following, Basil and Eunomius had different approaches:

For Eunomius, the main distinction between God and all other beings, including His Son, is that God is “ingenerate” (exists without cause). (LA, 194) “Ingenerate,” therefore, is “the primary name of God.”

Basil responded that “ingenerateness” is merely the absence of a quality “and hence it is unsuitable as the primary name of God.” (LA, 194) He argued that if ingenerateness is God’s primary identification, then “Father and Son are unlike” (LA, 194) and this, he argues, “flies in the face of biblical material such as Col 1:15, Heb 1:3, and Phil 2:6.”

Basil explained, on the basis of such texts, “by epinoia we know that there is a unity of ousia between Father and Son.” (LA, 194) Epinoia means “concepts developed by the human mind,” through “a process of reflection and abstraction” (LA, 191-2). Epinoia, therefore, means to extrapolate the text of the Bible beyond what it literally says. But Eunomius objected saying, “If we know God only according to epinoia, then our knowledge is insignificant and our faith useless.” (LA, 195)

The Distinction

Basil explained:

“The distinction between ousia and hypostases is the same as that between the general and the particular; as, for instance, between the animal and the particular man. Wherefore, in the case of the Godhead, we confess one essence or substance so as not to give variant definition of existence, but we confess a particular hypostasis, in order that our conception of Father, Son, and Holy Spirit may be without confusion and clear.” (González, Justo L. (1987). A History of Christian Thought: From the Beginnings to the Council of Chalcedon. Nashville, TN: Abingdon Press. p. 307.)

Gregory of Nyssa (AD 380)

After Basil of Caesarea, in c. 380, Gregory of Nyssa, another of the Cappadocians, devotes his letter 35 to the difference between ousía and hypostasis.

Council of Chalcedon

However, after the Cappadocians, many Latin-speaking theologians continued to use hypostasis and substance as synonyms. It was only from the middle of the fifth century onwards, marked by the Council of Chalcedon, that the word came to be contrasted with ousia and used to mean "individual reality," especially in the trinitarian and Christological contexts. (González, Justo L. (1987). A History of Christian Thought: From the Beginnings to the Council of Chalcedon. Nashville, TN: Abingdon Press. p. 307.)

Conclusions

Confusion

So, when the Controversy began, and for a considerable time afterward, there was “a general state of indecision and uncertainty as to how either of them should be used.” (RH, 184-185) “The ambiguous anathema in N against those who believe that the Son is 'from another hypostasis or ousia than the Father” was the consequence of “this unfortunate semantic misunderstanding.” (RH, 181)

This confusion helps to explain why the Controversy continued for another 55 years after Nicaea:

“When apparent agreement was reached at Nicaea in 325 the Creed … contained in one of its anathemas a confusion of terms so disastrous as to render its eirenic function (to promote peace or reconciliation) virtually worthless” (RH, xviii)

Synonyms

Since “for many people at the beginning of the fourth century the word hypostasis and the word ousia had pretty well the same meaning” (RH, 181), and since the Creed itself seems to use these terms as synonyms, it is quite possible that the Creed does indeed use “ousia and hypostasis” as synonyms. “It is only much later in the century that the two are more clearly distinguished by some.” (LA, 98)

Therefore, referring to the terms hypostasis and ousia in the Nicene Creed, R.P.C. Hanson states:

“They did not mean, and should not be translated, 'person' and 'substance', as they were used when at last the confusion was cleared up and these two distinct meanings were permanently attached to these words.” (RH, 181)

No Trinity Doctrine

One important implication is that the Trinity doctrine did not exist when the Nicene Creed was formulated in AD 325 because:

• The distinction between hypostases (Persons) and ousia (Being or substance) is foundational in the Trinity doctrine, and because
• That distinction was only developed decades later.

It is important to understand that 'Pro-Nicene theology' is different from 'Nicene theology'. Lewis Ayres wrote:

“By ‘pro-Nicene’ I mean those theologies, appearing from the 360s to the 380s … of how the Nicene creed should be understood. … These theologies build closely on and adapt themes found earlier in the century, but none is identical with any original ‘Nicene’ theology apparent in the 320s or 330s.” (LA, 6)

Sabellian

Furthermore, since the Creed uses hypostasis and ousia as synonyms, it indeed says that the Son of God is the same hypostasis (Person) as the Father, which is a clear Sabellian statement.

The Wikipedia article on Hypostasis makes it clear that there was some confusion in terminology due to language difficulties of Latin, Greek and English.

The concepts being referred to are confused by misunderstanding what 'substance' and 'essence' actually mean when applied to Divine Persons.

It was mainly under the influence of the Cappadocian Fathers that the terminology was clarified and standardized so that the formula "three hypostases in one ousia" came to be accepted as an epitome of the orthodox doctrine of the Trinity.[5] Specifically, Basil of Caesarea argues that the two terms are not synonymous and that they, therefore, are not to be used indiscriminately in referring to the godhead. He writes:

The distinction between ousia and hypostases is the same as that between the general and the particular; as, for instance, between the animal and the particular man. Wherefore, in the case of the Godhead, we confess one essence or substance so as not to give variant definition of existence, but we confess a particular hypostasis, in order that our conception of Father, Son, and Holy Spirit may be without confusion and clear.[5]

This consensus, however, was not achieved without some confusion at first in the minds of Western theologians since in the West the vocabulary was different. Many Latin-speaking theologians understood hypo-stasis as "sub-stantia" (substance); thus when speaking of three "hypostases" in the godhead, they might suspect three "substances" or tritheism. However, from the middle of the fifth century onwards, marked by Council of Chalcedon, the word came to be contrasted with ousia and used to mean "individual reality," especially in the trinitarian and Christological contexts. The Christian concept of the Trinity is often described as being one god existing in three distinct hypostases/personae/persons.[6]

Purpose

The original Nicene Creed, formulated in the year 325 AD, in the condemnations at the end of it, denounces:

“Those who say … that the Son of God is of a different hypostasis (ὑποστάσεως) or substance (οὐσιάς)” (Early Church Texts).

"Substance" (οὐσιάς) is transliterated as ousia. In other words, according to the creed, the words hypostasis and ousia are synonyms and the Son of God is both of the same hypostasis as the Father and of the same ousia or substance as the Father. This causes the following anomalies:

(1) While, in the Creed, the Son is of the same hypostasis as the Father, in the Trinity doctrine, the Father and the Son are different hypostases (Persons).

(2) While the Creed uses hypostasis and ousia as synonyms, in the Trinity doctrine, hypostasis and ousia differ in meaning: The Father, Son, and Holy Spirit are three hypostases (Persons) but in one ousia (substance or being).

(3) By describing the Father and the Son as the same hypostasis and as the same ousía, the creed seems to teach Sabellianism (modalism), in which the Father, Son, and Holy Spirit are one Person (one mind and one will) wearing three faces or masks, like a single person playing three characters in a theatre. However, Sabellianism has already been rejected before the Nicene Creed was formulated.

To address these anomalies, this article discusses the original meanings of these words and how the meanings changed over time.

Original Meaning of Hypostasis

Etymology

Etymologically (i.e., relating to the origin and historical development of words and their meanings), ὑποστάσεως (hypostasis) is a direct cognate of οὐσιάς (substance) (See, Ousía and hypostasis from the philosophers to the councils). This means that these two words have the same linguistic derivation. Examples of other cognates are the English father, German Vater, and Latin pater. Originally, therefore, ὑποστάσεως (hypostasis) and οὐσιάς (substance) had the same meaning.

In Greek Philosophy

Both ousía and hypostasis, originally, meant "that which stands under." The ancient Greek philosophers used these terms to describe real entities as having substance - "the fundamental reality that supports all else," in contrast to imaginary entities:

“Hypostasis is the underlying state or underlying substance and is the fundamental reality that supports all else” (Hypostasis - Wikipedia)

In Hebrews 1:3

Hypostasis appears only once in the Bible, namely in Hebrews 1:3:

“His Son … is the exact representation of His (God’s) υποστασις (hypostasis).”

Although hypostasis, today, is commonly interpreted to mean “Person,” in this verse, it is translated as "substance" (ASV) or as “nature” (NASB). In this verse, therefore, hypostasis has the same meaning as it had for the ancient Greeks. Similarly, Strong's Greek: 5287 - ὑπόστασις (hupostasis) explains it as meaning “a support, substance, steadiness, hence assurance.”

How did the meaning change?

Since hypostasis originally meant "substance, nature, or essence," how and why did its meaning change to "person?"

The meaning of hypostasis did not change over time as a natural process of evolution in how the word was used. Rather, the meaning was changed as a result of an explicit proposal by one theologian that became generally accepted in the church as a means to interpret the Nicene Creed as to not teach Sabellianism. To explain this, we need to trace the history of this word:

First Three Centuries

In the first three centuries, Origen and other Christian writers used hypostasis in the same way as the Greek philosophers did before them, namely to denote "being" or "substantive reality." They used hypostasis as a synonym for ousia (substance). (Ramelli, Ilaria (2012). "Origen, Greek Philosophy, and the Birth of the Trinitarian Meaning of Hypostasis". The Harvard Theological Review. 105 (3): 302–350.doi:10.1017/S0017816012000120.JSTOR 23327679, p. 302-350.)

For a definition of ousia, see, for example, Homoousion - definition of Homoousion by The Free Dictionary or [οὐσία][8] in Liddell & Scott.

Nicene Creed - 325

As discussed above, this is also how hypostasis was used in the anathemas appended to the Nicene Creed.

Five decades after Nicaea

The meaning of hypostasis was changed during the five decades after Nicaea. The council added the word h*m*-ousios (same substance) on the insistence of Emperor Constantine (Jörg Ulrich. "Nicaea and the West." Vigiliae Christianae 51, no. 1 (1997), p15) [God in Three Persons, Millard J. Erickson][9], p82-85.

As indicated by the large number of creeds which the church fathers formulated in the 50 years after Nicaea (see [Arian creeds - Wikipedia][10]), particularly to find alternatives for the word h*m*-ousios (see [Fourth Century Arianism][11] or [Arianism - Wikipedia][12]), the church reacted quite strongly against the word h*m*-ousios:

At the time, one main argument against the word h*m*-ousios was, with respect to words such as "Latin substantia, but in Greek ousia," "that in divine Scripture nothing is written about them and that they are above men’s knowledge and above men’s understanding" ([Fourth Century Christianity - Second Creed of Sirmium - 358][13]). This is called Homo-ianism (see [Acacians - Wikipedia][14]). RPC Hanson lists twelve creeds from the fourth century that reflect the Homoian faith (Hanson R. P. C. 2005, The Search for the Christian Doctrine of God: The Arian Controversy 318-381 AD. A&C Black. ISBN 978-0-567-03092-4, pp. 558–559)

But another great objection, as explained above, was that the description of the Son as of the same hypostasis and of the same ousia as the Father teaches modalism. It was explicitly to counter the suspicion that the creed teaches modalism that supporters of the Nicene Creed proposed a new meaning for hypostasis:

Basil of Caesarea (AD 375)

The first person to propose a difference in the meanings of hypostasis and ousía, and for using hypostasis as a synonym of person, was Basil of Caesarea, namely in his letters 214 (AD 375 - [Letter 214][15]) and 236 (AD 376 - [Letter 236][16]) (See also Ousía and hypostasis from the philosophers to the councils or Turcescu, Lucian (1997). "Prosopon and Hypostasis in Basil of Caesarea's "Against Eunomius" and the Epistles". Vigiliae Christianae. 51 (4), JSTOR 1583868, p. 374-395.) In both letters, his main motive was to neutralize the objection of the opponents of the Nicene Creed that, to speak of the Father and the Son as one hypostasis, is Sabellianism (modalism).

Gregory of Nyssa (AD 380)

After Basil of Caesarea, in c. 380, Gregory of Nyssa devotes his letter 35 to the difference between ousía and hypostasis (Letter-35).

Emperor Theodosius (AD 380)

As stated, during the five decades after Nicaea, the church opposed the Nicene Creed and formulated various alternative creeds, each proposing alternatives for the word h*m*-ousios in the Nicene Creed (See [Arian creeds - Wikipedia][10]). In 380, Emperor Theodosius made an abrupt end to this period.

Before Theodosius became emperor, as indicated by the contents of the creeds of that period (See, Arian creeds - Wikipedia), the Nicene supporters were in the minority. When he became emperor, "Arianism was widespread in the eastern half of the Empire" (Williams, Stephen; Friell, Gerard (1994). Theodosius: The Empire at Bay. B.T. Batsford Ltd. ISBN 0-300-06173-0, pp. 46–53).

In February 380, the 23-year-old emperor, through the [Edict of Thessalonica][17], declared:

"Let us believe in the one deity of the Father, the Son, and the Holy Spirit, in equal majesty and in a holy Trinity."

"This edict was the first known secular Roman law to positively define a religious orthodoxy" (Errington, R. Malcolm (2006). Roman Imperial Policy from Julian to Theodosius. Chapel Hill: University of North Carolina Press. ISBN 0-8078-3038-0, p. 217.)

Enforcement

The Edict of Thessalonica authorized imperial punishment for those who oppose it.

On 26 November 380, two days after he had arrived in Constantinople, Theodosius expelled the Homo-ian bishop (See [Theodosius I - Wikipedia][18]). (The Homo-ians are the people who refused to get involved in the debate about the substance of God because His substance is not revealed in the Bible. See [Acacians - Wikipedia][14].)

Through persecution, Theodosius destroyed all resistance to his theology:

"In January of the following year (381), another edict forbade the heretics to settle in the cities." ([Boyd, The Ecclesiastical Edicts of the Theodosian Code, page 45][19]) (cf. Richard Rubenstein, When Jesus Became God, 1999, p. 223).

"In the same year, after the reformulation of the Nicene doctrine by the Council of Constantinople ... the procouncil of Asia was ordered to deliver all churches to these bishops 'who profess that the Father, Son and Holy Spirit are one majesty and virtue'" ([Boyd, pages 45-46][19] or Rubenstein).

In 383, the Emperor ordered the various non-Nicene sects (Arians, Anomoeans, Macedonians, and Novatians) to submit written creeds to him, which he prayerfully reviewed and then burned, save for that of the Novatians, who also supported Nicene Christianity. The other sects lost the right to meet, ordain priests, or spread their beliefs ([Boyd, page 47][19]).

“The execution of Priscillian and his followers may be cited as typical of the treatment of heretics conditions in that time.” In 384, Priscillian was condemned by the synod of Bordeaux, found guilty of magic in a secular court, and put to death by the sword with a number of his followers ([Boyd, pages 60-61][19] or The Edict of [Thessalonica | History Today][20])

382 Synod Letter

After Theodosius destroyed all resistance, the interpretation of hypostasis as meaning “person,” became official church doctrine:

In 382, the bishops in Constantinople, to argue that their belief is not Sabellianism, sent a letter to the western bishops in which they used the phrase, “three most perfect Hypostases, or three perfect Persons” (Papal Encyclicals).

[8]: https://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0057:entry=ou)si/a [9]: https://revelationbyjesuschrist.com/erickson/ [10]: https://en.wikipedia.org/wiki/Arian_creeds [11]: https://revelationbyjesuschrist.com/arian/ [12]: https://en.wikipedia.org/wiki/Arianism [13]: https://www.fourthcentury.com/second-creed-of-sirmium-or-the-blasphemy-of-sirmium/ [14]: https://en.wikipedia.org/wiki/Acacians [15]: https://www.elpenor.org/basil/letters-3.asp [16]: https://www.elpenor.org/basil/letters-3.asp?pg=39 [17]: https://en.wikipedia.org/wiki/Edict_of_Thessalonica [18]: https://en.wikipedia.org/wiki/Theodosius_I [19]: https://revelationbyjesuschrist.com/boyd/ [20]: https://www.historytoday.com/archive/months-past/edict-thessalonica