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The Communicatio
Idiomatum in St. Thomas Aquinas
By
Hilaire K. Troyer de Romero
Copyright of Ite ad Thomam © 2012
Introduction
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In
ST III.16, St. Thomas Aquinas
discusses the question of what may be said about Christ. We find this treatment in the Summa situated well after Aquinas’
thorough explanation of the Hypostatic Union because what may be said of Christ
follows directly from the reality of the Hypostatic Union. More specifically, the answer lies in the
concept known as the communicatio idiomatum (or ‘communication of
properties’). This concept refers to an
ontological, and not just logical, reality in Christ. It can be defined as “the mutual exchange of divine and human properties in
virtue of the Hypostatic Union.”[1] As a logical reality, it is sometimes referred
to as the ‘predication of properties’.
Sacred Scripture is replete with practical examples of this concept.[2] Misunderstandings of the communicatio idiomatum have been at the heart of numerous
Christological heresies such as Nestorianism and Monophysitism. In this paper, I shall explain the principal
elements of the communicatio idiomatum as presented by St. Thomas in ST III.16, beginning with its direct
connection to the Hypostatic Union, and then a brief overview of the general
rules that can be gleaned from St. Thomas’ treatment of this issue.
I. Communicatio idiomatum and the Hypostatic Union
In the first article of
question 16, St. Thomas begins his treatment by examining a fundamental
Christological statement, “God is man.”
Here Aquinas establishes the immediate connection between the communicatio idiomatum and the
Hypostatic Union. He says,
Hence,
supposing the truth of the Catholic belief, that the true Divine Nature is united with true Human Nature not only in person, but also in suppositum or hypostasis;
we say that this proposition is true and proper, ‘God is man’ –not only by the truth of its terms, that is, because Christ is true God and true man, but by the truth of the predication.
For a word signifying the common nature in the concrete may stand for all contained in the common nature, as this word ‘man’ may stand for any individual man. And thus this word ‘God,’ from its very mode of signification, may stand for the
Person of the Son of God, as was said in I.39.4.[3]
The “Catholic belief”
referred to here is the Hypostatic Union.
For the sake of clarity I shall review a few key terms found in the text
above. A suppostium or hypostasis is a bearer of properties,
that is, any primary, or individual, substance that subsists in itself. Aquinas refers to the suppositum or hypostasis
as a “subsistence,” rather than as a mere substance, to express the connotation
of “subsisting in itself.”[4] A person is a particular kind of hypostasis or suppositum, namely, an individual substance of a rational nature.[5] If we speak of an ordinary man, such as Aristotle, the suppositum
or hypostasis is Aristotle himself;
and that hypostasis has one human nature. The suppositum is the “who” (the quis
est), namely Aristotle, and the
nature is the “what” (quid est),
namely a man. The two are not identical: Aristotle subsists in the human
nature but we do not say that the nature is Aristotle, since this would
be the same thing as saying that “Aristotle is humanity,” which is patently
false.[6]
In the case of Christ, the suppositum or hypostasis is the quis est,
the Divine Second Person, who subsists in the two natures, which are united
substantially.[7]
The communicatio idiomatum is the logical consequence of the perichoresis, or unity of the two
natures in Christ, that results from the Hypostatic Union.[8] That is, there is a natural interchange of
properties between the two, because of the substantial union whereby the divine
nature penetrates the Human Nature (without changing it) within the one Divine
Personality or hypostasis that we
call the Logos.
Returning to the text at
hand, the proposition “God is man” is a true statement and not merely in an
analogical or metaphorical sense, in the way many heresies have interpreted it,[9] precisely because of this Union of One Person
and two natures. In other words, when
the subject of a sentence refers to the Second Person of the Trinity, it is
possible to predicate of that subject the concrete properties of either nature,
regardless of whether the term in the subject of the sentence connotes the divine
nature or the human nature of Christ. Since the Person of the Son of God for Whom this
word ‘God’ stands, is a suppositum of
human nature this word “man” may be predicated truly and properly of this word ‘God’. Just as it is possible to say that “Socrates is
man,” it is possible to say that “God is man,” when by “God” we mean “The
Second Person.” In
the statement “God is man,” the term ‘man’ is being predicated of the Divine
Person, the Son of God as of the suppositum, and not of the divine nature
itself. This suppositum has both human and divine natures and hence both human
and divine properties. The inverse statement, namely,
“Man is God,” which Aquinas examines in article 2 of question 16, is also true
because the term “man” can refer to any hypostasis
that has a human nature. So it can refer
to the Second Person as the subject who, as I mentioned above, has both human
and divine natures. The statement would
be false, of course, if the term ‘Man’ were to refer to all men, or any man
other than Christ, such as Socrates, because then it would refer to a suppositum that possesses human nature
only.
II.
Corollaries
Throughout question 16, Aquinas examines particular
statements regarding Christ and asks whether or not they are true. The result of his discussion of each
statement is an overall framework, or a set of rules, that govern the communicatio idiomatum. Below I address the primary rules that can be
gleaned from question 16, which follow as logical consequences of the
particulars of the Hypostatic Union.
A. Only Concrete
Terms of Concrete Subjects May Be Predicated of Either Nature
The
most fundamental of these rules arises from the distinction between concrete
and abstract terms, as St. Thomas explains in Article 1. Concrete terms are those that refer to a
property as it exists in a subject (man, carnal, animate, etc.), whereas abstract
terms refer to properties in se, apart from a subject (divinity,
humanity, truth, etc.).[10]
This means that the concrete term will signify the suppositum and abstract terms will signify the nature apart from
the suppositum[11]
Aquinas, in his reply to Objection 2
in Article 1, says,
[I]n
the mystery of the Incarnation the
Natures, being distinct, are not predicated one of the other, in
the abstract. For the divine nature is not the human nature. But because they agree in suppositum, they are predicated of each other in the concrete.[12]
Fr. Garrigou-Lagrange
formulates this rule thus:
[C]oncrete words of concrete subjects, both of natures
and properties, generally speaking, can of themselves be predicated of either
[nature]; but abstract words of abstract subjects cannot of themselves formally
be predicated of either.[13]
In other words, because concrete terms directly signify the suppositum
and only indirectly the nature, they may be predicated of both the divine and human
natures of Christ. Abstract terms, however, may only be predicated of both
natures when they refer to divine properties, because only in the divine nature
is there an identity between its properties and the nature itself. For example, we may say that “Christ is
Truth,” because the Second Person by virtue of His Divinity is indeed Truth
itself. But we cannot say that “Christ is humanity” because in this case, the
abstract term “humanity” is not identical with the divine suppositum.[14]
B. Reduplication Limits
the Concrete Term to One Nature
Another general rule is that we must exercise great care when
there is an instance of reduplication such as in the statement, “Christ, as man
is a creature.” In such instances the reduplication limits the concrete term to
one particular nature so that what is predicated must be true of that nature by
itself.[15]
For example, in article 10, Aquinas examines
the truth of the statement, “Christ, as man, is a creature.” Here he affirms
the statement because the reduplication “as man” means the concrete term
“creature” refers to the human nature specifically, which is indeed created.
It must however be borne in mind that the term covered by the
reduplication signifies the nature rather than the suppositum, since it is added as a predicate, which is taken
formally, for it is the same to say “Christ as Man” and to say “Christ as He is
a Man.” Hence this is to be granted rather than denied: “Christ as Man is a
creature.” But if something further be added whereby [the term covered by the
reduplication] is attracted to the suppositum,
this proposition is to be denied rather than granted, for instance were one to
say: “Christ as ‘this’ Man is a creature.”[16]
Following the same guideline, in article 11,
Aquinas points out that the statement “Christ, as man, is God” would be
false, because the reduplication limits the concrete term “God” to the human
nature alone which, though possessed by God in the Second Person, is not
identical to God. In some instances, the
reduplication adds clarification, as in the first example found in article 10,
and in others it makes an otherwise true statement false—as seen with the
example from article 11.
C. Essential Properties of the Divine Nature Must Not be
Predicated denominatively of Christ
A third rule is that adjectival
names, in the concrete, that are derived cannot always be accurately predicated
of Christ. For example, we cannot call Christ “lordly.” [17]
Aquinas says in ST III.16.3:
Now ‘God’ and
‘Lord’ are predicated essentially
of the Son of God; and hence they
ought not to be predicated denominatively, since this is derogatory to the
truth of the union. Hence, since we say ‘lordly’ denominatively from ‘lord’, it
cannot truly and properly be said that this Man is lordly, but rather that He is
Lord. [18]
In
other words, to call Christ ‘lordly’ would imply that He is not God because, to
use the word ‘lordly’ with respect to Christ, either (a) is not fitting to Him
who is Lord of Lords and therefore derogatory, and fails to show a true belief
in the Hypostatic Union, or (b) is indicative of mere god-likeness, which is
heretical, as the Church has already decreed many times since its condemnation
of Arianism.
D. Phrases that Sound
Heretical Should be Avoided
Although the communicatio
idiomatum does provide us with a great amount of freedom with regard to
what we say about Christ, St. Thomas warns us against those statements that may
be technically true but that can easily be interpreted in a heretical way. For example, if we were to say, “Christ is a
creature,” we run the risk of sounding like the Arians, who believed Christ was
completely created and, therefore, less than the Father. If what we mean to say is that Christ’s human
nature is created, it would be better expressed with a clarification, such as
that which Aquinas suggests in article 8: “And hence we must not say absolutely
that Christ is a ‘creature’ or ‘less than the Father’; but with a
qualification, viz. ‘in His human nature’."[19] In all cases, our use
of language concerning Christ must be faithful to the reality of the Hypostatic
Union. Those predicates that appear
ambiguous should always be clarified so as to avoid heretical interpretations. It is always of the utmost importance that
the language we use display logical congruence with the Hypostatic Union and
the divinity of Christ. Aquinas says,
“As Jerome [Gloss, Ord. in Hosea 2:16] says, ‘words spoken amiss lead to
heresy’; hence with us and heretics the very words ought not to be in common,
lest we seem to countenance their error.”[20]
Conclusion
In sum, the communicatio
idiomatum is simply a consequence of
the Hypostatic Union. Because the two
natures in Christ are united in the one suppositum,
the Son of God, we may predicate what belongs to one nature of the other in the
concrete. Yet the two natures are not intermingled or confused, so we must
always ensure that the rules discussed above are always observed, so as not to
imply a lack of unity or a confusion of the natures in Christ. Joseph Pohle summarizes the communicatio idiomatum as a logical
reality thus:
Formulated in logical terms, the ontological law underlying the communicatio idiomatum gives us the following rule of predication: “Whatever is
predicated of the Divine Person of Christ according to His Divine Nature, can
and must be predicated of the same Divine Person also in His human nature, and vice versa; but the predicates proper to
the Divine Nature must not be assigned to the human nature, and vice versa.” The first part of this rule
is based on upon the unity of the one Divine Person in two natures; the second,
upon the fact that the two natures co-exist separately and in-confused in one
Person.[21]
It is on the basis of this
principle that the Church was able to develop her Christological doctrine and
combat the heresies that have so relentlessly assailed her. St. Cyril of
Alexandria in his third letter to Nestorius, expresses this in a profound way:
For we do not divide up the
words of our Saviour in the gospels among two hypostases or persons. For the
one and only Christ is not dual, even though he be considered to be from two
distinct realities, brought together into an unbreakable union. In the same
sort of way a human being, though he be composed of soul and body, is
considered to be not dual, but rather one out of two. Therefore, in thinking
rightly, we refer both the human and divine expressions to the same person. For
when he speaks about himself in a divine manner as “he that sees me sees the
Father,” and “I and the Father are one,” we think of his divine and unspeakable
nature, according to which he is one with his own Father through identity of
nature and is the “image and impress and brightness of his glory.” But when,
not dishonouring the measure of his humanity, he says to the Jews: “But now you
seek to kill me, a man who has spoken the truth to you,” again no less than
before, we recognise that he who, because of his equality and likeness to God
the Father is God the Word, is also within the limits of his humanity. For if
it is necessary to believe that being God by nature he became flesh, that is
man ensouled with a rational soul.... All the expressions, therefore, that
occur in the gospels are to be referred to one person, the one enfleshed
hypostasis of the Word. For there is one Lord Jesus Christ, according to the Scriptures.[22]
Bibliography:
Council of
Ephesus.
Garrigou-Lagrange,
Reginald. De Christo Salvatore.
Turin: R. Berruti, 1948. <http://www.ewtn.com/library/theology/christ.htm>
Ott, Ludwig. Fundamentals of Catholic Dogma. St.
Louis: B. Herder, 1964.
Pohle, Joseph;
Arthur Preuss (trans., ed.). Christology:
A Dogmatic Treatise on the Incarnation. St. Louis: B. Herder, 1916.
Tanquerey,
Adolphe. A Manual of Dogmatic Theology.
Translated by John J. Byrnes. New York: Desclee Company, 1969.
The Holy Bible (Douay- Rheims Version). London: Baronius
Press, 2003.
Thomas Aquinas,
Saint. Summa Theologica. Notre Dame, IN: Ave Maria Press, 1981.
[2] Cf. John 8:58; Acts 3:15, 2:8; Romans 8:32, 6:3; I
Cor. 2:8;
[3] Summa theologiae (henceforth,
ST) III.16.1.
[4] Cf. ST I.29.2c:
“In another sense substance means a subject or suppositum, which subsists in the genus of substance. To this,
taken in a general sense, can be applied a name expressive of an intention; and
thus it is called suppositum. It is
also called by three names signifying a reality—that is, “a thing of nature,” “subsistence,”
and “hypostasis,” according to a threefold consideration of the substance thus
named. For, as it exists in itself and not in another, it is called “subsistence”;
as we say that those things subsist which exist in themselves, and not in
another.”
[5] Cf. ST I.I.29 Aquinas sometimes uses the term hypostasis to include the concept of “rational nature.” It seems
that the terms suppositum, hypostasis, and person, are used interchangeably.
[6] Cf.
ST III.2.2c.
[7] This by the grace of union that imparts the Personal Being
of the Word on the human nature of Christ. Cf. Adolphe Tanquerey, A Manual of Dogmatic Theology, Vol. 2,
p. 28.
[8] Cf. Pohle & Preuss, p. 184:
“Though practically identical with Perichoresis, the Communication of Idioms
may more appropriately be regarded as an effect thereof.”
[9] St. Thomas references the errors of Photinus and Nestorius
specifically in ST III.16.1.
[10] Adolphe Tanquerey, A
Manual of Dogmatic Theology, Vol. 2, p. 28.
[11] Cf. Ludwig Ott, Fundamentals of Catholic Dogma, p. 161: “communication idiomatum fit in concreto, non
in abstracto.”
[12] ST III.16.1. Cf.
article 5: “Now
concrete words stand for the hypostasis of the nature;
and hence of concrete words we may predicate indifferently what belongs to
either nature--whether
the word of which they are predicated refers to one nature,
as the word “Christ,” by which is signified “both the Godhead anointing and the
manhood anointed”; or to the Divine Nature
alone, as this word “God”
or “the Son of God”; or to the
manhood alone, as this word “Man” or “Jesus.”
Hence Pope Leo says (Ep. ad Palaest.,
cxxiv): “It is of no consequence from what substance
we name Christ;
because since the unity of person remains inseparably, one and the same is
altogether Son of Man by His flesh, and
altogether Son of God by the Godhead
which He has with the Father.”
[13] Garrigou-Lagrange, Christ
the Saviour, Ch. 18, Subsection: “The Consequences Of The Union As Regards
Those Things That Belong To Christ In Himself”.
[14] Ibid.: “It must be observed concerning this
communication that concrete names, such as God, man, in opposition to abstract
names, such as Godhead, humanity, signify directly the suppositum, and indirectly the nature. For “God,” signifies the suppositum that has the divinity, and “man”
signifies the suppositum that has the
humanity. If, therefore, the suppositum
is the same for the two natures, then it is true to say: “God is man,” although
it is false to say: “The Godhead is the humanity.” Thus we shall see that the
generally accepted rule, namely, concrete words of concrete subjects, both of
natures and properties, generally speaking, can of themselves be predicated of
either; but abstract words of abstract subjects cannot of themselves formally
be predicated of either. Thus we shall see that we cannot say the Godhead is
the humanity or that God is the humanity, or that the humanity is God. Therefore we
must take great care to distinguish between abstract terms and concrete terms.
The abstract term signifies the nature separated from the subject, for example,
humanity. The concrete term signifies the nature as existing in the subject,
for example, man. Hence this distinction between concrete and abstract term is of
great importance in distinguishing between the nature and the suppositum, since the nature is an
essential part of the suppositum.
There is the same distinction between “being” as a noun and “being” as a
participle, or between the reality and the real itself.”
[15] Ludwig Ott, Fundamentals of Catholic Dogma, p. 161.
[16] ST III.16.10.c.
[17] Adolphe Tanquerey, A
Manual of Dogmatic Theology, Vol. 2, p. 28.
[18] ST III.16.3; cf., Pohle & Preuss, pp. 188-189;
Adolphe Tanquerey, A Manual of
Dogmatic Theology, Vol. 2, p. 28.
[19] ST III.16.8c.
[20] Ibid.
[21] Pohle & Preuss, p. 186.
[22] Council of
Ephesus, “Letter of Cyril to Nestorius” (Cum
salvator noster).
