In Karen Kilby’s article ‘Aquinas, the Trinity and the Limits of understanding’, she argues that Aquinas is consciously apophatic in his way of speaking about God, because of the way in which he treats certain technical aspects of Trinitarian doctrine. According to Kilby, Aquinas “is not trying to give us insight” about the inner life of God, but is quite deliberately “articulating a lack of insight”. Kilby’s article falls short of embracing a full-blown apophaticism, but the apophaticism which she attributes to Thomas is in her view a strength which she commends as a respectable position for theologians to take in respect of the Divine mysteries.
At times, Kilby appears to come close to anti-realists such as Cupitt or D.Z.Phillips in acknowledging that the doctrine of the trinity “can have an important grammatical and structural role within Christianity whether or not it carries any insight.” Rather like the poem ‘Jabberwocky’ by Lewis Carroll, Kilby argues that “we have a grammar for speaking of God, but no accompanying understanding.” However she distances herself from a radical application of this approach more generally in theology, while remaining ‘sympathetic’ of those who do.
In this article I will attempt to argue that although Aquinas is informed by a long tradition of apophatic theology, he nevertheless makes a clear disjuncture from this tradition in at least three important ways, namely his distinctive doctrine of analogy, his emphasis on God’s revelation in Scripture and consequently his controlling hermeneutic of the plain sense of Scripture. Where Thomas runs into incoherence arises precisely where he attempts to square the circle of marrying the neo-Platonic doctrine of Divine simplicity with the Christian doctrine of the trinity. Contrary to his progressive instincts, Aquinas retreats back into apophaticism at this point because there is logically nowhere else for him to go.
The apophatic tradition.
Apophatic or negative theology (via negativa), dominant in the Eastern traditions of the Christian church and popularised through such writers as Pseudo-Dionysius, Maimonides, Gregory of Palamas, Nicholas de Cusa and St John of the Cross stresses the dissimilarity of God’s essence to our language about him. According to this view, the best we can say about God is what God is not rather than what God is. We cannot say that God is wise, but we can say that He is not stupid! This is the via negativa and appears to be endorsed in the prologue to Summa Theologiae. “We cannot know what God is, but only what He is not. So to study Him, we study what He has not -- such as composition and motion”. Alternatively and with more sophistication, we can resort to paradox: ‘neither x nor y’ but ‘beyond x and y’ (where x and y refer to attributes of God such as wise, good, atemporal etc.). This is the apophatic way, in that it is stressing not only the negative but also the apo, the beyondness of God to human discourse. Gregory of Nazianzus for instance compares himself to Moses ascending the Mount and hiding in the cleft of the Rock (Christ) before seeing God’s back parts only.
It is probably fair to say that all theology is apophatic in one sense: God is infinitely more than our understanding and our language about him can ever be. God can never be reduced to our human concepts of Him. He dwells in unapproachable light. The Cappodocean Fathers rightly draw us to a reverent humility and awe before the eternal Majesty of the Almighty. Yet it should also be remembered that unlike Moses with whom Gregory compares the believer, we have not come to Mount Sinai but “to Mount Zion, the City of the living God..to Jesus the Mediator of the new covenant”. (Hebrews 12: 18, 22-24), the Mount, let us say, of revelation. In the words of Saint Paul, we may ‘see through a glass darkly’; nevertheless, this at least means that ‘ we know in part’. I will discuss this qualification of apophaticism in more detail below in the section of Aquinas on revelation.
The Eastern tradition has a stronger definition of apophaticism than much Western theology would allow. It means total agnosticism regarding the ‘essence’ or nature of God. Pseudo-Dionysius, a leading articulator of this position in the 6th century famously applies apophasis even to God’s existence. “It (God) is the universal cause of existence while itself existing not, for it is beyond all being” This is of course true if one means that God’s existence is necessary whereas creaturely existence is merely contingent. More contentiously however, and reminiscent of Buddhist thinking, Pseudo-Dionysius asserts that “the divine unity is beyond being…the indivisible Trinity holds within a shared undifferentiated unity……..the assertion of all things, the denial of all things, that which is beyond every assertion and denial.” Similarly in The Mystical Theology he writes concerning the Cause of all being that:
“we should posit and ascribe to it all the affirmations we make in regard to beings, and more appropriately, we should negate all these affirmations, since it surpasses all being. Now we should not conclude that the negations are simply the opposites of the affirmations, but rather that the cause of all is considerably prior to this, beyond privations, beyond every denial, beyond every assertion”
In this he parts company with Aristotle who argued that negations are the opposite of affirmations. For Pseudo-Dionysius, God is beyond antithesis, logic and the law of non-contradiction. In this respect he finds new resonance in Continental and postmodern philosophy influenced by Hegelian synthesis and the Nietzschean rejection of binary opposites. So for example Sartre sounds remarkably Dionysian in Being and Nothingness when he writes: “Being is equally beyond negation as beyond affirmation.”
Aquinas, in contrast, (following Augustine), understood the laws of logic as necessary truths within the Divine mind: “necessary truths are eternal only because they exist in the eternal mind; nothing besides God is eternal.” God is the Necessary Truth (John 14:6) on which logic depends. That is because He is the Logos (John 1:1). God can make no denial of himself (2 Tim 2:13) and cannot lie (Num 23:19; John 8:44-45). That is why, for Aquinas, there is no final conflict between the truths of faith and the truths of reason. The principles of reason have been Divinely implanted in us.
In the so-called ‘Euthyphro’ dilemma, raised in Plato’s book by the same name, Socrates raises the puzzling riddle of whether something is pious or good because the gods command it or alternatively whether the gods command it because it is good. The same dilemma could be restated: ‘Does God follow the law of non-contradiction as a standard higher than himself or is it only a law because God says so?’ Aquinas’ answer to both forms of the riddle was that God does not have goodness, reason or logic as separate qualities in the way that human beings do. God has no composite qualities. He is absolutely Simple. It follows therefore that, for God, to be is to be logical. He is his own goodness and love, reason and logic. The Word (Logos) was God (John 1:1). As Aquinas later expresses it: “..there is nothing in God that is not the divine being itself.” Later I will suggest another way that Aquinas could have addressed the Euthyphro dilemma without resorting to a strong version of Divine Simplicity.
Thomas’ doctrine of analogy
“Of him (God) there is neither name or opinion”, and later "negations about God are true; but affirmations are vague (or, according to another translation, ‘incongruous’).".
Thomas, like many in his day, mistakenly believed Dionysius to be a first century convert of Paul with apostolic authority: It is all the more remarkable therefore that Thomas finds his position inadequate: “True affirmative propositions can be formed about God”, he counters, for example the affirmative proposition that ‘God is three and one’ or that he is ‘omnipotent’. Aquinas refers to positive theological statements in Scripture such as “The Lord is a great warrior: Almighty is his name” (Exodus 15:3). Church fathers like Augustine similarly applied positive predicates such as ‘strong’, ‘wise’ and ‘being’ to God. It is clear then that the famous quotation from Aquinas in the Summa’s Prologue “We cannot know what God is, but only what He is not,” which Ward, McCabe and others use to defend a strong apophatic reading of Aquinas is not straightforwardly obvious in its meaning, and must be qualified.
Since Aquinas had a more Aristotelian view of logic in his theology than Dionysius, it would be a fallacy, he reasons, to apply words such as ‘strong’, ‘wise’ and ‘being’ to God in an equivocal sense. This is a question still faced by Wittgensteinian fideists and anti-realists. If God-talk is equivocal, why should we use these particular words rather than entirely opposite words or else no words at all? One can only fall back on the arbitrary authority of tradition in establishing the ‘grammar’ of theology, once a ‘correspondence’ account of truth has been abandoned.
This does not mean that Aquinas naïvely accepts that human language can be applied univocally (i.e. in exactly the same way) with respect to the infinite, transcendent God. All human use of language derives from finite creaturely experience. God, in contrast, has a different mode of being to creatures, since there is nothing in Him which is not Divine. This amongst other reasons, makes univocality impossible.
So, if language about God cannot be applied in the same way as language about the world (univocal), but neither can be applied in an entirely different way (equivocal), there appears to be logically only one possibility left, namely that language must have a similar meaning when applied to God. One example of using terms similarly would be using the predicate ‘bright’ to describe both the sun and a painting. The painting is bright in a similar (but immeasurably inferior) way to the brightness of the sun. Aquinas calls the relationship between the two senses ‘analogical.’ He justifies this similarity primarily on the grounds of a diminished participation of the creature in its Creator. That is why A.N.Williams sees in this doctrine of analogy an essential component of Thomas’ understanding of the goal of existence: namely participation in the Divine Nature, to be fulfilled in the beatific vision. Though Pseudo-Dionysius also speak of the Divine by way of analogy and metaphor, noone previously had clarified the concept as clearly as Aquinas did. It is his lasting contribution to the religious language debate.
Yet, some critics have accused Aquinas of being incoherent here. They argue that an analogy can only work by presupposing some univocal correspondence, otherwise it reduces again to an equivocation. The critics are correct, nevertheless Geisler suggests that Aquinas has already addressed this problem. Analogy does imply univocality to some extent, but this univocality is not in the realm of being, but in the realm of concepts and definitions. Aquinas is saying that concepts have the same definition for both humans and Creator but that they are applied differently. (So God’s love is unlimited and perfect in contrast to human love). Aquinas explains:
“ In names predicated of many in an analogical sense, all are predicated because they have reference to the same one thing; and this one thing must be placed in the definition of them all.”
He illustrates this principle with the example of the term ‘wise’:
“Thus also this term "wise" applied to man in some degree circumscribes and comprehends the thing signified; whereas this is not the case when it is applied to God; but it leaves the thing signified as incomprehended, and as exceeding the signification of the name. Hence it is evident that this term "wise" is not applied in the same way to God and to man.”
Aquinas concedes along with the apophatic tradition that our intellect “cannot see Him (God) as He is in Himself”, or at least not in this life, but he draws different conclusions from the mystics by maintaining that the intellect “knows that one and the same simple object corresponds to its conceptions”. Just as we are able to understand lower material objects in a non-material mode while still affirming intellectually that they are in themselves material, so according to Aquinas, we can understand transcendent concepts such as God being simple, even though our mode of understanding him is composite.
For Aquinas then the via negativa comes into its own qualified and legitimate sphere in refining how concepts may or may not be applied to God, having stripped them of their empirical limitations. Only the perfection is to be applied and not the finite mode of signification. This means that creatures can have the same characteristics as God (eg goodness), but not in the same way that God has them. God has them in ‘the mode of supereminence’. Aquinas adds that: “all perfections exist in creatures dividedly…and in God unitedly.”
Thomas’ doctrine of analogy points to the understanding that God cannot be known infinitely or exhaustively, for then humans would have to be omniscient, yet God can still be known truly. This reading harmonises Thomas’ insistence that:
“it is clearly impossible for any created intellect to know God in an infinite degree. Hence it is impossible that it should comprehend God” and that the name God is incommunicable. 
with his later qualification of this statement:
“this name God is communicable, not in its whole signification, but in some part of it by way of similitude…” Likewise, God is comprehensible to believers in contrast to ‘non-attainment’ but is incomprehensible in terms of ‘being included in the one comprehending.’
Thus the apophatic proof text found in the prologue to the Summa Theologiae: “We cannot know what God is, but only what He is not,” should be contextually interpreted as meaning we cannot know anything about God in this life univocally but only either negatively or analogically. The more accessible work, Summa Contra Gentiles, makes this clearer. In the context of a discussion on names of perfections used in the mode of supereminence, Aquinas uses the similar proposition to the Summa Theologiae: “We cannot grasp what God is, but only what he is not” except that, significantly here Aquinas adds the qualifying phrase, “and how other things are related to him.”  which signals a reference back to his doctrine of analogy.Thomas on revelation
Whether or not we can speak adequately about God in human language is inseparably connected with the question of whether or not God has spoken adequately to us in human language. This is the second disjuncture I note in Aquinas from absolute apophaticism: i.e. Aquinas’ emphasis on God as a God of revelation. If God has used language to communicate to us then it follows that this human language must be adequate to convey truth about God. Words about God may be anthropomorphic, but “God has anthropomorphised himself”, thus bridging the finite/infinite gap. In Summa Contra Gentiles, Aquinas concludes a chapter on reason and faith with a quotation from Paul:
“So the things that are of God no man knoweth but the the Spirit of God. But to us God hath revealed them by His Spirit.”
Furthermore, humans are theomorphic, made in the image of God, resulting in an ontology of participation. As previously noted, Thomas anticipates an ultimate climax to this participation in a full eschatological participation in the Divine nature leading to deiformity. God changes and indwells the intellect of the redeemed, making their knowledge like his own. “When any created intellect sees the essence of God, the essence of God itself becomes the intelligible form of the intellect.”
Thomas Aquinas was known as magister in sacra pagina (Master of the sacred page). He was devoted to the study of Scripture. As a Dominican friar he was required to expound the sacred writings between one and four times a week and as a Master Teacher his duty was to read the text to his pupils explaining its sense and application.  This resulted in his writing numerous commentaries as well as the famous Catena aurea (Golden Chain) of the four Gospels.
Aquinas’ devout practice embodied his profound conviction that the Bible is God’s revelation to humanity. “Revelation is the basis of sacred scripture” he wrote, since “The author of Holy Scripture is God” Curiously, a modern scholar of Aquinas seems to overlook this fact and instead project his own Barthian understanding of Scripture onto Aquinas:
“For Thomas, then, Scripture is not of itself revelation so much as the bearer of revelation, rather as in a dependent way (dependent upon both God and Scripture), the church is the bearer of revelation, too”
In contrast to this neo-orthodox view of the Bible as a human witness to the Word, however, Aquinas insisted that the Bible is ‘Divinely inspired Scripture’, quoting 2 Timothy 3:16 (‘All Scripture is inspired by God’). Without this revelation, Aquinas points out that God’s truth would only be known by a few and would be mixed with much error. Furthermore, in discussing the relationship of sacred knowledge in scripture to the other sciences, Aquinas teaches: “Sacred doctrine derives its principles not from any human knowledge, but from the divine knowledge, through which, as through the highest wisdom, all our knowledge is set in order”. This does not preclude the fact that for Aquinas God has also revealed himself in nature (a point also accepted by Dionysius), but that some truths, for example the truth of the incarnation or that ‘God is trinity’, can only be accessed through special revelation. Although there are ‘vestiges’ of the trinity in nature, natural revelation and unaided reason are insufficient for arriving at this truth.
Again, unlike the later Barthians, Aquinas held to the inerrancy of scripture: “nothing false can underlie the literal sense of Scripture”. Concerning the books of Scripture, he writes, “I firmly believe that none of their authors have erred in composing them” Indeed, “It is heretical to say that any falsehood whatsoever is contained either in the gospels or in any canonical scripture.”
None of this sits easily with the Neo-Platonic roots of apophaticism. Plotinus (d AD 270), the father of neo-Platonism, described a hierarchy of being descending from the ineffable One who is wholly other to the base world of matter. There is no conception of the One revealing (him)self in neo-Platonism. The One is rather beyond all knowledge and being. “The One is in truth beyond all statement”. Even the title ‘One’ is only a negation of plurality. “If we are led to think positively of the One, name and thing, there would be more truth in silence.” Anticipating Kierkegaard, Plotinus writes of the necessity of transcending reason in order to ‘know’ this One: “only by a leap can we reach to this One which is to be pure of all else.” Hence self-authenticating mystical experience is privileged over reason within this tradition.
On the one hand Thomas remains tied to neo-Platonism in his belief that God cannot be known in his ‘essence’, but only through his ‘effects, either of nature or of grace’ yet begins to free himself from these strictures in his Christian confession of a God who has made himself known in the person of Jesus Christ who himself used human language to communicate God’s mind.
Thomas on the plain sense of Scripture
A third important way in which Aquinas began to break from previous apophatics was his emphasis on the plain meaning of the text of Scripture. Consistent with Aquinas’ dual basis of the analogical nature of religious language and the fact of propositional revelation, it is unsurprising that Aquinas also insists upon the intelligibility of God’s written revelation.
Later reformers such as Luther and Calvin criticised mystical writers of the middle ages such as Pseudo-Dionysius (‘whoever he may have been’), for their fanciful allegorisation of Bible passages, insisting instead upon “the proper and simple sense of Scripture”. Yet Aquinas should be credited with paving the way for this approach. Just as the speculative allegorisation of texts by the mystics was entirely consistent with their presuppositions regarding the mystery of the Divine being and the inadequacy of human language to describe him; conversely Aquinas with his presupposition of the Bible as revelation in analogical language followed this through consistently with his insistence on the plain meaning of the text as the controlling sense.
One may also note the link here between Pseudo-Dionysius’ allegorisation of Scripture and his hierarchicalism. Dionysius is credited with coining the term ‘hierarchy’; it is so central to his thinking, and occurs in the title of two of his works. His ecclesiastical hierarchy corresponds closely to Plato’s political hierarchy headed up by the Philosopher-King. In his book, The Celestial Hierarchy, Dionysius explicitly segregates the enlightened ones from the common masses:
“it is most fitting to the mysterious passages of scripture that the sacred and hidden truth about the celestial intelligences be concealed through the inexpressible and the sacred and be inaccessible to the hoi polloi. Not everyone is sacred, and, as scripture says, knowledge is not for everyone.”
It must be conceded that Aquinas, as a man of his time was not immune to an hierarchical worldview. He still admired Pseudo-Dionysius (falsely considering him apostolic) and answered a question himself with eight articles to the hierarchical ordering of the nine choirs of angels. Nevertheless, one can see a radically new direction emerging in Aquinas when he observes that natural reason alone, without ‘supernatural inspiration as an object of belief’, would have the ‘awkward consequence’ that ‘few men would possess the knowledge of God.’ Aquinas’ emphasis on the plain sense of Scripture blew open the door for the later Reformers to champion the democratisation of the knowledge of God 
Karen Kilby is also concerned to avoid ‘privileging the theologian.’ She associates a graspable understanding of (Trinitarian) doctrine with the social Trinitarians and acknowledges this as a possible solution. Her sensibilities however incline her to level things out for the ordinary believer in the admission of absolute mystery for all. My contention is that this does not appear to be Aquinas’ initial methodology, but I will qualify this claim in my conclusion.
Modern exponents of a plain sense of Scripture are often portrayed as doing ‘violence’ to the text of Scripture by insisting on a ‘singular’ meaning. However, this would be a straw man argument if applied to Aquinas. Aquinas accepts that “in Holy Scripture a word may have several senses.” As a result he is not dogmatic in favouring say an interpretation of Augustine as opposed to Basil or other eastern fathers.The different senses may include for example a typological, moral or eschatological sense. Together they may present a ‘sensus plenus’, yet the important thing for Aquinas is that the primary and controlling meaning remains the literal meaning.‘Literal’ did not carry for Aquinas the same wooden connotation as it does for us. He incorporates within this term a place for symbolism and poetry. ‘Literal’ is really just another way of referring to the plain sense intended by the author. So, for example “When Scripture speaks of the arm of God, the literal sense is not that he has a physical limb, but that he (literally) has what it signifies, namely the power of doing and making,” The word ‘author’ is itself an ambiguous term which in Aquinas’ hermeneutic does not always refer to the human author’s intention, but sometimes what he sees as the Divine Author’s intention (eg in Messianic applications of Old Testament prophecies). Nevertheless, for Aquinas, the key to the plain sense of Scripture is it’s original historical sense, so for example, the Red Sea crossing, the events of Jesus’ life, death and resurrection and (alien to modern thinking) the narrative of Adam and Eve which he also accepts as a space-time event. Aquinas concludes that “nothing necessary to faith is contained under the spiritual sense which is not elsewhere put forward by the Scripture in its literal sense.”
Thomas’ dependence on extra-Biblical philosophy
It is unfortunate, then, that Aquinas is not always consistent with his own methodology. At times he operates with a controlling hermeneutic not of the plain sense of scripture, but of ad extra philosophical constructs such as Divine Simplicity. Karen Kilby rightly observes that problems occur (or at least get worse) when Aquinas moves from a discussion of Biblical words like ‘Father’, ‘Son’ and ‘ Holy Spirit’ to a more abstract dimension of Trinitarian reflection.
I will focus on just one example of this: namely Thomas’ treatment of the Divine persons as ‘subsisting relations’. Kilby traces this idea first to Gregory of Nazianzus and then to Augustine. She goes on to contrast this with the so-called ‘social Trinitarian’ model of three ‘somethings’ united in love. Aquinas appears to be exclusively speaking of ‘relations without relata’, a thought which is unthinkable for the human imagination (and hence enters the realm of the apophatic). I think this assessment is accurate in regards to Aquinas, but that he has also mutated the tradition in a significant way.
Aquinas begins with the Boethian definition of person: ‘persona est rationalis naturae individua substantia.’ as a translation of the Greek hypostasis which Thomas further defines as ‘an individual in the genus of substance’. This does not suggest relations without remainder but rather indicates an individual existence for each hypostasis. However, in light of what we have argued earlier regarding Thomas’ doctrine of analogy defining terms univocally and then applying them in the ‘mode of supereminence’, Aquinas appears to apply the term ‘persons’ to God exclusively as ‘relations’(‘persona est relatio’),. He is attempting to strip the term of its empirical limitations, leaving only the perfection and not the finite mode of signification. McCabe comments:
“Aquinas quotes with ostensible approval Boethius’ definition of a person as ‘an individual substance of rational nature.’ But, as speedily emerges, the ‘persons’ of the Trinity are not individuals, not substances, not rational and do not have natures. What Aquinas labours to show is that in this unique case ‘person’ can mean relation.”
An investigation of the trajectory of ‘persons as relations’ within the tradition however reveals that Aquinas’ reductionist interpretation is a novelty.  Augustine, for example, who also deployed the language of relations could at the same time still link these to their relata. So in De Trinitate he writes:
“..every being that is called something by way of relationship is also something besides the relationship; thus a master is also a man, and a slave is a man…….If the Father is not also something with reference to himself, there is nothing there to be talked about with reference to something else.”
Commenting on the Augustinian understanding in contrast to that of Aquinas, Moltmann writes:
“…this relational understanding of the Persons has as its premise the ‘substantial’ interpretation of their individuality; the one does not replace the other.”
Similarly, it is significant that Gregory of Nyssa who defended the ‘relations’ idea is also one of the most explicit proponents of the ‘threeness’ of the Godhead to the extent that he had to defend himself from those who accused him of preaching three Gods. Likewise Basil speaks boldly (and by modern Barthian standards somewhat crudely) of Peter, Andrew and John united by the common predicate ‘man’ as an analogy of Father, Son and Spirit united in the one nature ‘God.’ This very clearly avoids modalism and is consistent with those theologians who speak of the persons in terms of three ‘centres of consciousness’, or three ‘Subjects’ and ‘centres of action’. Aquinas’ weakness is that his model precludes any such description.
A primary consideration for the shift to a reductionist interpretation of persons in terms of ‘relations’ seems to be for Aquinas his commitment to a strong form of Divine simplicity. This states not only that God, as an immaterial mind, is not composed of parts ( a weak form of Divine Simplicity), but also the strong claim that God is identical with all his properties and that in some ineffable way they all identical with one another, so that it would be more accurate to say apophatically that God does not have any properties. This doctrine is so fundamental for Aquinas that he deals with it as of first importance in Summa Theologiae 1a, Question 3. “since God is absolute form, or rather absolute being, He can be in no way composite.”
Although attractive for Christian apologetics in providing a possible solution to the Euthyphro dilemma and in strengthening the cosmological argument, this doctrine of God has the weakness of not being taught in the Scriptures themselves. It has been questioned in modern times not only by the radical Process theologians such as Hartshorne and Griffin, but also by more conservative scholars such as Moltmann, Ward, Pannenberg, and Plantinga.
It is not difficult to trace this doctrine back through the mystical tradition of Pseudo-Dionysius (c.500 AD.) to the neo-Platonist Plotinus (204-270AD) and beyond to the pre-Socratic Parmenides (c.515-440 BC). Indeed the whole mystical tradition could be seen as a ‘series of footnotes to Parmenides’ (to misquote A.N. Whitehead)! Parmenides poem ‘On Nature’ refers to the simplicity of The One in Fragment 8:
“Nor is it divisible, since it all alike is;
Nor is it somewhat more here, which would keep it from holding together,
Nor is it somewhat less, but it is all full of what is.”
Parmenides argues that the One must be indivisible, otherwise in one place it would be one thing and in another would not. Yet for Parmenides it is not possible to speak of what is not (being non-existent) and therefore reality must be one indivisible plenum.
Interestingly, Aquinas turns the premise of Parmenides on its head: God is wholly simple therefore we can only speak of what God is not and not what He is (univocally)! For Parmenides, on the other hand, it is impossible to speak of what is not therefore the One must be wholly simple (indivisible). In order to avoid the post-hoc fallacy then we must admit that Aquinas inherits Parmenides’ One only indirectly through Augustine and Pseudo-Dionysius.
Of course it would also be a genetic fallacy to conclude that the doctrine of simplicity in Aquinas must be false solely on the basis that we can explain its origin. What we do observe, however, is that Aquinas struggles to squeeze the doctrine of the Trinity into this alien mould of Parmenidean simplicity – which is really a radical Unity without distinctions, rather than submit this construct itself to the revealed ontology of the Tri-unity manifested in the ‘history of God’. In other words, we can only truly understand the immanent trinity by means of the economic trinity as revealed in Jesus Christ and the outpouring of the Spirit.
The traditional doctrine of the trinity, in contrast to the heresy of modalism, associated with Sabellius in the early third century AD, demands that there are real distinctions in God (and therefore real generation and real procession). Modalism teaches that ultimately God is only one person. In order to hold onto orthodoxy, Aquinas agrees in Summa Theologiae that “relations exist in God really.” and that:
“if the relations were not really distinguished from each other, there would be no real trinity in God, but only an ideal trinity, which is the error of Sabellius.”
The problem with Aquinas, is not in what he says, but in what he also says. Aquinas’ instinct, arising from the organising principle of Simplicity, leads him towards the very modalism he seeks to avoid, when he asserts, “it is manifest that relation really existing in God is really the same as His essence and only differs in its mode of intelligibility.”
Aquinas illustrates his position with Aristotle’s example of action, passion and motion to show that fatherhood and sonship are logically distinct in a similar way. This could be criticised however as pointing to the conclusion that God is one person (in the modern sense of the term) with logically distinct self-relations. In other words, this still leads to Sabellianism.
Cornelius Plantinga observes that, to avoid modalism, it is not enough for Aquinas simply to show that these relations are logically distinct, Aquinas must show that they are really distinct.
Instead, Thomas presents a position which appears to endorse two mutually incompatible beliefs: namely that subsisting relations really differ from each other and not only in our understanding but also that they differ only in our understanding. Karen Kilby observes the same dilemma in her essay.
Another problem not addressed by Thomas is how, within his model of the Trinity, the Son can know that he is the Son and distinct from the Father? and how the father can know that he is the Father and distinct from the Son when according to simplicity there is only one knowledge and one consciousness?
It is noteworthy that Aquinas’ contemporary Dominican, Meister Eckhart (1260–c. 1328) followed Divine Simplicity to its more consistent and logical conclusion, seeing in the concept of the Trinity a mere representation of the Father as knowledge, the Son as Life and the Holy Spirit as Being beneath which lies a Unity without distinction (‘unum non unus’). One of the articles for which he was condemned as a heretic by Pope John XXII was that:
“24. Every distinction is alien to God, both in his nature and in the persons. The proof: since His nature itself is one (una) and this very One (unum), and each Person is one and this same One as the nature.”
The principle of ‘Ockham’s Razor’), that ‘all things being equal, the simplest explanation is the best’, is named after another contemporary of Eckhart’s: the Franciscan, William of Ockham But Ockham’s Razor is itself is a logical fallacy. It led Ockham down a different, but analogous error to Eckhart by denying that properties or concepts exist except in name only. This ‘Nominalist’ school prefigures in many ways the later reductionism of Logical Positivism and scientism. In his award winning poem, ‘Snow’, poet Louis MacNiece challenges an oversimplification of reality.
“…World is crazier and more of it than we think. Incorrigibly plural.” 
A problem remains though. Is it possible to jettison Aquinas’ doctrine of Divine simplicity and still have an answer to the ‘Euthyphro dilemma’? How, can universals such as goodness, or the law of non-contradiction not be a standard higher than God without denying their existence? Augustine's solution, taken up by Aquinas, was to place universals in the mind of God. Here the universal ideas are not independent but remain eternal and a basis for the decisions of God’s will (and hence his decisions are not arbitrary). We can still affirm Augustine’s answer without taking the next step that all universals are identical and collapse ineffably into one within God. As an immaterial Being, God is simple in the weak sense of ‘not composed of parts’ in an analogous way to the human immaterial mind, yet He need not be simple in the strong sense argued by Aquinas as a necessary resolution of the Euthyphro dilemma or to reply to the atheist objection to the cosmological argument. ( that the universe is simpler than a complex God). Aquinas, at least for these purposes, proves too much. (I am not suggesting this was Aquinas’ purpose, but it may be a modern rationale for retaining his theology).
The result of Aquinas proving too much is an intractable set of difficulties for his doctrine of the Trinity which are highlighted in Karen Kilby’s article, and can only be accommodated within the apophaticism which she personally endorses. I have argued however in this paper that in at least three areas: namely his doctrine of analogy, belief in revelation and the plain sense of Scripture, Aquinas has made great strides to escape from the confines of the type of apophaticism taught by mystics like Plotinus or Pseudo-Dionysius. As a child of his time, however, he never completely succeeded. He did not work through the full implications of his insights regarding the controlling authority of the revealed words, because, to borrow a phrase from Wittgenstein, ‘a picture held him captive’: primarily the extra-Biblical ‘picture’ of absolute Divine Simplicity. This paper has argued that this picture is fundamentally at odds with the orthodox doctrine of the Trinity, being more consistent with Sabellianism, and lands Aquinas having to defend mutually incompatible views. The only way out for Aquinas it seems, is to take refuge, (unfortunately, in my view), within the fog of apophatic theology, with its claims that God is in essence unknowable.
 Karen Kilby, Aquinas, the Trinity and the Limits of Understanding, 2008 p.15
 Op cit p. 16
 Op cit p.18
 Op cit.
 Thomas Aquinas: Summa Theologiae, 1a, q. 3 prologue.
 Gregory Nazianzus, Second theological oration, in Edward R. Hardy (ed), Christology of the Later Fathers, (Philadelphia, Westminster Press 1954), p.136-159.
 I Timothy 6:16.
 1 Corinthinans 13:12, 9.
 Pseudo-Dionysius, On the Divine Names.
 Ibid chapter 2 Pseudo-Dionysius The Complete Works translated by Colm Luibheid, Paulist Press 1987 edition p. 61.
 Ibid, The Mystical Theology ch 1, p.136
 Aristotle, On interpretation 17a 31-33 cited in Colm Luibheid (above).
 Out of respect for Dionysius, Aquinas tries to reinterpret him, reading the affirmations as referring to the ‘meaning of the name’ and the denials as ‘the mode of signification.’ ( Summa Contra Gentiles Bk 1, ch 30, par 3.
 The point of Hegelian logic is to “make clear the inadequacy of the notions (which it) considers one by one and the necessity, in order to understand them, of raising each to a more complete notion which surpasses while integrating them.” Cited in Sartre, Being and Nothingness, (Routledge 2008), p.36
 Eg Peter Rollins: How (not) to speak about God. (SPCK 2006)
 Sartre, Being and Nothingness, (Routledge 2008), p.21
 Thomas Aquinas, Summa Theologiae 1, 9:3
 Aquinas, Summa Contra Gentiles, Bk 1, ch 7
 Aquinas, Summa Theologiae 1a, q. 3, art 7
 Aquinas, Summa Contra Gentiles, Bk 1, ch 32, par 3
 Summa Theologiae 1a 13.1-6 The Latin for ‘word’ here is nomina, also translated ‘names’ as in Pseudo-Dionysius’ book: ‘The Divine Names’, but Timothy McDermott believes that in both cases the word nomina has a wider connotation than just ‘names’, so uses the translation ‘words’. Timothy McDermott (transl) Aquinas: Selected Philosophical Writings (Oxford University Press 1993) p. 214
 In Thomas’ day the writings of Pseudo-Dionysius had become more widely available.
 Dionysius (Cel. Hier. ii)
 Thomas Aquinas, Summa Theologiae, 1a, 13, 12
 Keith Ward, God: A guide for the perplexed, Oneworld publications 2005.
 Herbert McCabe, Aquinas on the trinity, essay in Davies and Turner (ed), Silence and the Word, (2008)
 Aquinas, Summa Contra Gentiles, Bk 1, ch 32.
 Aquinas, Summa Contra Gentiles, Bk 1, ch 32, par. 3
 Aquinas adds, for example, the arguments that God is simple and has no accidents. (SCG Bk1, ch 32, par 3-5).
 Karl Barth was one of the few theologians to reject Aquinas’ solution, but he admitted that he had nothing to replace it with. Karl Barth, Church Dogmatics, vol 2, (Edinburgh T & T 1964), p. 230.
 Aquinas, Summa Contra Gentiles Bk 1, Ch 29, par 5.
 A.N.Williams, The Ground of union (Oxford University Press 1999). See also Aquinas, Summa Contra Gentiles, Bk 1, ch 29, par 6.
 Aquinas quotes Dionysius’ Celestial Hierarchy in Summa Theologiae 1, art 9. and On the Divine Names in Summa Contra Gentiles Bk 1, ch 29, par 4
 Norman Geisler, Thomas Aquinas: an evangelical appraisal (Baker 1991), ch 10, but see footnote 104.
 Ibid 1, 13, 6
 Ibid 1, 13, 5
 Ibid 1a, 13, 1
 Ibid 1a, 13, 12
 Ibid 1a, 13, 12
 This point can still be maintained if as I argue one holds to only a weak doctrine of simplicity.
 See discussion in Geisler, Thomas Aquinas: an evangelical appraisal (Baker 1991) ch 3 and ch 10
 Aquinas, Summa Contra Gentiles Bk 1, ch 30, par 2
 Summa Theologiae 1a q.13, 5.
 Ibid I, 12, 8
 Ibid I, 12, 7
 Ibid 1,13,9
 Ibid 1,13,9
 Ibid I, 12, 7
 This appears to be Anthony Kenny’s view in Aquinas (Oxford University Press 1980), p.9.
 Aquinas, Summa Contra Gentiles Bk 1, ch 30, par 4
 Roy A. Clouser, The Myth of Religious Neutrality(University of Notre Dame Press 2006), p.230
 Aquinas, Summa Contra Gentiles Bk 1, ch 5, par 6
 Aquinas, Summa Theologiae, 1. 12,5. I am indebted to this reference from A.N.Williams discussion in The Ground of union (Oxford University Press 1999) p.38
 Norman Geisler, Thomas Aquinas: An Evangelical Appraisal(Baker 1991) p. 43
 Thomas Aquinas, Summa Theologiae 1a 1,10
 Thomas Aquinas, Summa Theologiae 1a 1,10
 Nicholas M. Healy, Thomas Aquinas: Theologian of the Christian Life (Ashgate 2003) p. 47
 Thomas Aquinas, Summa Theologiae 1a 1, 1
 Ibid 1a 1,1
 Ibid 1a 1,6
 Ibid 1a, q. 42, art 7
 Ibid 1a, q. 32, art 1
 Ibid 1a, 1,10 ad 3
 Thomas Aquinas, Summa Theologiae 1a.1,8.
 Thomas Aquinas, Commentary on the Book of Job,13, lecture 1
 Plotinus, Enneads II, 4, 11
 Ibid V, 3, 13
 Ibid V, 5,6
 Ibid V, 5,4
 Thomas Aquinas, Summa Theologiae 1a 1,7
 Eg Luther, The Pagan Servitude of the Church: A first Inquiry p310,311 in Woolf, Reformation Writings of Martin Luther Vol 1. (Lutterworth Press 1952).
 Ibid p.312.
 Pseudo-Dionysius, The Celestial Hierarchy ch 2 140A, (ibid p.149)
 I am grateful to Joseph Vnuk for this reference which is taken from Aquinas. Summa Theologiae I. 108
 Thomas Aquinas, Summa Contra Gentiles Bk1, ch. 4, 1-3.
 Eg John Wycliff: “We will give God’s Word to God’s people and God’s Spirit will teach them”. So Luther aware of the pseudepigraphy of Dionysius can regard him as “more of a Platonist than a Christian” and advise his readers “(not) to give the least weight to these books.” (which were a favourite of his nemesis John Eck)!
 Karen Kilby, Aquinas, the Trinity and the Limits of Understanding, 2008 p.22-23
 Eg by apophatic writer Peter Rollins, in How (not) to speak about God, (SPCK 2006)
 Thomas Aquinas, Summa Theologiae I, 1,10.
 Ibid. I. 66 ar.1
 “That signification whereby things signified by words have themselves also a signification is called the spiritual sense, which is based on the literal, and presupposes it”. (ibid 1,1,10)
 Ibid Ia, 1,10
 Ibid 1a,1,10
 Aquinas, Summa Theologiae, 1, q.40, a.2
 Aquinas, Summa Theologiae, 1, q.40, a.2
 Herbert McCabe, Aquinas on the Trinity in Oliver Davies and Denys Turner (ed), Sllence and the Word: Negative Theology and Incarnation, (Cambridge 2008) p. 92
 Barth takes Aquinas’ definition (together with his assumption of Divine simplicity) as a springboard for dispensing of the term ‘person’ altogether since it might carry an unacceptable (for Barth) connotation of ‘a centre of consciousness’. He replaces it with his preferred term ‘mode of being’. Karl Barth, Church Dogmatics 1:1, (T&T Clark International), 2004
 And this is in spite of the fact that Augustine also held (inconsistently in my view) to a strong view of Divine Simplicity.
 Augustine, De Trinitate, VII, 2 (219-220).
 Jurgen Moltmann, The Trinity and the Kingdom of God, (SCM 1981), p. 172
 Gregory of Nyssa, An answer to Ablabius: That we should not think of saying that there are three Gods. In Hardy, Christology of the Later Fathers (Westminster Press 1954)
 Basil, Letter 38, par 2
 Augustine rejected this illustration, though it can be defended imperfectly and by analogy. God is not in a genus, as Aquinas recognised. God is the category in which we all participate contingently and which we understand analogically.
Scott, Howard, J. ‘Toward a Biblical Model of the social trinity: avoiding equivocation of nature and order’, (Journal of the Evangelical Theological Society, Sep 2004)
 Eg W.Pannenberg, Systematic Theology, T&T Clark Ltd 1991, p.319
 ST, 1a, q.3, art 7
 Eg Charles Hartshorne, The Logic of Perfection (Illinois 1962).
 David Ray Griffin, God, power, and evil: a process theodicy, (Westminster John Knox Press, 2004)
 Eg Jurgen Moltmann, The Trinity and the Kingdom of God, (SCM 1981),
 Keith Ward, Rational Theology and the Creativity of God, (Blackwell 1982), ch 3-4.
 W.Pannenberg, Systematic Theology, T&T Clark Ltd 1991,
 Alvin Plantinga, Does God have a nature? (Marquette University Press, Milwaukee 1980).
 Parmenides of Elea, Fragments: A Text and translation with an introduction by David Gallop, (University of Toronto Press 1984), Fragment 8 lines 22-25.
 The ‘history of God’ is a Moltmannian term. (also used by Pannenberg who interprets theology through the lens of history).
 ST, 1, q.28, art1
 ST, 1, q.28, art 3
 ST, 1, q. 28, art 2 italics mine.
 ibid p. 41 quoting Summa 1a, q.28, art 3, ad 1
 Cornelius Plantinga Jr. in Feenstra and Plantinga (ed), Trinity, Incarnation and Atonement, (University of Notre Dame Press 1989). p.41
 Karen Kilby, op cit.
 M.O’C.Walshe (ed and translator), Meister Eckhart: Sermons&Treatises Volume 1 (Element Books 1979). P. xxxiv
 Ibid p.l(It could be countered in Eckhart’s defence that Pope John XX11 was also a heretic in condemning the poverty of Francis, but this would be an ad hominem argument! Eckhart’s view really is heresy because it departs from the orthodox formulation of the Trinity and not just because this particular pope said it did).
 Louis Macniece, ‘Snow’
 Eg Richard Dawkins, The God Delusion.
 It may also be incompatible with his doctrine of analogy if we take Geisler’s interpretation of it as based on univocality of definitions. According to Summa Contra Gentiles Bk 1, ch 32, par 4 even definitions cannot be predicated of God univocally because there are no accidents in God as a result of Divine simplicity. Geisler’s theory could be salvaged however if we take Aquinas to mean merely that the definitions are applied differently. (an interpretation supported by SCG Bk 1, ch 34 par 5).