Tools for interpreting Christ's saving mysteries in scripture: Aquinas on reduplicative propositions in christology

Abstract This article examines how Thomas Aquinas used reduplicative propositions (e.g. ‘Christ suffers insofar as he is a human being’) to explicate Christ's saving mysteries, or events that Christ did and suffered that produced states of affairs only God can do. Following scripture's focus on Christ as one acting subject, Aquinas argued that we should use the adverbial modifiers ‘authoritatively as God and instrumentally as a human being’ to speak well of Christ's saving mysteries as actions of a single subject. This approach is theologically beneficial because it avoids the pitfalls of thinking of Christ's natures as agents.

. In ST 3.27-59 he treats the life of Christ and the various mysteries. Ibid., DH §558 (translation altered). 8 One can find a recent variation of this critique in Rowan Williams, Christ the Heart of Creation (London: Bloomsbury Continuum, 2018), pp. 86-8. wrong or in error but taking them as a rule for reading scripture can be misleading if it detracts focus from Christ being a single person who acts. Leo's Tome and the conciliar tradition to which it belongs are necessary ontological explanations of what scripture teaches. But in the case of Christ's mysteries, we need more precise language to focus our minds on the person of Christ as the subject of these actions: ones that bear divine and human effects, like Jesus forgiving sins by speaking humanly, as he did for the paralytic.
Thomas Aquinas and his medieval contemporaries developed modes of analysis conducive to a solution. Aquinas used reduplicative propositions, or propositions that include a qualifier like 'as' or 'insofar as', as in the proposition 'X is P qua F', to test the limits of what can be said of Christ's person and actions. Through testing these propositions, we can better understand what we should and should not say about Christ's saving mysteries. This article argues that theologians should follow Aquinas' use of reduplicative adverbial modifiers to speak of Christ's saving mysteries. While ontological explanations can create the thought that natures are acting subjects, Aquinas's solution better aligns our thoughts on Christ as the sole subject of these actions.

Scriptural speech and ontological explanations
Scripture is resolutely focused on the thought that Christ is one person. As Aquinas observes, it regularly 'attributes the things of God to that man, and the things of that man to God indistinctly'. 9 Examples include John 1:14 ('And the Word became flesh and lived among us') and also 1 Corinthians 2:8 ('they would not have crucified the Lord of glory'), among others (cf. Acts 20:28). Scripture without fail identifies the eternal Word and the man Jesus Christ as the same person and the sole subject of his human actions, including his mysteries. Thus, how we speak of Christ's mysteries and his two natures should be disciplined by this reality. To this end, Aquinas appeals to the Aristotelian axiom 'acts belong to supposits' (actus sunt suppositorum): actions belong to subjects, not their natures. 10 The Logos is the subject of all his actions and sufferings as a human being. And this axiom does not contradict speech about Christ's two energies, the types of action that correspond to his two natures. For the actions a person can do depend on the nature she has. 11 These logically basic thoughts must discipline how we speak of Christ and his mysteries.
While biblical statements focus on Christ's singularity, the ontological explanations offered in the conciliar tradition give an account of the state of affairs that must be true if what scripture says about Christ is true. 12 For Aquinas, the central explanation of Christ's person is 'hypostatic union', the notion that Christ has a divine nature and a human nature that are united 'according to one hypostasis and suppositum', and this 9 Aquinas, ScG 4.39.1. My interpretation of Aquinas here is heavily indebted to the analysis of Bruce D. Marshall, Christology in Conflict: The Identity of a Saviour in Rahner and Barth (Oxford: Basil Blackwell, 1987), pp. 176-89. Readers would do well to examine his analysis there and the book as a whole for a fuller understanding of these issues. explanation works because it can 'save' (salvari) scripture's meaning. 13 In fact, Aquinas thinks hypostatic union is 'the only way that which scripture hands down about the incarnation can be saved'. 14 Now he is not saying that scripture needs to be 'saved' from incoherence. Rather, given that scripture attributes things of the man Jesus to the Word and vice versa, theology must give a proper ontological account of Christ that renders this way of speaking more intelligible.
If theology's aim is to save the biblical way of speaking about Christ, it must revise ontological statements if they fail to provide the right sense to that way of speaking. For example, according to Aquinas, Nestorians and Catholic Christians agree that Paul's sentence calling Christ 'the Lord of glory' is true (1 Cor 2:8), but they disagree in the sense in which that claim is true. Aquinas characterises Nestorian belief as the notion that there are 'two hypostases or supposita in Christ'. 15 And for him, this belief does not fit with scripture's language about Christ. For the Gospel of John teaches that the Word, a divine person, became flesh (John 1:14). Nestorius did not understand the Evangelist's statement about Christ, Aquinas argues, because he thought the Son of God was united to a man so that more than one person resulted. 16 Yet scripture plainly says that one person, the Word, became flesh, so that only one person results. So if Nestorius thinks there were two persons in Christ, then he undercuts the language of scripture: if he is right, 'then what the Evangelist says is not true'. 17 Although Aquinas does not say this explicitly, the language of hypostatic union, two wills and two energies in Christ is the only way to explain what scripture says about Christ, for it specifies that he is one person and that divinity and humanity are present and distinct in him. For as Augustine trenchantly noted, scripture insists that this one person exists in two 'forms'the form of God and the form of a servant, and the letter to the Philippians warrants this directly (Phil 2:6-11). 18 Beyond the conciliar tradition, John Damascene and Pseudo-Dionysius before him offered influential explanations of how Christ's human actions save. In his On the Orthodox Faith, the third part of his Fount of Knowledge, John Damascene paired Leo's dictum with Pseudo-Dionysius' famous yet controversial 'new theandric energy' to explain what must be the case in Christ for his human actions to be saving. 19 For John, Christ saves us by means of his instrumental humanity, which is truly his instrument because his human energy exists in a 'connection' (Greek synaphēs) with his divine energy. 20 Like many patristic writers before him, he invoked the iron and fire analogy to explain this connection. Just as an iron blade glows red as it contacts fire, so too does Christ's humanity get the power to drive out sin and death by divine power. 21 But in this connection, neither iron nor fire become the same thing, eliding their natural distinction. So it is with Christ's two natures and energies. And Christ's two energies concur to a single 'theandric action' narrated in scripture, which is a complex state of affairs comprised of a human end-product and a divine end-product. 22 To take one example: when Jesus heals the deceased child, he takes her by the hand humanly and restores her to life divinely, so that she is raised from the dead (Luke 8:54-5). The two end-products of his two energies are the touching and the healing, and these concur to one state of affairs, the resurrection of this girl.
These explanationsconciliar and notfocus on Christ's two natures and energies as sources of action. And they inform how we think of Christ's mysteries narrated in scripture in that, in these events, both of his energies are implicated. To read scripture this way does not create two acting subjects. John Damascene reminds us that sometimes we have to speak of the two natures in Christ, and other times of his person. We can do this, after all, because 'the two natures are one Christ and the one Christ is two natures'. 23 In both cases, we speak of the natures insofar as the Logos, a single person, possesses them. To say, then, that Christ acts according to his human nature alone in walking to Jerusalem and according to both natures in raising the girl from the dead refers to acts of the same person. But questions remain. Scripture teaches that Christ suffers 'according to the flesh' (1 Pet 4:1). But since his fleshly suffering brings about our salvation (cf. Rom 3:21-6), and so it counts as one of Christ's mysteries, does he act in that suffering according to both natures? We might jump to the deliverances of recent literature defending divine impassibility and think 'no'. 24 Christ's divine energy is exempt from his human suffering. Does it follow that Christ's death does not save us? Does each form in Christ really do what is proper to it in communion with the other in a connection, as the Damascene explained? Following Leonine grammar, we could suppose that one nature of Christ 'acts' in the suffering on the cross and the other 'acts' by destroying sin and death in that suffering. Yet according to Chalcedon and Cyril, Christ in scripture is one person and speaker. 25 This solution does not attract the mind to a single acting subject but focuses on Christ's two energies or sources of action. To take these explanations as a rule for reading scripture can be misleading if it detracts focus from Christ being a single person who acts. We need a better way to speak of Christ's saving mysteries that focuses on Christ as the sole subject of these actions.
Adjudicating these matters is difficult because, as Aquinas observes, the realities to which scripture and these ontological explanations refer are divine, and human beings do not have the capacity to describe or explain these realities exhaustively. In his disputed question On the Union of the Incarnate Word, written near the end of his life, Aquinas explains why various christological heresies fail and defends the concept of 'hypostatic union'. This union, he says, can best be compared to the union of soul and body: 'among created things no example of this union is closer than [this one]'. 26 He ends his analysis on an epistemically sombre note.
But all of these examples are deficient … this is a certain singular union above all other modes of union known to us. For just as God is goodness itself and being itself, so also is he unity itself by essence. And therefore, just as his power is not limited to those modes of goodness and being which are in creatures, but he can make new modes of goodness and being unknown to us, so also by his infinite power he can make a new mode of union, so that human nature would be united to the Word personally, and not accidentally, although no example of this could be discovered among creatures. 27 Aquinas had a strong sense that the hypostatic union could not be fully explicated because it transcends human knowledge, both natural and graced. He was likely following Cyril, who argued that the union 'according to hypostasis' (kath' hypostasin) was accomplished 'inexpressibly' (aphrastōs) and 'inconceivably' (aperinoētōs). 28 Now God has revealed the incarnation in scripture, and the ancient church acting in council taught that the mode of union in Christ is 'hypostatic union'. 29 Thus, we can describe it with these concepts, but we should not be surprised when ontological explanations of Christ's two natures fail to describe their object satisfactorily. As nearly every student of christology is aware, christological explanations can become increasingly complicated. Not only do post-Reformation treatises on the ubiquity of Christ's humanity come to mind, but this is also true of the controversy over Leo's Tome. 30 These explanations are necessary to guide scriptural reading and Christian worship, especially the Tome, since Catholics, Orthodox and most major Protestant communions accept it as an authoritative document. But if we rely on them to explain scripture, we can lose scripture's central insight: that Christ is one person who accomplishes his mysteries as a human being. These explanations are necessary to save scripture's sense, but they do not solve every problem.

Reduplicative propositions in christology
To discipline our speech about Christ's mysteries, we should attend first to a critical distinction between concrete and abstract terms, used in both trinitarian theology and christology in the ancient and medieval periods. In christology concrete terms refer to the person; and given conciliar standards, they refer to one person. Thus 'Word', 'Logos' and 'Jesus Christ' refer to the same person. Scripture always uses concrete terms as the subject of sentences where Christ acts. Consider an example. The Gospel of Luke says, 'When the day drew near for him to be taken up, he set his face to go to Jerusalem' (Luke 9:51). 'He' here refers to Jesus Christ, whom Chalcedon confesses to be one and the same with the eternally begotten Son of God, the one who took on flesh and dwelt among us (cf. John 1:14). 31 That person, goes to Jerusalem. By contrast, abstract terms refer to Christ's two natures. These are terms like 'humanity' and 'divinity'. Recall that natures are groups of properties that a subject must have to be a member of a class. Thus, natures are not persons, and so not acting subjects. Scripture teaches Christ 'suffered in the flesh' (1 Pet 4:1), that is, he (not his human nature) suffered because he has a nature that makes it possible for him to suffer. But he, the divine Word, is the one who suffers. So we cannot place abstract terms in the subject line of a proposition; we should not say 'the humanity of Christ set his face to go to Jerusalem', since natures do not act, but persons do.
This distinction is important to keep straight, for according to Aquinas, concrete and abstract terms do not have the same 'way of signifying' (modus significandi). For example, the concrete term 'Son of God' signifies the eternal Word who became incarnate; 'Son of God' signifies in the mode of a person who acts. By contrast, 'divine nature' or 'essence' does not signify in the mode of a person, but in the way of an essence. Thus it does not signify an acting subject. We do not say, 'the divine nature became incarnate', but 'the Son became incarnate'. 32 Furthermore, things said of one nature cannot be said of the other. Thus Christ's natures, divinity and humanity, are not the same: '[t]hings which are of one thing properly cannot be truly predicated of another unless they are the same'. 33 In the incarnation, divinity and humanity are not the same, and thus properties belonging to one cannot be predicated of the other. However, concrete termswhich stand for the personcan be predicated of one another, since they refer to the same person. And finally, abstract termswhich stand for naturescan be predicated of various concrete terms, since one person possesses two natures. Thus, divine predicates can be applied to the man Jesus Christ, in sentences like 'this man created the stars', and human predicates can be applied to the eternal Word, in sentences like 'the Word suffered on the cross', since the same person is the subject of both sentences. 34 With these terminological distinctions in mind, Aquinas investigates Christ's 'being and becoming' (esse et fieri) in Summa Theologiae 3.16 by testing the truth of the sentences 'God is man' and 'man is God'. 35 He likely begins with these two because of scripture's focus on the fact that the Word and the man Jesus are the same person. In these test-case sentences, 'God' and 'man' are predicated of one another in the concrete, not abstractly: 'divinity' and 'humanity'. As his analysis reveals, in Christ, the one who is God is the same as the one who is man, so the sentences must be true. other predications, like 'Christ is a creature'. 36 In this case, the sentence as it stands must be false, amounting to Arianism. But we can affirm the sentence is true if we add a qualifier: 'according to his human nature' (secundum humanam naturam). The predication would then be 'Christ according to his human nature is a creature'. The predication works similarly to the way parts are predicated of a whole: parts of a whole are not predicated of the whole without qualification. Rather, parts are predicated of a whole by specifying the respect in which the part belongs to the whole. Aquinas' well-known example is that we do not say 'an Ethiopian is white', but 'an Ethiopian is white according to his teeth'. This type of qualification of a proposition is known as reduplication.
Reduplicative propositions specify the reason why the predicate applies to the subject by using the qualifier 'as' or 'insofar as' (in Latin, secundum quod and its variants). For a particular branch of medieval semantic analysis, or 'modistic' logic, the goal of analysing the logical properties of propositions is to analyse the relation of the terms in those propositions. Logicians seek the semantic properties of terms in a proposition, which specify the relation of the terms. Two modes of this kind of analysis gradually emerged in the twelfth century and developed further in the thirteenth. The first was the theory of signification, which explains 'the capacity of descriptive terms to function as signs', and the second is the theory of supposition, which interrogates the different modes of the use of terms as subject and predicate. 37 Analysis of reduplicative propositions tended to fall in the purview of the theory of supposition: it analyses how the relationship between the terms changes with the modifier added.
Reduplicative propositions include the semantic property of 'the qua-connective', manifested by qualifiers like 'as' or 'insofar as'. These qualifiers specify the sense in which the predicate applies to the subject. 38 Aquinas offers a formal definition of reduplicative propositions in his Commentary on the Sentences: 'That which is reduplicated in some proposition when I say "insofar as" is that on account of which the predicate belongs to the subject.' 39 A reduplication, then, signifies the respect in which the predicate is applied to the subject. A reduplicative proposition can be stated formally as 'X is P qua F', where qua is the reduplicative modifier. For example, in the proposition 'a tree is brown', the reduplication 'insofar as it has a trunk' can be added to specify that on account of which 'brown' applies to 'tree'. In the case of Christ, 'the Lord of glory was crucified' is true, but the reason 'crucified' applies to the subject (the Lord) is his human nature. Thus, the apt reduplicative qualifier to apply to Christ in this proposition is 'insofar as he is a human being' (in Aquinas' way of putting it, secundum quod homo), so that we get 'the Lord of glory was crucified insofar as he is a human being'. 40 And this way of speaking matches scripture's way of speaking: he, a divine person, was crucified, but only in virtue of the flesh he assumed. As already mentioned, Peter prepares his listeners to suffer by reminding them that Christ 'suffered in the flesh' Aquinas, III Sent., d. 10, q. 1, a. 1, r. 40 Thus Christ's passion is to be attributed to him not insofar as he is God, but insofar as he is a human being (Aquinas, ST 3.46.12). See similar predications applied to Christ's subjection to the Father (3.20.1.1), his priesthood (3.22.3.1) and his predestination (3.24.2 c and ad 1), among others.
( pathontos sarki; 1 Pet 4:1). Likewise, for Paul, Christ is a descendant of David 'according to the flesh' (kata sarka) and declared the Son of God in power 'according to the Spirit of holiness' (kata pneuma hagiosunēs) because of his resurrection from the dead (Rom 1:3-4). Other examples include Romans 9:5, Colossians 1:22 and 1 Peter 3:18. 41 Perhaps for this reason, for Aquinas, the predicate term in a reduplicative proposition signifies natures by abstract terms, and not persons. 42 Speaking of Christ's mysteries Near the end of Summa Theologiae 3.16, Aquinas tests the truth of three reduplicative propositions: 'Christ as a human being is a creature' (a. 10), 'Christ as a human being is God' (a. 11) and 'Christ as a human being is a hypostasis or person' (a. 12). For our purposes, I restrict discussion here to his analysis of 'Christ as a human being is God'. First, recall the Gospel episode retold in the introduction. There Christ, as a human being, forgave sins, something only God can do. Does it follow, then, that Christ, as a human being, is God? This is another way of asking whether both natures are involved in this event. According to this test reduplicative proposition, the respect in which 'God' applies to the subject 'Christ' is 'insofar as he is a human being'. Thus, the reason for the truth of the predication 'Christ is God' is that he has a human nature. Is this the right way to speak of Christ's mysteries?
Aquinas concludes that this proposition, understood in this way, is false, for terms in a reduplicative qualifier (in this case, 'as a human being') signify a nature. 43 If we remove the qualifier, we would get 'Christ is God', which is the same as 'Christ is divine'. Thus, if we add the reduplication 'as a human being' back in, we get 'Christ as a human being is divine'. This would be like saying, 'Christ insofar as he is a human being is divine'. But because divinity and humanity are distinct, we must reject this proposition. Now there is a way to take the proposition so that it is true, namely, if we were to add the demonstrative 'this' to 'human being' and get 'Christ as this human being is God'. The demonstrative creates the thought that 'this man', or the person Jesus Christ, and not human nature, is God. 44 And that proposition is true, since the Word and Jesus are the same person. But it is more natural to take the reduplication to refer to the nature, and so as false.
However, one might object that 'Christ as a human being is God' is true because Christ as a human being does things only God can do. 45 Consider his saving mysteries: all of them bear saving power for us. Christ as a human being forgave the sins of the paralytic! Christ, as a human being, does divine things (i.e. 'is God'). Yet Aquinas thinks that this reduplicative proposition fails to describe Christ's saving mysteries. For persons, signified by concrete terms, do actions. Natures do not act. In Christ's mysteries as scripture tells about them, he is the actor. Christ's two natures and energies are principles of action, but they belong to him as to a single subject who alone does the actions narrated in the Gospels. 46 To draw attention to the thought that Christ is one person, Aquinas adopts adverbial modifiers to speak of him as the subject of these mysteries. thoughts on modes of action, which belong to actors. Thus, Aquinas replaces 'Christ as a human being is God' with linguistic tools more focused on the thought that Christ is a single subject.
'The son of God has on earth the power of forgiving sins', not in virtue of human nature, but the divine nature, in which divine nature the power of forgiving sins is established authoritatively (per auctoritatem); yet in human nature it is established instrumentally and ministerially (instrumentaliter et per ministerium). 47