From Divine Illumination to the Clearing of Being: Heidegger’s Ontological Turn in the Grounding of Truth Beyond Aquinas

Abstract

The problem of truth-grounding occupies a central position in the history of metaphysics. Aquinas synthesizes Aristotelian epistemology with the Augustinian doctrine of illumination, establishing a comprehensive system in which participation in the divine intellect, expressed through the illuminative function of the agent intellect, serves as the foundational principle. Heidegger, through a critical transformation of this system, opens an alternative path to the ontological grounding of truth. Rather than standing in simple opposition, the two thinkers stand in a relation of critical engagement. Heidegger preserves the phenomenological validity of the illumination metaphor, acknowledging the fundamental structure of truth as manifestation, while simultaneously dismantling the theological framework that undergirds its transcendent guarantee. In its place, he advances the ontological concepts of the clearing (Lichtung) and appropriation (Ereignis). This conceptual transformation marks a decisive shift in the grounding of truth: from dependence on the eternal assurance of a transcendent being to the historical self-disclosure inherent in Dasein itself.

1. Introduction

The problem of grounding truth runs through the entire history of Western metaphysics. To clarify the conditions and foundations of truth is not merely a central task of epistemology; it bears directly on how human beings understand their existential relationship with themselves and the world. On this question, Aquinas and Heidegger offer two responses that differ profoundly yet remain deeply intertwined. Aquinas synthesizes Aristotelian epistemology with the Augustinian doctrine of illumination, establishing a comprehensive system in which participation in the divine intellect, expressed through the illuminative function of the agent intellect, serves as the foundational principle. In Aquinas’s account, the human capacity for knowledge is secured through participation in the divine intellect, and intelligible forms ultimately correspond to the eternal archetypes (rationes aeternae) residing within the mind of God. His theological position holds that without the light of divine illumination, the human intellect is unable to attain truth.

Heidegger recognizes the historical significance of Aquinas’s theory, yet refuses to remain within its confines. His response is not outright rejection. Rather, he retains the insight that illumination discloses truth while stripping away its theological casing, relocating the ground of truth from the transcendent realm to Dasein’s being-in-the-world. Through such concepts as the clearing (Lichtung) and appropriation (Ereignis), Heidegger resituates truth on an ontological foundation. This article traces Aquinas’s theory of divine illumination, examines the dual dimensions of Heidegger’s inheritance and critique, and clarifies how Heidegger effects the transition in the grounding of truth from theology to ontology.

2. Aquinas’s Divine Illumination

Aquinas’s theory of truth rests on Aristotelian epistemological foundations, yet at critical junctures introduces the metaphor of illumination. Aristotle posits that human cognitive activity presupposes a dual structure of intellect. The passive intellect (intellectus possibilis) resembles a wax tablet: possessing no innate content of its own, it is nonetheless capable of receiving impressions from without. The active intellect (intellectus agens), by contrast, functions like light, transforming potentially intelligible objects into actually intelligible ones. As Cory demonstrates, Aquinas’s references to the mind’s abstractive activity as an “intellectual light” are “not metaphorical but rather technical, signaling that intellectual abstraction is to be modeled on the activity of physical light” (Cory 2015, p. 607). It should be noted that this characterization, which holds that ‘intellectual light’ is technical rather than metaphorical, pertains to Aquinas’s own epistemological framework. When this article subsequently refers to Heidegger’s engagement with the ‘illumination metaphor,’ the term ‘metaphor’ is used in a broader, phenomenological sense. It designates the way in which Heidegger appropriates the entire Western optical tradition, including its technically precise Thomistic form, as a phenomenological motif amenable to ontological transformation, independently of its original theological-metaphysical claims. This technical precision is what distinguishes Aquinas’s illumination account from a mere rhetorical inheritance of the Augustinian tradition. This analogy illuminates the core mechanism of cognition. Just as light renders potentially visible colors actually visible, the active intellect renders potentially intelligible forms actually intelligible.

The cognitive process unfolds through a series of transformative stages. The senses receive forms from external things, giving rise to sense impressions (phantasmata). “The phantasma is the product of the interaction between the sensory object and the sensory organ; it marks the completion of the sensible phase in which the known comes to be internalized within the knower” (Dong 2006, p. 39). These impressions do not yet constitute objects of intellectual cognition; they remain particular, concrete, and entangled with material conditions. The task of the active intellect is to abstract intelligible species (species intelligibilis) from these sense impressions. The precise character of this illuminative function has been a matter of scholarly debate. As Kintz argues, “the agent intellect neither extracts nor produces an intelligible species, but rather makes the nature that is already present in the object intelligible by actualizing its passive power of intelligibility” (Kintz 2019, p. 3). Only when the passive intellect receives these intelligible species does the formation of concepts occur. Cognition, however, does not terminate at this point. Aquinas insists that truth, strictly understood, resides not in the mere grasp of concepts but in judgment (iudicium) (ST I, 16.2).1 Simple apprehension (simplex apprehensio) grasps only the essence of a thing, as in asking “what is man?” At this level, questions of truth and falsity do not yet arise. It is judgment alone, the intellect’s act of composition and division (componendo et dividendo), that engages the existence of things and thereby admits of truth or falsity. When one asserts “Socrates is a man,” an existential relation is affirmed. When one asserts “Socrates is not a horse,” another is denied. Judgment constitutes the proper locus of truth precisely because it touches upon the existential dimension of things. This localization of truth in judgment rather than in simple apprehension accords with Martínez’s reading that, for Aquinas, “the most proper meaning of ‘truth’ is given in saying what a thing is and not in the apprehension of the species” (Martínez 2021, p. 4). This formulation underscores the existential rather than merely representational character of Thomistic truth. Yet this epistemological framework harbors a profound internal difficulty. If the active intellect is merely a faculty of the human soul, by what means does it guarantee the objectivity and universality of knowledge? The question admits of several formulations. Why are different individuals capable of apprehending the same truth? How can a particular, finite intellect grasp universal and necessary truths? When two persons both understand that the sum of the interior angles of a triangle equals 180 degrees, on what basis do their intellects arrive at such agreement?

Avicenna proposed a solution to this difficulty: the active intellect is not an internal faculty of the human soul but an external, separate entity, best understood as a kind of celestial intellect. Human cognitive activity consists in contact with, or irradiation from, this external intellect. The advantage of this position is that it provides an external guarantee of cognitive objectivity. Since all persons make contact with the same supra-individual intellect, the universality of knowledge acquires a firm basis. Aquinas, however, perceived a decisive weakness in this account.2 By externalizing the cognitive capacity, Avicenna deprives human beings of their status as genuine knowers in their own right. If the active intellect does not belong to the human person, can that person properly be called a knower at all? Aquinas’s response is to internalize the intellect as a faculty of the soul itself (potentia animae) (ST I, 79.1). He maintains that the active intellect genuinely belongs to the structural constitution of the individual human soul. Yet this internalization immediately generates a new difficulty: how does an internal intellect guarantee objectivity? If each person possesses his or her own active intellect, what prevents these intellects from yielding divergent cognitive results? In defending the epistemic subjectivity of the human person, Aquinas is compelled to address a further question: from what source does the internal active intellect itself derive, and on what basis does its cognitive capacity rest? It is in answering these questions that Aquinas moves beyond epistemology into ontology.

Aquinas’s revision of Avicenna’s account is not merely an epistemological adjustment; it involves a fundamental reconception of the ontological status of the active intellect. Avicenna understands the active intellect as an external, separate entity, and its advantage lies in ensuring that all human beings make contact with the same source of intelligibility, thereby securing cognitive objectivity. Yet, as noted above, this comes at the cost of epistemic subjectivity. Aquinas’s corrective position holds that the active intellect is genuinely a faculty of the soul itself, though this does not mean it is wholly independent of God. The key lies in the introduction of participation as a governing concept. This move also marks the precise point at which Aquinas’s account diverges not only from Avicenna but from the Augustinian-Bonaventurian illuminationist tradition, in which God functions as a separate efficient cause directly illuminating the human mind. For Aquinas, no such external divine intervention is required at the moment of cognition: the illuminating capacity belongs to the agent intellect as a genuinely human faculty, even though that faculty’s power derives ontologically from its participation in the divine intellect. The present article employs the concept of ‘divine illumination’ as a structuring term in this specifically Thomistic sense, that is, illumination through participation rather than through direct divine action. Participation is the pivotal term in Aquinas’s theory of truth, operating on two distinct levels. With respect to capacity, the active intellect possesses the power of illumination because it shares in the illuminating power of the divine intellect. In this respect, Culbreath has observed that “the notion of agent intellect as a participation in the divine light incorporates and synthesizes the various elements of these traditions, thereby bringing about a certain harmony between illuminationism and abstractionism” (Culbreath 2017, p. 2). This synthetic character is precisely what makes the doctrine of participation the structural key to Aquinas’s system. With respect to content, the intelligible forms that the human intellect obtains through abstraction ultimately correspond to the eternal archetypes (rationes aeternae) contained within the divine intellect. This correspondence is no mere coincidence; it reflects an ontologically necessary relation. Theological warrant for this position is found in Psalm 4:6: “Lord, who will show us good things? The light of your face is sealed upon us” (DV 16.3). For Aquinas, the human intellect is itself an imprint (signatum) of the divine light. This is not to say that the human intellect is directly identical with the divine intellect, which would be the error of pantheism, nor that human beings enjoy direct intuition of the divine intellect, which is the prerogative of the angels. It means, rather, that the human capacity for knowledge carries within itself the seal of the divine intellect, just as an impression in wax derives from the seal that stamps it.

Aquinas favors analogy as a means of clarifying the relation of participation. Air shares in the light of the sun: though air is not itself the source of light, it becomes luminous by receiving light. Creatures share in the existence of God: though no creature is being itself, each exists by virtue of divine creation. In the same way, the human cognitive capacity shares in the divine intellect: though the human intellect is not itself the divine intellect, it acquires through this participation the ability to know truth. The relation of participation thus serves a double function. It secures the genuine reality of the human cognitive capacity, since that capacity truly belongs to the human person, while simultaneously providing an ultimate foundation for its objectivity, since that capacity derives from the divine intellect. The ontological consequences of the doctrine of participation unfold further in the theory of eternal archetypes (rationes aeternae). For Aquinas, every created thing has a corresponding idea in the divine intellect (ideae in mente divina) (DV 19.2). These ideas constitute the exemplary causes (exemplar) of all things and are the source of all truth (causa veritatis). From this follows a structure of double conformity. Created things conform to the divine ideas: this is the truth of things (veritas rei). The transcendental dimension of this structure has been carefully analyzed by Ueeda, who notes that “the term verum expresses the common aspect of real beings which the term ‘being’ does not express and the aspect is that any being corresponds to the knowing power of our soul” (Ueeda 1996, p. 2). This transcendental relational character is precisely what allows Aquinas to ground the double conformity of veritas rei and veritas intellectus within a single ontological framework.

The human intellect conforms to created things: this is intellectual truth (veritas intellectus). The human intellect, through the mediation of created things, conforms indirectly to the divine ideas. Aquinas does not hold that human beings can know the divine ideas directly. Such direct intuition belongs to the angels, or to the soul’s beatific vision (visio beatificans) in the life to come (ST Suppl, 92.1). In the present life, human cognitive activity depends necessarily on sense experience, proceeding by way of abstraction from sense impressions. Yet in knowing created things, the human intellect indirectly makes contact with the eternal archetypes. This contact is not a form of mystical intuition but rather an encounter with the traces of the divine ideas reflected through the formal structure of created things. It is precisely these eternal archetypes that guarantee the objectivity, universality, and necessity of truth, for they are themselves eternal and immutable, rooted in the very essence of the divine intellect.

The most fundamental problem confronting Aquinas’s theory of truth is what might be called the paradox of finitude. Schultz-Aldrich has shown that “for Aquinas, human knowledge of composite beings is attained through encounters with their real instances and is reflected in necessarily true yet nonanalytic statements about these creatures” (Schultz-Aldrich 2009, p. 620). This observation clarifies why finite, contingent beings, despite their mutability, can serve as legitimate if incomplete grounds for the human grasp of necessary truth. Created things are contingent, mutable, and finite; they cannot of themselves guarantee the necessity and eternity of truth. A stone may exist or not exist; a tree grows and withers; all things stand in a state of perpetual becoming. If truth were grounded solely in such changeable realities, its necessity and universality would remain in doubt. The human intellect is equally finite and fallible. Individual cognitive capacities differ from person to person, conditioned by heredity, education, historical circumstance, and a host of other factors. Human reason alone cannot establish absolutely certain truth. How, then, can finite knowers knowing finite things give rise to universal and necessary truth? Consider the mathematical proposition “1 + 1 = 2,” which holds with absolute necessity regardless of time, place, or the particular knower. Neither finite human reason nor variable sense experience can independently account for the source of this necessity. Aquinas’s answer is that an infinite being must serve as its ultimate guarantee. Only what is eternal, immutable, and infinite can provide the ultimate foundation for necessary truth. The divine intellect alone possesses this eternity (ST I, 16.7).

In Aquinas’s theological metaphysics, God is not merely the creator of all things but the prima veritas, first truth, or veritas ipsa, truth itself. The theological stakes of this position are considerable. As Cuddeback argues, “divine illumination, God’s governance of our natural knowledge of truth, brings to bear on our truth-knowing the authority of God as First Truth. The effect of divine illumination is that every one of our truth-judgments is a participated act of authority” (Cuddeback 2009, p. 579). This claim is grounded in the essential constitution of God. God’s existence and essence are identical (esse = essentia); that is, God’s essence just is existence itself. Equally, God’s intellect and existence are identical (intellectus = esse); God does not possess intellect but rather is intellect itself. From this identity it follows that God is truth itself. The relation between God and created truth may be understood along three dimensions. God is the causa, the cause of all truth: all truth ultimately derives from God’s creative and intellectual activity. God is the exemplar, the exemplary cause of all truth: the eternal ideas in the divine intellect constitute the archetypes of all things and the ultimate standard to which human knowledge must conform. God is the mensura, the measure of all truth: the standard of truth resides not in the human intellect, nor in mutable things, but in the eternal and immutable divine intellect. The act of creation plays a central role in this grounding of truth. God creates all things according to the ideas in his intellect, and the “truth” of a created thing consists precisely in its realization of God’s creative intention. An oak tree is a “true” oak tree insofar as it conforms to the idea of “oak tree” in the divine intellect; human knowledge is “true” insofar as it conforms to created things and thereby conforms, indirectly, to the divine ideas. In this way, the foundation of truth is elevated from the contingent realm of creation to the necessary divine intellect, traced back from the mutable world of appearances to the immutable eternal archetypes.

At this point, Aquinas’s system of truth-grounding takes the form of a complete, hierarchically ordered chain of guarantee. At its apex stands God, first truth and truth itself. Through the act of creation, God confers truth upon created things, and the truth of things consists of nothing other than the actualization of the divine ideas. Created things act upon human cognitive capacity through sense impressions, activating the illumination of the active intellect; this illumination is itself a participation in the divine intellect. The active intellect obtains intelligible species through abstraction. The intellect then forms judgments on the basis of these intelligible species, yielding propositional truth, namely the conformity of intellect to created things. Propositional truth presupposes the acquisition of intelligible species; intelligible species presuppose the illuminating power of the active intellect; the illuminating power of the active intellect derives from participation in the divine intellect; and the divine intellect, as first truth, is the uncaused first cause (causa prima), which is itself without dependence on any prior being, since in God essence and existence are identical (esse = essentia) and he subsists as pure act (actus purus) requiring no external principle. The chain terminates in God, forming a complete and self-enclosed metaphysical whole. It should be noted that Aquinas explicitly rejects the notion of causa sui (a cause of itself) on the grounds that a cause is ontologically prior to its effect; God is not self-caused but rather the ipsum esse subsistens whose existence requires no further ground.

Within this system, Aquinas also addresses the relation between faith and reason. He explicitly rejects the view, current in his time, that philosophical truth and theological truth can contradict each other. In his account, the truths attained by natural reason and the truths disclosed by divine revelation share a common source in the divine intellect and therefore cannot genuinely conflict (ST I–II, 109.1). The distinction is only this: certain truths, such as the existence of God and the immortality of the soul, are accessible to natural reason, while others, such as the Trinity and the Incarnation, exceed the capacity of reason and require the assistance of faith. To exceed reason, however, is not to contradict it; the latter is impossible, since reason itself is a gift of God. This unity confirms once more that in Aquinas’s theory of truth, reason and faith, philosophy and theology, ultimately converge upon the same theological foundation: divine illumination.

3. Heidegger’s Twofold Attitude Toward the Doctrine of Divine Illumination

Heidegger’s engagement with Aquinas’s doctrine of divine illumination neither simply discards the traditional conception of truth nor settles for patching it up within a medieval metaphysical framework. What deserves particular attention is that Heidegger consistently treats Aquinas as a serious interlocutor on the question of truth-grounding. In Aquinas’s doctrine of illumination, he identifies a genuine philosophical insight: that the question of truth must be clarified on a more originary basis that exceeds the level of propositional analysis. At the same time, he firmly rejects Aquinas’s resolution of this issue by recourse to the divine intellect. This complex theoretical posture is precisely what constitutes Heidegger’s twofold attitude toward Aquinas. He retains the phenomenological legitimacy of “illumination” as a structural concept while radically reversing the direction of its source; he acknowledges the theoretical impulse to seek a metaphysical grounding for truth while replacing the theological-transcendent framework with the existential-ontological determinations of Dasein.

3.1. Affirming the Phenomenological Insight of “Illumination”

Heidegger does not abandon the ancient metaphor of illumination. Within his terminological apparatus, Lichtung (clearing), lichten (to clear, to illuminate), and related concepts continue to occupy a central position. This is no arbitrary choice of vocabulary but a deliberate appropriation of the Western philosophical tradition of optical metaphor. Heidegger recognizes that from Plato’s allegory of the cave to the medieval doctrine of illumination, Western philosophy has persistently employed “light” to articulate truth, and that this tradition captures something genuine: that truth essentially involves a process of bringing things to manifestation.

In Being and Time, Heidegger makes a decisive claim about the mode of being of Dasein: Dasein, “as Being-in-the-world, is ‘cleared’ (gelichtet)” (Heidegger 1962, p. 171). Subsequent formulations retain the noun licht (light) within this context. Heidegger does not discard the illumination metaphor; he transforms it, investing it with a new ontological content. He elaborates: “Dasein is its disclosedness” (Heidegger 1962, p. 171). This claim discloses the double character of Heidegger’s relation to the metaphor of illumination. He retains the language of ‘clearing’ while fundamentally reconceiving the character of clearing and how it occurs. Since Dasein is the clearing rather than an agent that performs it, un-concealment happens at a level more fundamental than any deliberate act or choice, even though particular actions can be illuminating or concealing. Aquinas’s lumen naturale intellectus, the natural light of the intellect, is reinterpreted by Heidegger as an existential-ontological structure of Dasein. “In ontical talk,” Heidegger writes, “we sometimes use the expression ‘being illuminated’ to describe what we mean when we speak of the lumen naturale in man. This means nothing other than the existential-ontological structure of this entity, that it exists in such a way that it is its own ‘there’” (Heidegger 1962, p. 167). The decisive point in this passage is that Heidegger does not reject Aquinas’s concept of the natural light but reinterprets it as an ontological structure of Dasein. The metaphor of illumination is preserved, but the source of illumination is relocated from the external divine intellect to Dasein’s own being-in-the-world. This preservation is not mere terminological continuity; it is the extraction of the phenomenological core from a traditional metaphor. What the metaphor of illumination captures, as Heidegger sees it, is the basic character of truth’s occurrence: bringing what is concealed into the open, actualizing what is potential, rendering visible what was invisible. In Aquinas, the illumination of the active intellect transforms potentially intelligible objects into actually intelligible ones; in Heidegger, the clearing (Lichtung) brings beings out of concealment (Verbergung) into openness (Offenheit). At this level, the two thinkers share a deep phenomenological resonance.

Heidegger’s preservation of the illumination metaphor reveals a point of phenomenological convergence between himself and Aquinas. Both thinkers recognize that truth is not a static, ready-made property but involves a dynamic process of bringing things to manifestation. Light renders what is hidden visible, what is obscure luminous, what is invisible perceptible. This is precisely the essence of truth as ἀλήθεια: un-concealment. What Heidegger undertakes is not an abandonment of this insight but a stripping away of its theological casing, restoring it to a purely ontological description. Beyond acknowledging the phenomenological legitimacy of the illumination metaphor, Heidegger also aligns with Aquinas at a deeper level of theoretical orientation. Both thinkers reject the adequacy of surface-level analyses of propositional truth and press instead toward the ontological foundation of truth. For Aquinas, truth cannot be reduced to the external relation of “conformity between proposition and fact”; it presupposes the intellect’s power of illumination, which in turn presupposes participation in the divine intellect. For Heidegger, truth likewise cannot rest at the level of propositional correctness; it presupposes the prior disclosure of beings, which is itself rooted in the structure of disclosedness belonging to Dasein. What unites these two positions is the refusal to be satisfied with describing the outward features of truth, and the insistence on pressing toward its inner foundation. Heidegger acknowledges this theoretical depth in the traditional conception of truth when he states in Being and Time: “The definition of truth that we have proposed is not a shaking off of the tradition, but a primordial appropriation of it” (Heidegger 1962, p. 265). This appropriation is not simple acceptance. It is a critical inheritance that retains the phenomenological insight of the tradition while simultaneously disclosing its ontological ground.

Heidegger’s inheritance of the illumination theory, however, operates within strict limits. He retains ‘illumination’ only as a phenomenologically repurposed concept: what functioned as a technical term within Aquinas’s participatory metaphysics is stripped of its theological scaffolding and retained solely as a structural motif naming the occurrence of disclosure, not as a metaphysical claim about divine power. The decisive shift occurs at the level of the question itself. Aquinas asks, “who illuminates?” and the answer points toward a transcendent source, namely God. Heidegger asks, “how does manifestation occur?” and the answer points toward the ontological structure of manifestation itself. This transformation in the mode of questioning marks a fundamental transition from theological metaphysics to ontological phenomenology.

3.2. Heidegger’s Critique of Aquinas’s Doctrine of Divine Illumination

Heidegger’s critique of Aquinas’s doctrine of divine illumination targets its theological-transcendent foundation. The critique operates across three registers: epistemological, ontological, and theological. The complexity of Heidegger’s engagement with Aquinas has been noted in the secondary literature. Orr identifies three central criticisms made by Heidegger of Aquinas’ conception of truth, which posits a subject-oriented and representationalist theory of knowledge, an unwarranted intellectualism, and an ontotheological grounding of truth’s objectivity, while observing that these criticisms “paradoxically expose vulnerable flanks in his own constructive account” (Orr 2014, p. 1). This paradox is worth bearing in mind as we trace the dual movement of Heidegger’s inheritance and critique.

In the top-down structure of Aquinas’s doctrine as reconstructed by Heidegger, illumination flows from without, and the capacity for illumination is ultimately derived from the divine intellect rather than constitutive of Dasein’s own being. It must be acknowledged that describing the human knower as a ‘passive recipient’ does not accurately characterize Aquinas’s own account: as the foregoing analysis makes clear, Aquinas assigns genuine activity to the human intellect through the intellectus agens. However, from Heidegger’s critical perspective, even this active cognitive capacity is, at the ontological level, derivative, grounded in participatio in the divine intellect rather than in any structural feature of Dasein itself. It is in this specific sense of ultimate ontological dependence on a transcendent source that the language of dependence is employed here. This relation of dependence constitutes the theological basis of Aquinas’s theory of truth. Heidegger’s critique of this structure is thoroughgoing. His central argument is that it is not God who illuminates the human being but rather Dasein itself that is “cleared” (gelichtet). The clearing belongs to Dasein’s mode of being as such; it does not arrive from outside but is an ontological structure of Dasein itself. This claim fundamentally overturns the basic presupposition of the traditional illumination theory. That theory invariably presupposes a pre-existing knower, the human soul or intellect, which is subsequently illuminated by an external source, the divine intellect. For Heidegger, Dasein is not from the outset a closed, darkened subject awaiting illumination from without. On the contrary, Dasein’s very mode of being is being-in-the-world (In-der-Welt-sein): open, and already cleared. This openness is not a capacity acquired through experience, nor a gift bestowed by some external being; it is the ontological structure of Dasein’s mode of existence. Heidegger calls this structure disclosedness (Erschlossenheit).

Disclosedness comprises three fundamental moments: attunement, understanding, and discourse. Attunement means that Dasein always already finds itself in some Stimmung, some mood, whether anxiety, fear, joy, or boredom. These moods are precisely the ways in which the world is disclosed to Dasein: in anxiety, the world appears uncanny; in joy, it appears welcoming. Understanding means that Dasein always already understands being, not through theoretical cognition but through a projective “being-able” oriented toward possibility. I understand a hammer not because I have mastered its definition but because I grasp that it can be used to drive a nail. Discourse means that Dasein always already dwells in meaning; the articulation of meaning enables Dasein to “speak of” the world. Together, these three moments constitute what Heidegger calls the clearedness (Gelichtetheit) of Dasein.

Through this analysis, Heidegger dissolves the necessity of positing a transcendent being as the source of illumination. If Dasein’s own mode of being is already open and already cleared, no external light is required to illuminate it. God as the “light source” becomes redundant. The top-down chain of illumination that Aquinas constructs from the divine intellect to the human active intellect is negated step by step. The conditions of possibility for truth shift from the external to the internal, from theology to ontology, from grace to the existential structure of Dasein itself. The deeper philosophical significance of this critique lies in a relocation of the very question of the source of illumination. Aquinas asks: from where does light come? The answer is: from God. Heidegger presses further: why must one ask from where light comes at all? If Dasein itself is the clearing, the question of a “source of illumination” is itself a pseudo-question. Light does not “come” from anywhere; the clearing is not bestowed by any being. Dasein’s mode of existence simply is openness, simply is luminosity. This reversal is not a substitution of “Dasein” for “God” as a new light source; it is the cancelation of the very metaphysical posit of a “light source.”

The second pillar of Aquinas’s doctrine of divine illumination is the theory of eternal archetypes. As noted above, the eternal ideas in the divine intellect constitute the exemplary causes of all created things and the source of all truth. These eternal archetypes guarantee the immutability and necessity of truth. Within this framework, time appears as the adversary of truth: flux, change, and contingency are forms of deviation from eternal truth. Genuine truth subsists in an eternity that transcends time, and human cognition in time amounts to no more than a provisional grasp of what is eternally true.

Heidegger’s critique of this conception is radical. In his view, truth is not eternal but historical. Truth as un-concealment (aletheia) is not the reflection of some supra-temporal idea but an occurrence (Geschehen), and each historical period has its distinctive “truth of being.” This claim presupposes Heidegger’s specific understanding of historicity (Geschichtlichkeit). Historicity is not history in the chronological sense (Historie), not an accumulation of past events or a chain of causes and effects, but historical occurrence in the ontological sense (Geschichte). In Being and Time, Heidegger already begins to disclose the historical character of truth. He explicitly opposes the understanding of truth as “eternal”: “The supposition of ‘eternal truths’ will not be adequately grounded until it has been successfully proved that Dasein has been and will be for all eternity.” He likewise asserts that “the phenomenon of truth always appears in the sense of disclosedness.” Together these two claims constitute a twofold critique of the eternal conception of truth. First, truth is not eternally present. Second, truth must be wrested from concealment; it is a process of struggle, not a ready-made possession. The very prefix ent in Entbergen (un-concealment) indicates that truth is the result of being wrested free from a prior state of concealment. This is a dynamic and ongoing process, not a static and unchanging condition.

In his later thought, Heidegger develops this insight into the theory of Ereignis (appropriation). Ereignis is not an event in the ordinary sense (ein Ereignis) but the event of appropriation as such (das Ereignis), the historical manner in which being gives itself. In the Contributions to Philosophy (1936–38), Heidegger states: “Being appropriates Da-sein, and only because Da-sein is appropriated as the grounding-attunement does being hold sway” (Heidegger 2016, p. 302). This means that being is not eternally present but gives itself in and through history. Each epoch has its distinctive destining of being (Geschick des Seins): the physis (self-emergence of nature) of the Greek world, the creatio (divine creation) of the medieval world, the subjectum (subject of representation) of modernity, and the Gestell (enframing) of the contemporary technological age. The medieval truth-horizon in which Aquinas worked, where truth means the order of created things conforming to divine ideas, represents just one among many historical forms through which being sends itself; it is not the singular, eternal truth.

The deeper target of this critique is the privileging of eternal, self-identical presence as the paradigmatic mode of being, which scholars following Derrida have termed the ‘metaphysics of presence,’ though Heidegger’s own preferred formulations for the same error include Onto-Theologie and the reduction of being to ständige Anwesenheit (constant presence).”3 The doctrine of eternal archetypes presupposes a pure, supra-temporal presence in which truth perpetually maintains its self-identity. Heidegger regards this presupposition as the foundational error sustained throughout Western metaphysics from Plato to Hegel. Truth, on his account, arrives and withdraws historically. From this Heidegger draws the further claim that truth is vulnerable to concealment and oblivion. In Aquinas’s framework, truth enjoys the eternal guarantee of the divine intellect; human intellectual truth may err, but truth within the divine intellect is absolutely reliable. Heidegger contends, by contrast, that truth can be concealed and forgotten. The “forgetting of being” (Seinsvergessenheit) characteristic of the modern technological age is itself proof that no eternal guarantee of truth exists. When everything is reduced by technological enframing to calculable resources, the originary meaning of being falls into oblivion. Truth requires custodianship rather than automatic assurance. The human being is no longer the passive recipient of truth but its guardian.

The third register of Heidegger’s critique targets the residual representationalism in Aquinas’s epistemology. Aquinas is not a subject-philosopher in the modern sense, and he does not, like Descartes, ground all knowledge in the cogito. Yet his epistemological framework retains the basic structure of representationalism. This is most evident in the concept of the species intelligibilis. In Aquinas’s account, the species intelligibilis plays the role of a crucial intermediary. External things act upon the senses to produce sense impressions; the active intellect abstracts intelligible species from these impressions; the passive intellect receives these species and forms judgments. For Aquinas, the essence of truth consists in the adequation of thing and intellect. As he states in the Summa Theologiae: “veritas est adaequatio intellectus” (ST I, 16.1), the adequation of intellect to thing, not of the intelligible species to the external thing. The species intelligibilis functions as the cognitive medium through which the intellect is formally assimilated to the thing; it is not itself the relatum of the truth-relation but the means by which the intellect achieves conformity with reality. The characterization of Thomistic epistemology as ‘representationalism’ reflects Heidegger’s critical reconstruction rather than Aquinas’s own self-understanding. For Aquinas, the species is not a Cartesian inner image standing between mind and world; it is a formal likeness (similitudo) through which the intellect becomes identical in form with the thing known. Whether Heidegger’s critique of the species intelligibilis as a mediating representation accurately captures Aquinas’s position is contested in the secondary literature (Orr 2014, p. 1). The present article follows Heidegger in treating the species as a mediating structure to be overcome by his phenomenology of direct disclosure, while acknowledging that this reading of Aquinas is not uncontroversial.

Heidegger’s critique of this mediating structure is thoroughgoing. Cognition, he argues, does not operate through the intermediary of “representation” but discloses the being itself directly. The function of a proposition is “to let the entity be seen from itself, to exhibit the entity, to ‘show’ it” (Heidegger 1962, p. 261). This “letting-be-seen” is directed not toward an inner species but toward the being itself. Heidegger discloses this through a phenomenological analysis of the concept of conformity. He observes that while all conformity is a relation, not every relation is conformity. The reference of a sign to what it signifies is a relation, but this reference is not itself a conformity between sign and signified. Equally, the relation between a proposition and the being it intends is not the “resemblance” or “reflection” of a representation to what it represents. Heidegger states explicitly: “If the agreement has the character of one being (a subject) assimilating itself to another (an object), then the structure of truth cannot be that of agreement between a knowing subject and an object” (Heidegger 1962, p. 261). This means that the Thomistic model of “species conforming to external thing” is comprehensively rejected. Heidegger returns instead to the more originary situation of Dasein’s being-with beings. Prior to theoretical cognition, Dasein is already engaged with beings. This primordial mode of engagement is practical.

In sections 15 and 16 of Being and Time, Heidegger develops a careful distinction between the readiness-to-hand (Zuhandenheit) and the presence-at-hand (Vorhandenheit) of equipment. A hammer is not first “represented” as an object and then put to use; rather, its “hammer-character” is disclosed in use, in the practical nexus, as the mode of being of a ready-to-hand thing. Readiness-to-hand is primary; the object-like presence-at-hand characteristic of theoretical observation is derivative. Only when a piece of equipment breaks down, as when a hammer suddenly snaps, does it stand out from the practical nexus and become an object of observation. Theoretical cognition is a secondary act of abstraction that presupposes the prior practical being-in-the-world. Heidegger draws the conclusion that adaequatio is a derivative form of truth, one that presupposes the prior manifestation of beings within Dasein’s world. Originary truth is not conformity but the open domain co-constituted by Dasein and world. In On the Essence of Truth, Heidegger formulates this insight as follows: “The question of the essence of truth in the sense of the un-concealment of being is the question of the essential history of the human being as ek-sistent” (Heidegger 2008, p. 140). From this it follows that the knower-known opposition that characterizes traditional epistemology is dissolved; truth shifts from the “epistemological” to the “ontological,” from the “correctness of representation” to the “un-concealment of being.” Aquinas understands truth as the relation between the intellect and the thing, mediated by the species. Heidegger contends that prior to this subject-object opposition there is a more originary structure: Dasein’s being-in-the-world. Dasein does not first exist as a closed subject and then come to know external objects through the mediation of species; from the outset, Dasein is in the world, co-present with beings, and the world is already disclosed to it in meaning.

Through this threefold critique of the source of illumination, the doctrine of eternal archetypes, and the intermediary of representation, Heidegger deconstructs the theological-transcendent foundation of Aquinas’s theory of truth. Traditional metaphysics grounds truth in a transcendent, eternal, and external being, namely God; Heidegger resolves truth into the historical, internal, and existential structure of Dasein itself. Heidegger does not, however, rest content with critique. Deconstruction is not the end; reconstruction is its ultimate purpose. Having dismantled the theological-transcendent foundation, Heidegger faces the corresponding theoretical task of establishing a new ontological ground for truth, one that dispenses with the need for transcendent support.

4. Heidegger’s Ontological Reconstruction of Truth-Grounding

Having dismantled the theological-transcendent foundation of Aquinas’s doctrine of divine illumination, Heidegger confronts an immediate question: if truth no longer requires a transcendent ground, on what does it stand? His answer is the clearing (Lichtung). Yet this is not a substitution of a new “ground” for God but a transformation of the very question of grounding itself. Heidegger does not ask what the ground of truth is, which would remain a metaphysical mode of inquiry, but rather how truth opens itself in the clearing, which is an ontological mode of description. This shift marks the opening of the constructive dimension of Heidegger’s theory of truth.

Heidegger’s choice of the German word Lichtung to express his understanding of how truth occurs is itself philosophically significant. In ordinary German, Lichtung is a forestry term designating the open space formed when trees are felled or naturally recede. Heidegger likens the clearing to a forest clearing, and this compact description encapsulates his fundamental transformation of the traditional doctrine of illumination. In the traditional theory, brightness comes from an external source of light, whether the Platonic “sun” or the Thomistic “divine intellect.” Light issues from the source, falls upon an object, and transforms it from dark to bright. This is a linear structure running from light source through light ray to illuminated object. In the image of the forest clearing, however, brightness does not come from an external luminary. The brightness of the Lichtung comes from the recession of the trees, from clearance, the making of room, which is ontologically prior to any illumination that follows. As Heidegger states: “Light never creates openness. Rather, light presupposes openness” (Heidegger 1972, p. 65). It is precisely the absence of trees and the withdrawal of what had concealed that allows the clearing to form and sunlight to enter. This insight contains a fundamental transformation of the concept of illumination. It is not a luminary (God) that illuminates an object (an intelligible form); rather, an open domain makes manifestation possible. This is not a simple substitution of one metaphor for another but a transition from the binary structure of source and object to the generative structure of open domain and manifestation. In the former, one must always ask from where light comes, and the answer necessarily points toward a transcendent being. In the latter, “light” requires no source, because the clearing is itself the open space, the domain that makes manifestation possible. This does not entail that truth requires no ground whatsoever. A distinction is necessary between two senses of grounding: (i) grounding as the identification of a transcendent being that causally or exemplarily accounts for truth; and (ii) grounding as the phenomenological description of the structural conditions within which truth can occur. Heidegger abolishes grounding in sense (i) while retaining it in sense (ii). The ‘source’ he denies is a being functioning as causa efficiens or causa exemplaris; what he affirms is the clearing (Lichtung) as the ontological domain of disclosure, which is abgründig (without a being above it) but not equivalent to the absence of all structural conditions for truth.

The most difficult and most original claim in the ontological structure of the clearing is that the clearing essentially contains concealment. For Heidegger, concealment is not the opposite of the clearing but its intrinsic constituent. This is not a contingent empirical fact but an ontological necessity. Manifestation necessarily accompanies non-manifestation. When a forest clearing is illuminated, we see the things within it, but the surrounding forest remains in shadow. Every illumination entails a region that remains unilluminated; every disclosure entails dimensions that remain undisclosed. This is not a matter of illumination being insufficiently complete; it is the ontological structure of disclosure as such. Heidegger distinguishes two modes of concealment. The first is refusal. Beings refuse full disclosure, retaining a certain impermeability. Another person presents face, speech, and conduct, yet the depths of that person’s interiority can never be fully opened. A stone presents its hardness, color, and shape, yet its “stone-character,” its participation in the inexhaustibility of the earth, refuses to be exhausted by theoretical cognition. The second mode of concealment is dissemblance (Verstellen). Beings appear in the guise of something else, and the appearing is itself a form of concealment. The social pleasantries of polite company both present a self and conceal the actual self; the advertisement for a commodity both displays the product and conceals its genuine use-value (Heidegger 2004, p. 40). It follows, in Heidegger’s account, that un-truth (Un-wahrheit) belongs to the innermost essence of truth. This is not to say that there is no truth or that everything is false; it is to say that the occurrence of truth essentially involves concealment. The structure of the Greek word ἀλήθεια itself discloses this: ἀ- (privative prefix) combined with λήθη (concealment, forgetting) yields un-concealment.4 Truth is liberation from concealment, but this means that concealment, as that which truth must overcome, is always already present. Truth is not the termination of concealment but an ongoing struggle against it.

In The Origin of the Work of Art, Heidegger writes: “With regard to the essence of truth, the opposition between clearing and concealing that holds sway within truth’s essence may be named as the concealing refusal. This is the primordial conflict” (Heidegger 2004, p. 41). This “conflict” (Streit) is not a binary war of opposites but a tension of mutual dependence. Heidegger takes the Greek temple as his example. The temple “sets up a world,” encompassing the Greeks’ sacred order, their way of life, their totality of meaning. Within this world, beings are brought into the clearing. Simultaneously, the temple “sets forth the earth,” letting rock appear as rock, letting the weight, solidity, and impermeability of stone come to appearance. In this setting-forth, the obscurity and inexhaustibility of the earth are preserved. The strife between world and earth is the strife between clearing and concealment. This strife has no terminus, nor should it, for it is the very manner in which truth “occurs.” Truth is not a static conformity but a dynamic strife, perpetually in the process of coming to be.

In his account of the clearing, Heidegger insists that it is neither static nor eternal. The clearing itself occurs historically, unfolding in different ways in different epochs. This brings us to the concept of Ereignis (appropriation). In ordinary German, Ereignis simply means “event,” but Heidegger invests it with a distinctive philosophical sense. He distinguishes between ein Ereignis, a particular event such as a wedding or a war, and das Ereignis, appropriation as such, the manner of “occurring itself.” Heidegger traces the etymology of the word: eigen means “own” or “proper”; er-eignen means “to appropriate” or “to make one’s own.” Ereignis thus names not a particular occurrence but the occurrence of the mutual belonging of being and Dasein. In the Contributions to Philosophy, Heidegger advances a central claim: “Be-ing essentially occurs as the event of appropriation (das Seyn west als das Ereignis)” (Heidegger 2016, p. 38). The word west here does not carry the static force of ist (“is”) but the dynamic force of “essentially occurs.” Being is not eternally present; it “gives itself” in and through Ereignis.

Heidegger’s analysis of the German idiom Es gibt Sein (literally “it gives being,” usually rendered as “there is being”) discloses the deeper import of Ereignis. He draws attention to the verb geben (to give), ordinarily overlooked in this phrase. The “Es,” he argues, is not any being, nor even a grammatical subject in the usual sense. Es gibt does not mean “there is a something that gives”; it means that “giving itself” is occurring. This is analogous to Es regnet (“it is raining”): the phrase does not assert that “sky” as a subject is performing the action of raining but simply that raining is happening. Equally, Es gibt Sein does not posit an agent that bestows being; it means that “giving” itself is the manner of being’s occurrence. Ereignis is, in this sense, the occurring of giving itself.

If being “gives itself” in and through Ereignis, then for Heidegger, being sends itself in different ways in different historical epochs. The German word Geschick carries a double sense: “fate” or “destiny” on one hand, and “sending” on the other, derived from the verb schicken, to send or dispatch. The history of being, Heidegger contends, is not the history of human subjective activity, nor the unfolding of an objective causal chain; it is the history of being’s self-sending. In ancient Greece, being sent itself as physis (self-emerging nature). In the medieval world, it sent itself as creatio (divine creation). In modernity, it sent itself as subjectum (the subject of representation). In the contemporary technological age, it sends itself as Gestell (enframing). Heidegger’s account of these four epochs is not a chronological record but an ontological typology. The truth of each age is the outcome of being’s self-sending in a specific mode. From this conception of the history of being, Heidegger draws a further claim of some consequence: truth is fragile and subject to forgetting. Truth can be concealed and forgotten to an extreme degree. In certain passages, Heidegger raises the more radical possibility that modern humanity may not yet have become Dasein in the full sense, or may risk ceasing to be so. In such a situation, the structural condition of disclosure itself would be imperiled. Short of that limit, however, truth as disclosure remains structurally available wherever Dasein exists, even as its originary meaning may be thoroughly covered over.

Heidegger notes that enframing is itself a mode of clearing, though an extreme and exclusionary one. It reduces everything to standing-reserve (Bestand): resources that are storable, deployable, and calculable. More perilously, the people of the modern age have lost awareness of this concealment. When everything is technologically disclosed as “calculable resource,” being is concealed and thoroughly forgotten. This is what Heidegger calls “the forgetting of forgetting itself.” Yet Heidegger is no pessimist. He returns repeatedly to Hölderlin’s verse: “But where danger is, grows/the saving power also” (Heidegger 2018, p. 28). When the dominion of technology reaches its extreme and everything is reduced to calculability, there may arise a questioning of whether this is the only manner of being’s occurrence. That questioning is itself a recollection of being, an opening toward another beginning. This turning, however, does not arrive of itself; it requires human participation and human guardianship.

The concept at the center of Heidegger’s understanding of guardianship is Seinlassen, letting beings be. Sein means “being” or “to be”; lassen means “to let,” “to allow,” or “to enable.” The “letting” in “letting beings be” is not the indifference of everyday permissiveness. Heidegger draws a clear distinction between Seinlassen and Fahrenlassen, abandonment or letting-go. Abandonment means indifference and unconcern, a disengaged “just let it go.” Equally, Seinlassen is not subjective arbitrariness, not the relativism that holds that “anything goes.” Heidegger illustrates the contrast between Seinlassen and the technological attitude through a concrete example. Confronted with a tree, the technological attitude, the attitude of enframing, regards the tree as a timber reserve. The truth of this tree is its calculable yield of lumber, its economic value, its industrial applications. The tree is commandeered as an exploitable resource; its existence is entirely reduced to exploitability. The attitude of Seinlassen is different. It does not refuse to use timber; rather, while using timber, it also sees the tree’s growing, flowering, and withering, it sees the shelter it provides for birds, and lets the tree appear as a tree. For Heidegger, the human being is able to let beings be because the human being itself ek-sists (ek-sistieren) within the clearing of being. One does not first exist as a closed subject and then acquire the capacity for freedom; from the outset, one stands in an openness oriented toward being. This freedom is the manner in which the clearing occurs in the human being, and it is the fundamental manner in which the human being guards the clearing.

In the contemporary technological age, the task of guarding the clearing is especially urgent. Enframing holds dominion over everything, and its mode of clearing conceals the other possibilities of being. To guard the clearing is to maintain openness to those other possibilities within the dominion of enframing, to prevent enframing from becoming the sole manner of truth. This guardianship is not a refusal of technology. Heidegger is explicit: technology itself is not the problem, and enframing is itself a mode of being’s self-giving. The task of guardianship is not a return to the past but a thinking of the essence of technology, a questioning of from where enframing’s mode of clearing derives. That questioning is itself the manner of resistance to the forgetting of being.

5. Conclusions

The foregoing analysis calls for a brief summary of Heidegger’s critical transformation of Aquinas’s doctrine of divine illumination. Aquinas synthesizes the abstractive epistemology of Aristotle with the Augustinian tradition of illumination, constructing a comprehensive metaphysics of truth in which the soul’s participatio in the divine intellect, mediated through the illuminative activity of the agent intellect, serves as the structural foundation. Through this participation, the system roots the possibility of truth in the eternal archetypes, culminating in the theological guarantee of God as prima veritas. In its sustained interrogation of the metaphysical ground of cognitive activity and its tenacious pursuit of the transcendent dimension of truth, Aquinas’s doctrine of divine illumination achieves considerable theoretical depth, and it has long been regarded as the exemplary achievement of medieval theories of truth, occupying a position of considerable importance in the history of Western philosophy. With the rise in ontological phenomenology in the twentieth century, this mode of theological-transcendent grounding came under fundamental challenge.

Heidegger’s engagement with Aquinas’s doctrine of divine illumination takes the form of a dialectical sublation. On the one hand, he affirms the phenomenological insight that illumination names the structure of truth’s manifestation, and he acknowledges the theoretical necessity of pressing beyond propositional analysis toward the ontological ground of truth. On the other hand, he deconstructs the theological-transcendent foundation of the illumination doctrine, critiques its mode of grounding truth in an external and eternal transcendent being, and, through the core concepts of the clearing (Lichtung) and appropriation (Ereignis), re-establishes truth on an ontological basis. This sublation constitutes a creative transformation of the traditional theory of truth. The profound divergence between Heidegger and Aquinas on the question of truth-grounding derives in large measure from their opposing understandings of the temporality of being. For Aquinas, eternity is the paradigm of truth and time a deviation from it; for Heidegger, historicity is the fundamental character of truth and eternity merely an abstraction from, and forgetting of, time. Heidegger’s critique of the illumination doctrine differs from the simple negation characteristic of certain contemporary philosophical movements. Twentieth-century analytic philosophy has tended to dismiss traditional metaphysics as composed of pseudo-problems to be dissolved rather than resolved. Heidegger’s approach is more circumspect. He does not simply negate the illumination metaphor itself but strips away its theological casing and remakes it into the ontological concept of the clearing. He does not abandon the theoretical aspiration to grounding but reconceives its character. Traditional metaphysics grounds truth by ascending to a transcendent being that serves as its ultimate cause or archetype; Heidegger grounds truth by describing the existential-ontological structure of Dasein’s being-in-the-world within which disclosure occurs. The former asks: ‘What being grounds truth?’ The latter asks: ‘What structural conditions make truth possible?’ Heidegger’s answer to the second question is not the elimination of grounding but its existential reformulation: the clearing, as the domain of disclosure, constitutes a ground in the phenomenological sense precisely because no being or transcendent source prior to it is required for it. Whether this constitutes a philosophically robust form of grounding remains an open question, one the article acknowledges in the unresolved tensions noted in the conclusion.

It must be acknowledged, of course, that Aquinas’s doctrine of divine illumination, as a product of the medieval theological context, carries the limitations of its age. Its dependence on a transcendent being, its insistence on eternal archetypes, and its appeal to theological guarantees all reflect the specific understanding of being that prevailed in the medieval world. Yet this historical limitation is itself a disclosure of the situated character of truth. Aquinas’s theory is a faithful response to the medieval destining of being. Seen in this light, Heidegger’s critique does not aim to render Aquinas obsolete but to show that Aquinas’s truth, too, is historical and contextually situated. At the same time, Heidegger’s own ontological turn is not without its unresolved difficulties. If truth is historical and subject to forgetting, on what basis can a normative criterion of critique be established? If the clearing has no foundation, how is the threat of relativism to be resisted? In an age of technology, how is letting-be possible at all? These questions indicate that the shift from divine illumination to the clearing of being marks both the ending of a tradition of metaphysics and the opening of a new path of thought. Along that path, Aquinas’s theory retains its value as a partner in dialog by virtue of its commitment to the normative dimension, while Heidegger’s theory opens new possibilities by virtue of its disclosure of the historical dimension. The tension between them may well be the central issue that any contemporary theory of truth must take up and examine.