1. IntroductionFootnote 1
In the second question of the Summa Theologiae, St. Thomas Aquinas gives five demonstrations for God's existence. The ‘five ways’, as they are commonly known, have provoked intense debate and acquired a great deal of prominence in Thomistic scholarship. This essay reconsiders the place of the ‘five ways’ in Thomas’ thought. Frequently, the proofs are interpreted as indicating that faith and philosophy seek the same thing, and that one can refer to God by natural reason in the same way as one does in faith. Yet as I will argue here, the proper relation between faith and natural reason only comes into view in light of Thomas’ claim that the proofs only refer deficiently, or improperly, to God. The five ways do help us to understand the relation between faith and natural reason, but they do so only when they are read in the context of the first part of the Summa. When read in this context, the five ways become an apophatic moment within Thomas’ Dionysian understanding of an eminent naming of God. Through sacred doctrine, the eminent discourse of faith allows one to name God properly, ordering and perfecting natural reason's deficient naming of God. Thomas demonstrates the perfection of naming by taking up the five ways into the ‘five notions’ of the Trinity (I.32.1), absorbing the proofs’ content while transforming their mode of signification.
The work of Saul Kripke, the influential theorist of reference, can help us to understand how Thomas distinguishes the discourses of faith and natural reason in terms of their modes of signification. Kripke's work distinguishes between necessary and contingent reference, and sees proper names as having necessary reference, while descriptions only refer contingently. For Kripke, a proper name designates the same object in all possible worlds. By referring singularly to a particular object, a proper name designates its object necessarily, even if this necessity can only be known a posteriori. On the other hand, descriptions are only contingently related to the object that they describe, even though they may be known a priori. For example, if someone says, ‘Willie is the guy in the grey suit,’ they would be referring to me. If you check back in five years, I will still be ‘Willie’– the proper name will still designate me. However, in five years, the description ‘the guy in the grey suit,’ like the grey suit itself, will no longer fit. Even if your knowledge that I am wearing a grey suit helps you to identify me today – in Kripke's terminology, fixing the reference – this description only applies contingently.Footnote 2 In five years, someone else might wear a grey suit. Since the description does not refer to me in all possible worlds, its metaphysical status is contingent.Footnote 3 However, since a name (‘Willie’) will identify its referent in all possible worlds, in modal terms the proper name identifies its object necessarily.
Kripke makes this distinction between necessary and contingent reference in the context of a discussion of singular reference. We often assume that we can refer to something because we can describe it. Kripke's work reverses this; on his view, it is because we can refer to something ostensively that we are able to describe it. As Kripke writes, ‘Once we realize that the description used to fix the reference of a name is not synonymous with it, then the description theory can be regarded as presupposing the notion of naming or reference.’Footnote 4
Kripke's work is useful in understanding Thomas because the ‘five ways’describe God's activity towards the world, but do not refer singularly to God as a unique being. Only through sacred doctrine – in which God is properly named – does singular reference to God become possible. The ‘five ways’ fix the reference of our language about divinity, but they are not synonymous with names of God. Where the five ways describe God's activity, Thomas’ doctrine of the Trinity names God, and thus refers to God singularly. It is in the light of faith, and the understanding of the Trinity, that we come to understand (or believe) how natural reason's knowledge applies to God. To flesh out this claim, let us turn to the Summa.
2. ‘Naming’ God by Natural Reason
Question 2 of the Summa Theologiae gives a brief summary of how natural reason fits into sacred doctrine. Its incorporation is significant: not only for the doctrine of God, but also for the appropriation of Aristotle's Ethics(in the prima and secunda secundae) and the development of Christ's Incarnation. In the first article, Thomas asks whether God's existence is self-evident for us. He answers that it is not, in the process rejecting the ontological argument.Footnote 5 The ontological argument is rejected because we cannot know God's essence. While God's essence is to exist, so that God's existence is self-evident to God, we do not know God's essence, so God's existence cannot be self-evident to us. We cannot know a priori that God exists. Thomas argues, however, that we can know God by God's effects; this knowledge by effects then takes the form of the five ways.
Thomas makes an intriguing statement in responding to the first objection of article one. Often overshadowed by the second reply's more famous rejection of the ontological argument, the first reply makes the following statement: ‘To know that God exists in a general and confused way is implanted in us by nature … This, however, is not to know absolutely that God exists; just as to know that someone is approaching is not the same as to know that Peter is approaching, even though it is Peter who is approaching’(I.2.1 ad 1). As Thomas says here, natural reason's knowledge of God is only a general or confused idea of God. This ‘someone’ that we know by natural reason is what Thomas would call a ‘vague individual.’ A ‘vague individual’ signifies a determinate nature or activity without signifying a determinate individual of that nature.Footnote 6 To know that someone is coming allows one to describe her, but not properly name or singularly refer to her. In the case of the proofs, if other things might fit these descriptions, then each of the five ways only contingently identifies God. In short, natural reason does not make possible singular reference to God because it imprecisely signifies God's singularity and individuality, only vaguely understanding that ‘someone’ is there.
A brief summary of the five ways will help to show how they deficiently signify God. As Anthony Kenny notes in his study of the five ways, they parallel the modes of causality that are found in the world.Footnote 7 We know God by God's effects in the world, treating the modes of causality of the world as effects, and reasoning to the existence of their cause. A demonstration from effect to cause (a quia demonstration) cannot tell us what the cause is of itself; it is therefore a deficient form of knowledge. Indeed, in knowledge by effects, we substitute the effect for the definition (i.e., for the essence of the thing). It lets us know a cause is there, but not what the cause essentially is. The five ways, which proceed from our knowledge of worldly causality to a divine cause, are quia demonstrations.Footnote 8 Moreover, because we deduce the existence of the cause as a condition for the possibility of the world, one can argue that the five ways are a priori demonstrations.Footnote 9 As a priori demonstrations, which may apply to God but do not necessarily do so, we will see that the five ways are best understood as descriptions. Naming neither God's determinate essence nor the determinate individual who is God, the five ways only vaguely or contingently refer.
Let us turn to the five ways themselves, to see how they are descriptions. The first way is the argument from motion or change. Some things in the world are in motion, or more broadly considered are undergoing change. For Thomas, the change of something from being at rest to being in motion is a change in its nature from potential to actuality, and this is only possible if something that is already active sets the potential mover in motion. Without positing an unmoved mover, the world's motion and change would remain inexplicable. Therefore, by a per impossibile syllogism, we are rationally justified in positing a prime mover, moved by no other, which all people call God (omnes intelligunt Deum)(ST I.2.3).Footnote 10
The arguments of the second and third ways are structurally similar to the first way, but with respect to efficient causality and the possibility and necessity of things in the world. The ‘prime mover’ shows that we must think of something that is unmoved (primum movens, quod a nullo movetur), while the first efficient cause conceives of something that activates itself. Likewise, the third way's ‘necessarily existing being’ is a being that exists through its own activity (and thus, whose essence is to exist). All three arguments share the following logic: things in the world cannot move others, act as causes, or exist of themselves. Without positing things that possesses these qualities, however, we cannot rationally account for the origin of mediate causality or the existence of things we see in the world. From these effects that we encounter in the world, we can deduce the existence of their cause; we can argue for the existence of a prime mover, first cause, and necessary being, even though we only know these causes imperfectly through their effects. By substituting these effects for God's unknown essence in our definition of God, all people can name (nominant) the posited prime mover, first cause, or necessary being ‘God.’ However, such ‘naming’ substitutes the demonstration for the essence, and thus does not really name God properly, as shall be explained further below.
Matters become more complicated when we turn to the fourth and fifth ways of demonstrating God's existence. As Victor Preller has noted, the fourth and fifth ways share little with the first three ways, and may even be opposed to them.Footnote 11 The fourth way argues for a most real being in which existence, goodness, and truth are unified most eminently. The goodness, truth and existence we see in the world are cases of a general class of types of goodness, truth, and existence. As cases of a general class, they cannot themselves be that which defines the class. There must be something else in which truth, goodness, and existence exist in the highest way so as to cause these qualities in things in the world, and this ens realissimum we call God.
The fifth way argues for God's existence based on the order we see in the world. Seeing that things tend naturally towards their end, Thomas argues that there must be something that moves them towards that end, especially in the case of nonsentient beings that cannot move themselves. The regularity of the world, rather than its directedness towards a particular end, is thus the basis for calling the governor of the world ‘God.’ From the tendency of things in the world to fulfil their own natural ends with regularity, we can conclude that there is order; we cannot, however, thereby reason to the goal of the universe as a whole.
To summarize, from what Aquinas knew of causality in the world, one can reason to the existence of a prime mover. One can also reason that there is a first efficient cause, and a being that is necessary of itself. In addition, there is a ‘maximal’ being (ens realissimum) and something that governs the world. All of these are called God, but do they refer singularly to God? If we read the five ways as referring to God, problems begin to arise. First of all, while the same being could be several of these at once, these different activities are only contingently related to one another. The prime mover need not be the most real being, nor need the first efficient cause be the governor of the world. In other words, there is no principle internal to the five ways that unifies these ways of naming God.
More importantly for Thomas, the five ways only reason to a being who exists in conjunction with the world. The fifth way may provide the clearest case of the problem. To treat God as the fifth way's ‘governor of things’(gubernator rerum) equates God's providence with the final causality of natural teleology. Thomas would clearly not want to do this, as it belies his claim that we cannot know by natural reason the providential end towards which creation is directed (I.1.1). In all five ways, one is describing God's activity as belonging to the same genus as the activity of the world; one thereby subsumes God's activity under a genus. Since it is opposed to worldly causality, the causality of the five ways remains within the same genus as the causality of the world, even if the five ways are not, strictly speaking, the same as the observed causality of things in the world. To take the five ways as referring to God therefore creates a massive tension: such generic description of God's activity is incompatible with Thomas’ claims that God is neither a member of a genus nor of a species (I.3.5). In short, the five ways do not do justice to the theological claim that God is unique, nor the claim that God creates the world freely and directs it towards a final, supernatural end. In light of Thomas’ theological commitments, to read the five ways as naming God becomes highly problematic.
These problems with the five ways are important because they arise when one relates the five ways to central doctrinal tenets held by Thomas elsewhere in the Summa. The Summa is an exercise in reflection on sacred doctrine; to assume that the five ways properly name God would render the Summa internally inconsistent. Therefore, in order to understand the place of the five ways in the Summa, they should be read as descriptions in the Kripkean sense. The five ways are contingent demonstrations of God's existence based upon things that we discover in the world. When Thomas says that natural reason can know that ‘someone’ is God, as a general and confused idea, he is affirming our ability to describe God from God's effects. This description, however, remains a deficient or contingent mode of reference, in which anything that fits the bill could be substituted for God. For example, as Anthony Kenny notes, the prime mover of the first way need not be outside the world; a self-moving world could serve just as well.Footnote 12
The five ways, then, give us a general idea of what God is without telling us who God is, functioning much like a personal advertisement. If I put a personal ad in the paper, seeking a brown-haired woman, one with a nice personality, one with a sense of humor, who likes swing dancing and playing golf, I might get my wife. Or five different women might respond, and these five qualities would tell me nothing at all about who they are, in terms of their character. I would not know their essences, so to speak. The five ways function similarly, like the following personal ad:
Medieval Monastic Philosopher is seeking a prime mover, first efficient cause, a being necessary of itself, and most real being. Governance of the world required. Solution to problem of evil a plus. I like demonstrations from first principles, contemplation, and Platonic dialogues. I know you’re out there – let's get together!
Like a personal advertisement, the five ways are descriptions: we can know them before encountering God, or knowing God's name, so that they are a priori. Yet, in that something else might fit the description as well as God, they remain contingent. As a priori, contingent descriptions, then, the five ways tell us that there is a ‘God,’ but they do not permit scientific knowledge of God (scientia dei). In fact, since what we ‘know’ of God via the five ways is really just a negation of what we know via the causality of the world, the five ways confirm Thomas’ dictum: we can only know God by saying what God is not.Footnote 13
In summary, the five ways do not refer to God as God, since they fail to name God as unique, singular, or simple. This is important, because the five ways are often read as either rationally justifying Christian belief, or as leading to a flawed natural theology. However, reading them as descriptions of God, based on God's effects, offers a more appropriate middle route between these two alternatives. As descriptions, they may apply to God, but we cannot know how they apply until we discover who God is. For Thomas, we discover this in faith; only then do we discover how the description fits. Precisely because we can name rather than describe God in faith, faith orders, perfects, and redirects the vague and confused idea of God acquired through natural reason.
3. Naming God in Faith
A significant difference between natural reason and faith for Thomas is the difference between their modes of signification, which effectively enable two different relations to God. As Victor Preller writes, ‘The id a quo of ‘God’ as that term is used in natural theology has such a radically different modus significandi from the id a quo of ‘God’ as that term is used in dogmatic theology, that the two could not be explicated in terms of the same conceptual framework or logical space.’Footnote 14 Specifically, natural reason does not grasp the personal dimension of God, or God's individuation. Because natural reason only grasps a vague conception of God's activity, it cannot necessarily refer to God, because it lacks the determinate signification for this one, singular being. As Kripke argues in his discussion of reference, stipulating a particular object is a necessary condition for the transworld identification that enables reference. As he writes, ‘Possible worlds are stipulated, not discovered by powerful telescopes. There is no reason why we cannot stipulate that, in talking about what would have happened to Nixon in a certain counterfactual situation, we are talking about what would have happened to him.’Footnote 15 When Thomas says that faith lets us know ‘more’ about God than natural reason, one of the additions to our knowledge is its personalization of divinity, which lets us stipulate that we are talking about a particular, unique being. As he writes, ‘we know God more fully … according as we attribute to Him some things known by divine revelation, to which natural reason cannot reach, as, for instance, that God is Three and One’(I.12.13).
The deficiency of the demonstrations is most evident when one considers Thomas’ remarks on the most proper names for God. ‘God’ is not the most proper name for us to use for God, since it signifies the divine nature (I.13.8), without individuation. More proper is the name ‘He (The one) who is’(Qui est), which signifies God's self-subsistence and individuation: God is the one whose essence is to exist. The most proper name, however, is the Tetragrammaton, because it signifies both God's nature and God's existence: it is ‘imposed to signify the substance of God itself, incommunicable and, if one may so speak, singular’(I.13.11). Thus, while people ‘name God’ from the five ways, such naming remains imperfect, unable to signify a determinate individual.
To say that the five ways do not signify a determinate individual is to say that they lack the mode of signification known as a suppositum. Thomas argues that the mode of signification proper to naming God is a mode of signification known as suppositum.Footnote 16 A suppositum is an individual that inheres in a nature. For example, Socrates was a suppositum of human nature, since human nature was concretely instantiated in the person of Socrates. As a mode of signification, suppositum is closely connected with the singular reference that we associate with proper names: a suppositum signifies something singularly as ‘this one.’ When speaking of God, however, we are speaking of a being individualized of itself and by its own activity; as Thomas says in I.3, God's nature is God's suppositum. Since God is self-individualizing, we cannot know God's nature, because God is an individual through and through. By signifying God as a suppositum, as ‘this one’ whose essence is to exist, we thus signify that we know God as one unknown. Thus, as with the Tetragrammaton, God's nature and individuality should go hand in hand, but the five ways do not adequately signify God's existence.
Because we generally know supposita through our senses, we associate their modes of existence and signification with materiality. For Thomas, we know something by abstracting the universal nature from the individual suppositum that we encounter through our senses. For example, Socrates is a suppositum of human nature by this body that he has. Such an association with materiality is clearly inappropriate for thinking or speaking about God, so such names still signify God deficiently. Only by negating the materiality thereby signified can this mode of signification be proper to God; such ‘concrete’(existent) terms must therefore be predicated metaphorically of God, since they apply primarily to creatures and secondarily to God (I.13.6).
In recognizing that the five ways lack concreteness, the specific way that they enable knowledge of God can be clarified. The five ways are the ‘intelligible conceptions’ of God that we abstract from sensible objects (I.12.13). They let us know of God ‘what belongs to God as the first cause of all things, exceeding all things caused by Him’(I.12.12). They also let us know that God differs from creatures, as the limitations of finite causality are removed from God; ‘not … by reason of any defect on His part, but because He superexceeds them all.’ As the abstract conception of God's divinity, the proofs signify God's activity, but do not signify the determinate agent who is the unmoved mover, necessarily existent being, or governor of all things.
In an interesting way, then, Thomas’ ordering of the modes of signification for naming God closely parallels Pseudo-Dionysius's account of the divine names.Footnote 17 We must name God concretely, given God's self-subsistence; however, the materiality of such names must then be negated. Then, moving toward God, one affirmatively predicates abstract qualities of God – being, life, good, etc. Given that the abstractness of these qualities as we conceive of them in worldly things is inadequate to their essential subsistence in God, we must then negate our understanding of these abstract qualities. Neither mode of signification, in itself, is adequate for naming God; rather, it is by passing through both, and denying the limits of each, that one moves toward a ‘sureminent’ naming of God.Footnote 18
While Thomas’ ordering of these different modes of signification suggests a correlation with Pseudo-Dionysius, questions 12 and 13 do not, of themselves, indicate how the demonstrations of God's existence fit into the discourse of faith. However, the discussion of divine names does suggest that the discourse of faith could take up such abstract conceptions, and draw one toward a more intimate knowledge of God by personalizing them. This change – brought about by integrating the five ways with a concrete mode of signification – occurs in Thomas’ doctrine of the Trinity, where the notions that articulate the internal life of the Trinity draw upon the five ways’ language of God's activity toward us.
4. The Five Ways and the Five Notions of the Trinity
As mentioned above, ‘proper naming,’ according to Thomas, involves signifying a determinate nature and a determinate individual. The five notions, like the Tetragrammaton, are effects known to us through scripture. Where the five ways only vaguely signify an individual, the doctrine of the Trinity signifies God's individuation, as three persons of one nature. A person is, as Thomas notes, a ‘suppositum of a rational nature’(I.29.2). To say that God is three persons, then, applies a concrete mode of subsistence to God's nature. In the activity of the five notions, these three persons of the Trinity are distinguished in their uniqueness and singularity, but it is the language of activity drawn from the five ways that lets us distinguish them. By closely examining the five notions in I.32.3, we can see the theological reason for the five ways of demonstrating God's existence by natural reason, a reason internal to the Summa's theological architecture.Footnote 19
In I.32, Thomas explains that there are five notions that constitute the relations between the persons, and thus their identities. He defines them as follows:
I answer that a notion is the proper idea whereby we know a divine Person. Now the divine persons are multiplied by reason of their origin: and origin includes the idea of someone from whom another comes, and of someone that comes from another, and by these two modes a person can be known. Therefore the Person of the Father cannot be known by the fact that He is from another; but by the fact that He is from no one; and thus the notion that belongs to Him is called ‘innascibility.’ As the source of another, He can be known in two ways, because as the Son is from Him, the Father is known by the notion of ‘paternity’; and as the Holy Ghost is from Him, He is known by the notion of ‘common spiration.’ The Son can be known as begotten by another, and thus He is known by ‘filiation’; and also by another person proceeding from Him, the Holy Ghost, and thus He is known in the same way as the Father is known, by ‘common spiration.’ The Holy Ghost can be known by the fact that He is from another, or from others; thus He is known by ‘procession’; but not by the fact that another is from Him, as no divine person proceeds from Him.
Therefore, there are Five notions in God: ‘innascibility,’‘paternity,’‘filiation,’‘common spiration’ and ‘procession.’ Of these only four are relations, for ‘innascibility’ is not a relation, except by reduction, as will appear later (I.33.4 ad 3). Only four are properties. For ‘common spiration’ is not a property; because it belongs to two persons. Three are personal notions – i.e. constituting persons, ‘paternity,’‘filiation,’ and ‘procession.’‘Common spiration’ and ‘innascibility’ are called notions of Persons, but not personal notions, as we shall explain further on
(I.40.1 ad a).The ordering of natural reason by faith becomes clearest when one considers how the five notions of the Trinity take up the language of the five ways while surpassing their mode of signification. The first notion, innascibility, is applied properly to the unborn (ingenitus; I.33.4) Father. The Father is, according to Thomas, the unbegotten begetter; while the Father is the source of the movement of the Son and the Holy Spirit, the Father is unmoved. Thomas's description of innascibility as ‘that the Person of the Father is from no one’(quod a nullo est), closely parallels the first way of a prime mover of the world (a nullo movetur). By naming the Father as innascible, one signifies singularly that this one is an unmoved mover.
The second notion, paternity, applies to the Father as one of the opposed relations that distinguishes the Father from the Son. The Father is distinguished from the Son as begetter from begotten. In his discussion of efficient causality (I.46), Thomas directly compares efficient causality to the begetting of a child. As efficient causality has to do with the setting-in-motion of an effect, a first efficient cause sets itself in motion. In the begetting of the Son by the Father in the Triune life, where they are distinguished by relation while sharing the same substance, both efficient cause and effect (Father and Son) are identical.Footnote 20 The relation of paternity in the Triune Life is therefore the primary analogate of efficient causality (the second way). For Thomas, all efficient causality in the world participates analogically in the divine life, following Ephesians 3:14: ‘I bend my knee to the Father of my Lord Jesus Christ, from whom all paternity in heaven and on earth is named’(I.33.2 ad 4). In naming God as Father, we can properly name God singularly in a way that transcends the vague signification of ‘first efficient cause.’
Filiation, the third notion, applies to the Son. Whereas the Father, as primary analogate of efficient causality, is the one who sets in motion the processions of Son and Spirit, the Son as begotten is the one so moved. As the one whose potential is reduced to actuality by the Father, the Son's existence is brought about by one of the same substance. The Son's existence, then, is necessary of itself, since Father and Son are only distinguished by their relation. Moreover, the revealing of the Name to Moses prefigured the Incarnation as the delivery of the human race (I.39.8). Thomas therefore appropriates to the Son its meaning of necessary or absolute existence. The Son, as a being necessary of itself, thereby fulfils the first part of the third way's demonstration. The third way further requires that possible things in the world receive their being from this necessarily existent being. This is appropriate to the Son as well, since the Son as Word implies God's intention to create – as Thomas says, in knowing God's self in the Word, ‘God knows every creature’(I.34.3). Through the Son's actuality, things in the world can come to be.
The fourth and fifth notions, common spiration and procession, apply to the Holy Spirit, personalizing the demonstrations of a most real being and a governor of the world. Common spiration, as the unity of the Father and Son, is the unity of truth, goodness, and existence in divine simplicity. As internal to the Trinity, common spiration signifies a unity of the transcendentals unique to the divine life. Whereas the ens realissimum of the fourth way can only demonstrate a generic notion of goodness univocal with truth and goodness in the world, common spiration permits us to signify primarily God's goodness in a nongeneric manner appropriate to God's simplicity and uniqueness. Goodness, being, and the truth of things in the world can participate analogically therein, without thereby determining the primary analogate or effacing its singularity.
The fifth way, the governance of the world, parallels the Spirit's procession as a procession of God's will. The Spirit, properly named as love or gift, indicates that God's will to govern in an orderly fashion and lovingly direct things to their end is internal to God's own self and characteristic of God's activity. The fifth notion tells us that the world is directed towards the celebration of the triune life. As Thomas writes in the Summa Contra Gentiles, ‘If, then, drive and motion belong to the Holy Spirit by reason of love, the government and propagation of things is fittingly attributed to the Holy Spirit.’Footnote 21 Through sacred doctrine, and the notion of the Spirit as gift or love, the end for which we were created becomes manifest to us (I.1.1).
The parallel between the five notions and the five ways, while interesting in its own right, takes on deeper significance in light of Thomas’ appropriation of a Pseudo-Dionysian approach to naming God. In light of the five notions of the Trinity, we can see why Thomas placed such importance on the five ways as telling us what God was not. They are abstract conceptions of God's activity that remove it from the sensibility and limitation constitutive of worldly causality. The eminent or mystical discourse, as represented in the notions of the Trinity, demands both preceding moments, but also orders them properly and frees them from their finitude even as it remains irreducible to either cataphatic or apophatic discourse. In this light, we reach the surprising conclusion that the five ways do not confirm Thomas’ status as a natural theologian. Rather, they are an apophatic moment in his mystical discourse on the Trinity, consistent with his account of divine names in I.13 rather than a strange aberration from it.
Two important clarifications need to be added. First, Thomas is quite clear that the five notions of the Trinity cannot be known by natural reason (I.32.1). The notions are believed in faith. Thus, the ordering of natural reason by faith moves from the top down – faith determines natural reason, and not vice versa. Second, even though the notions parallel the five ways, one should not equate the notions with the actions of the five. God's actions ad extra are unified actions of the Trinity. Thomas would not argue, and does not argue, that each of the five ways is the activity of one divine person.
To avoid this risk, one should recognize that the five notions, in effect, appropriate the activity of the five ways to the divine persons, without thereby dividing God's activity toward the world among the persons.Footnote 22 By naming God as triune, Thomas can affirm that it is characteristic of God to act in each of the five ways that we encounter through natural reason. God acts in these ways in God's self; the different types of causality represented in the five ways find their primary analogates in the internal life of the Trinity. In naming God as triune, Thomas states how God loves in freedom and acts simply even in apparently diverse and complex actions towards the world. Much as the different types of causality are not separate events, but rather consider the same event under different aspects, the five ways consider God's simple activity under the various aspects available to us by natural reason (I.13.4). The light of faith then transforms the vague and errant discourse of natural reason into proper, singular reference to God.
The assumption of the language of the five ways into Thomas's doctrine of the Trinity is thus an illuminating example of how faith perfects and orders natural reason. The language of the five ways is the material element of this doctrine, informed by the light of faith. Natural reason thus plays a crucial role in faith, albeit a subordinate and apophatic one. The language of natural reason is the only one we have, and only if it is assumed by faith can Christianity legitimately argue that human nature is redeemed. Given Thomas’ view that humans have a discursive understanding, the language of the five ways is quite important; without incorporating this discursive knowledge (cognoscere, not scientia), faith would not be able to give assent to sacred doctrine. In short, the language of the five ways, while inadequate in itself, provides sacred doctrine with a way of expressing God's triune love that humanity can grasp. It provides a language that lets us have some cognition of the relations of the Trinity, and thereby be drawn toward a more intimate, if still incomplete, knowledge of God.
In this light, the apparently esoteric, technical parallel between the demonstrations and the notions becomes highly significant, embodying the movement of the rational creature toward friendship with God. Without such assent, the ‘way of the rational creature to God,’ described in the secunda pars and tertia pars of the Summa, could not get off the ground; humanity could not act toward its final end, since the ‘vague and confused’ knowledge of God is also a vague and confused cognition of beatitude. By naming God as this unique one, through the personal signification found in the five notions, the intellect can voluntarily assent with certainty to the articles of faith (II–II.2.1). The incorporation of the discourse of natural reason makes faith a voluntary human action. It is through such voluntary assent that charity becomes a habit in the soul (II–II.23.2), making us ‘no longer servants … but friends’(John 15:15; ST II–II.23.1).
Thus, in light of Kripke's depiction of how we refer, we can better understand the role the five ways of demonstrating God's existence play in the Summa Theologiae. Only giving us a vague idea of who God is, they may refer contingently, but are best understood as descriptions. When taken up in faith, such that their mode of signification is transformed, they become part of the eminent naming of God as Triune, and as Father, Son, and Spirit, which refers singularly to God. By seeing both how the knowledge of natural reason is limited, and how faith reshapes it, the place of the five ways in the Summa thus illustrates the fundamental tenet of Thomas’ theology that grace perfects nature, rather than destroying it.
