¹ Kaufman, Gordon D., In Face of Mystery: A Constructive Theology (Cambridge, MA: Harvard University Press, 1993), p. 61Google Scholar.

² Ibid., p. 60.

³ Daniélou, Jean, God and the Ways of Knowing, trans. Roberts, Walter (Cleveland, Ohio: World Publishing Company, 1957), p. 89Google Scholar.

⁴ Wright, John H. S.J., ‘The Eternal Plan of Divine Providence’, Theological Studies 27, no. 1 (1966), p. 29 n. 4CrossRefGoogle Scholar.

⁵ To comprehend something is to know it fully or to know it to the full extent that it is knowable.

⁶ Indeed, in some cases, without such a revelation we can merely hypothesize about the existence of a particular reality (e.g. the existence of other intelligent life in the universe).

⁷ Rahner, Karl, Foundations of Christian Faith: An Introduction to the Idea of Christianity, trans. Dych, William V. (New York: Crossroad, 1984), p. 128Google Scholar.

⁸ See Aquinas, S.T. I q. 12 a. 7 corp.

⁹ Aquinas, Expositio in Librum De Causis, lect 6, n. 68. All translations of Aquinas are mine.

¹⁰ Ibid.

¹¹ Clarke, W. Norris S.J., The Philosophical Approach to God: A New Thomistic Perspective, 2^nd rev. ed. (New York: Fordham University Press, 2007) p. 63CrossRefGoogle Scholar.

¹² See Clarke, W. Norris S.J., ‘The Limitation of Act by Potency in St. Thomas: Aristotelianism or Neoplatonism?’, in Clarke, W. Norris S.J., Explorations in Metaphysics: Being—God—Person (Notre Dame, Ind.: University of Notre Dame Press, 1994), pp. 65–88Google Scholar and ‘The Meaning of Participation in St. Thomas’, in ibid., pp. 89–101.

¹³ See Aquinas Summa contra Gentiles, III., 113, De Potentia, q. 2 art. 1., Scriptum super Libros Sententiarum, Bk. I, dist. 4, q. 1, a. 1; Summa Theologiae I. q. 19 a. 2.

¹⁴ It might be better here to refer to efficient causality as quasi-efficient causality to highlight the difference between inner worldly efficient causality and the efficient causality of God's creative activity. This would allow us to insist both that God's efficient causality in terms of God's creative activity is an absolute beginning (“creation ex nihilo”) and to emphasize that the effect (i.e. creation) is distinct from God but not separate from God such that creatures are distinct limited participations in God as the infinite act of existence. Although Aquinas does not use this term, his participation metaphysics would support its use.

¹⁵ In creation God gives a gift (albeit creatures exist as distinct limited participations in the Infinite Act of Existence) and in grace God gives God's self. In speaking here of God as the ultimate causal source of all the perfections we find in the world, we are not simply speaking of God bringing things into existence (creation), sustaining them into existence (conservation), and moving them to act according to their natures (divine governance), but also the effects of God giving God's self to created persons, which would fall within God's governance. These effects are the fruits of the spirit. The created effect in human beings of God's self-communication (uncreated grace) is what is known as created grace. In Rahner's thought the self-communication of God in quasi-formal causality is uncreated grace or the indwelling of the economic trinity and it is the primordial grace that creates as its effect and as the condition of its possibility created grace, which is a created determination of the subject and is the disposition for union with God (i.e. sanctifying grace). See Rahner, Karl, ‘Some Implications of the Scholastic Concept of Uncreated Grace,’ in Theological Investigations I: God, Christ, Mary and Grace, trans. Ernst, Cornelius O.P., (New York: Crossroad, 1982), p. 341Google Scholar.

¹⁶ Aquinas’ view of quidditative knowledge is ably summarized by Gregory Rocca: “The quiddity of something is what something is. The definition is the intelligible meaning (ratio) that manifests or signifies the quiddity of something, revealing that thing's essence; and the definition is not just any meaning but the essential, categorical meaning specific to the entity in question. A lapidary sentence provides a summary statement: ‘A thing's definition is the meaning which the name signifies’ (meta 4.16.733). Quidditative knowledge, then, is essential, specific, definitional knowledge.”Rocca, Gregory P. O.P., Speaking the Incomprehensible God: Thomas Aquinas on the Interplay of Positive and Negative Theology (Washington, D.C.: The Catholic University of America Press, 2004), p. 30Google Scholar.

¹⁷ God is in no way limited because God is God's essence and as such God receives God's esse from no one. God has no potency and God participates in nothing. See S.T. I. q. 3 a. 4 corp.

¹⁸ I have borrowed the language of “absolutely transcendental properties” and “transcendental relative properties” from Norris Clarke in order to describe Aquinas’ treatment of attributes in terms of the transcendentals and in terms of the divine operation. See Clarke, The Philosophical Approach to God, pp. 83–88.

¹⁹ “That which the intellect first conceives as in a way, the most evident, and to which it reduces all its concepts, is being. Consequently, all other conceptions of the intellect [i.e. the other transcendentals] are had by additions to being.” St. Thomas Aquinas, De Veritate, q. 1 a. 1 corp.

²⁰ Clarke, The Philosophical Approach to God, p. 83.

²¹ S.T. I. q. 14 introduction.

²² For an excellent account of Aquinas’ development from his early discussions in the Scriptum super Libros Sententiarum and Summa contra Gentiles to his later account in the De Potentia and Summa Theologiae, see Wippel, John F. “Quidditative Knowledge of God” in his John Wippel, F., Metaphysical Themes in Thomas Aquinas, (Washington, D.C.: Catholic University of America Press, 1984), pp. 215–242Google Scholar.

²³ S.T. I. q. 3 introduction.

²⁴ Ibid.

²⁵ Aquinas maintains that relative names signify God's relation “to another (alium) or better another's relation to God's self.” (S.T. I. q. 13 a. 2 corp.)

²⁶ S.T. I. q. 13 a. 2 corp.

²⁷ The term “res”, which literally means “thing”, can be misleading here because it seems to be referring to the thing signified or the concrete referent of the attribute in a given judgment, but res significata simply refers to the attribute itself.

²⁸ Aquinas’ account of the modus signficandi can easily cause confusion. What the term precisely signifies is the mode of expressing the res significata. While we can predicate attributes of God that unqualifiedly designate a perfection (i.e. being, goodness, wisdom, etc.) our modes of expressing these perfections (i.e. abstract and concrete names) are imperfect in trying to signify the perfections of God in God's infinite simplicity. These modes of expressing these perfections betray their origin in our experience of finite and thus composed creatures in which the attribute and the subject of the attribute are not identical. God's essence (essentia), however, is God's existence (esse). Since God's perfections do not accidentally inhere in God, but are God the attribute and the subject of the attribute are identical. The only ways we, as finite creatures, can express the divine perfection is through abstract and concrete names. Through our use of abstract names (e.g. goodness), we can indicate that God is the attribute in God's simplicity. We can thus avoid any connotation of composition conveyed by the concrete name. Abstract names, however, are imperfect because they do not indicate that the perfection subsists. They do not convey “that which is, but that by which something is.” (S.C.G. I. 30) Concrete names (e.g. good), on the other hand, can be used to indicate that the perfection is or subsists, but here the perfection as concrete and determinate modifies a composed creature and thus fails to express the divine simplicity. Thus “in every name said by us, so far as concerns the mode of signification, there is found an imperfection which is not appropriate to God even though the attribute (res significata) in some eminent way befits God.” (S.C.G. I. 30) Although this is the precise meaning of modus significandi, there are two other elements that are implicitly involved in the modus significandi and are always explicitly operative in Aquinas’ analysis of the modus significandi. (See S.C.G. I. 30; S.T. I. q. 13 a. 1 ad. 2; De Potentia q. 7 a. 5 ad. 2; the latter does not explicitly treat the relationship between abstract and concrete names, as do the former texts, but simply maintains that the modes of signification are imperfect because they denote a definite form, which nevertheless is invoking the problem of concrete names.) The first element (mode of being) refers to the presupposition of all knowing and thus all naming and that is the imperfect way in which the res significata is concretely realized in the modes of being of particular finite things. The second (mode of knowing), follows upon the first and refers to the way we imperfectly come to know the res significata through its imperfect finite instantiation in particular finite things. For we only know the attributes through their finite instantiations in the world and we fall back upon these finite instantiation to exemplify anew the meaning of the res significata. Therefore, these two aspects are implicit elements within the intelligibility of the term modus significandi. (See S.T. I. q. 13 a. 1 corp.; S.T. I. q. 45 a. 2 ad. 2; De Potentia, q. 7 a. 5 corp.) Hence the foundation of the modes of expressing is the mode of knowing and the foundation of the mode of knowing is the modes of being. Thus all three elements are involved in Aquinas’ conception of the modus significandi.

²⁹ S.T. I. q. 13 a. 3 corp.

³⁰ Clarke, The Philosophical Approach to God, p. 72.

³¹ Clarke, W. Norris S.J., The One and the Many: A Contemporary Thomistic Metaphysics (Notre Dame, IN: University of Notre Dame Press, 2001), p. 49Google Scholar.

³² Ibid., p. 49.

³³ Ibid., p. 47.

³⁴ This is a paraphrase of the famous formula from the Fourth Lateran Council –“For between creator and creature there can be noted no similarity so great that a greater dissimilarity cannot be seen between them.” Tanner, Norman P., Decrees of the Ecumenical Councils Vol. I (London: Sheed & Ward; Washington, DC: Georgetown University Press, 1990)Google Scholar, Fourth Lateran Council, Constitution 2, p. 232.

³⁵ See S.T. I. q. 6 a. 3, S.T. I. q. 20 a. 1 ad. 3.

³⁶ The light of glory is an ontological determination of the knower that disposes her to receive the vision. This determination is the effect of the self-communication of God in the person's interiority. If the ontological communication of God to the creature is the condition of the possibility of the beatific vision, then God is the giver of the gift of vision, the giving of the gift, and the gift itself.

³⁷ In the beatific vision, since the mode of the object is not the mode of the knower the human being in vision knows God as infinite and as infinitely knowable but does not know infinitely. See S.T. I. q. 12 a. 7 ad 3.

³⁸ As Rahner correctly maintains, “What grace and vision of God mean are two phases of one and the same event which are conditioned by man's free historicity and temporality. They are two phases of God's single self-communication to man.” Foundations of Christian Faith, p. 118.

³⁹ The mystery or incomprehensibility of God, then “follows from the essential infinity of God which makes it impossible for a finite created intellect to exhaust the possibilities of knowledge and truth contained in this absolute fullness of being.”Rahner, Karl, ‘The Hiddenness of God’, in Theological Investigations XVI: Experience of the Spirit: Source of Theology, trans. Morland, David O.S.B. (New York: Crossroad, 1983), p. 229Google Scholar.

⁴⁰ Obediential potency, following the work of Karl Rahner, is the nature of the human being. The human being is a ‘potency’ because the human being as open to the totality of being, including God, is an openness, passive capacity, or receptivity for the self-communication of God. To preserve the gratuity of God's self-communication the modifier ‘obedential’ is employed. ‘Obediential’ indicates that this human nature is obedient to the special influence of God and that the human being would still be meaningful even if God did not communicate God's self. As such God's creation of human beings does not demand that God give God's self to them. God's self-communication is truly gratuitous.

⁴¹ Rahner, Karl, ‘Why does God Allow Us to Suffer?’ in Theological Investigations, v. 19: Faith and Ministry, trans. Quinn, Edward (New York: Crossroad, 1983), pp. 194–208Google Scholar.

⁴² A plurality cannot ground a unity. What grounds a plurality is precisely that which two or more things do not hold in common. As such that which they do not hold in common cannot ground the unity between them. When we distinguish A and B, we say that A is not B. This distinction or ‘not’ cannot ground the unity of A and B. A and B cannot be united unless they emerge from a prior unity or unless B as distinct from A emerges from A. If you are going to have unity and plurality, then the plurality has to originate from a prior unity.

⁴³ Karl Rahner, ‘Thomas Aquinas on the Incomprehensibility of God’, in Celebrating the Medieval Heritage: A Colloquy on the Thought of Aquinas and Bonaventure, ed. David Tracy, Journal of Religion 58 (Supplement, 1978), p. 124.

⁴⁴ Rahner, Karl, ‘The Concept of Mystery in Catholic Theology’, in Theological Investigations IV: More Recent Writings, trans. Smyth, Kevin (New York: Crossroad, 1982), p. 44Google Scholar.

⁴⁵ Karl Rahner, ‘Why does God Allow Us to Suffer?’ p. 206.

⁴⁶ Ibid., p. 206.

⁴⁷ Ibid., p. 206.

⁴⁸ Ibid., p. 206.

⁴⁹ Ibid., p. 206.

⁵⁰ This phrase has in mind T.S. Eliot's lines from East Coker of the Four Quartets “a raid on the inarticulate with shabby equipment always deteriorating.” Eliot, T. S., The Complete Poems and Plays 1909–1950 (New York: Harcourt Brace Jovanovich, 1952), p. 128Google Scholar.

⁵¹ An example of such an application of this understanding of mystery to a theological problem can be found in my “The Mystery of God and the Suffering of Human Beings”, Heythrop Journal L (2009), pp. 846–863. Here I show the range and limits of human knowledge of God and preserve the mystery of God in response to the problem of reconciling human suffering with the Christian belief in a God of infinite wisdom, power, and goodness.