A Transcendental–Philosophical and Existential–Phenomenological Foundation of Sustainability on the Threshold of Theology

Abstract

This article explores the foundations and scope of theological discourse on sustainability by drawing upon transcendental–philosophical and existential–phenomenological perspectives. This study addresses the ongoing debate regarding the unique contribution and place of theological appeals to sustainability, especially in relation to secular arguments and audiences. Building on the structures of human cognition, freedom, and meaning, as well as the phenomenological concepts of givenness and promise, this paper critically examines how these structures can both motivate sustainable behavior and serve as interfaces to theological creation and eschatology. The methodological approach combines systematic philosophical analysis with affirmative theology, especially reflecting on the interrelation between the cognitive and experiential dimensions of human existence. The findings suggest that sustainability is not merely a moral option promoted by extrinsic or intrinsic motivators but is deeply rooted in the anthropological groundings of the human being. This study argues that a philosophically and anthropologically grounded discourse on sustainability serves as a vital interface between religious conviction and secular reasoning, extending the reach and impact of sustainability ethics.

1. Introduction

In 2015, the United Nations agreed upon 17 Sustainable Development Goals. With these goals (including poverty eradication, climate protection, peace, education, and equality), sustainability was articulated not merely as environmental policy but as a comprehensive ethical grammar for global coexistence encompassing political, economic, and social dimensions. The development of these goals was preceded by numerous earlier reflections and initiatives on sustainability. One example is the 1980 publication World Conservation Strategy: Living Resource Conservation for Sustainable Development. Its preface states that human beings, who aspire to economic development and wish to enjoy the riches of nature, must accept that the resources and capacities of the ecosystem are limited and must take into account the needs of future generations (cf. Sachs 2015, p. 5). Similarly, the Report of the World Commission on Environment and Development: Our Common Future—the so-called Brundtland Commission of 1987—states that sustainable development seeks to meet the goals and aspirations of the present without jeopardizing those of the future. Beyond these secular formulations, which seek to raise human awareness for sustainability and to stimulate corresponding courses of action, there is no shortage of contributions from theology that support these impulses from the perspective of the concept of creation and theological ethics (cf. for example Abubakar 2024).

The debates on sustainability are marked by a growing awareness that technical solutions and political agreements alone are insufficient to address the ecological and social crises of the present. While appeals to sustainable behavior is often grounded in terms of limitation of resources or intergenerational justice, its deeper anthropological and existential foundations remain to a wide extent underexplored. In particular, the question of why sustainability should appear as a binding demand rather than as a contingent ethical preference continues to require further conceptual clarification.

This article argues that sustainability can be understood only if it is grounded not merely in extrinsic norms and moral add-ons imposed upon otherwise autonomous subjects, but in the horizon structure of human existence in general. Following this aim the article argues on a transcendental–philosophical and existential–phenomenological basis. The underlying understanding of self-transcendence encompasses the ethical intensification of embodied and vulnerable exposure to others and to the natural world, and to temporal finitude. It must not be misunderstood as a movement away from embodiment or materiality or even as an expression of an extended radius of dominion over nature. Human agency, understood as self-transcending, is necessarily exposed to temporal irreversibility, embodied dependence, and relational entanglement.

In this article philosophy and theology are approached as distinct yet interacting discursive practices: Transcendental philosophy serves to articulate the conditions of possibility under which sustainability becomes intelligible as a meaningful ethical demand, while existential phenomenology elucidates how this demand is concretely and existentially experienced. Theology, in turn, is introduced as a faith-based hermeneutical horizon that interprets these conditions, without overriding their philosophical autonomy. In a general sense: Theology is not understood as an epistemically superior framework to theology, but as an optional horizon with an invitational character.

The originality of this contribution thus consists of demonstrating that sustainability appears as an existential demand arising from the horizon structure of human existence and the resulting responsible action. Moreover, it will be shown that it is exactly this structure which opens the field for a contemporary theological interpretation in the sense of relational, embodied and responsible stewardship.

This article is deliberately restrained in claims of universality: it does not prescribe a normative blueprint applicable across contexts, but articulates the shared vulnerability of embodied beings exposed to finitude and irreversible consequences. Such a conception of universality resists instrumentalization precisely by refusing closure and totalization.

Finally, the argument situates itself within a post-metaphysical and post-Gödelian horizon of critical reason. Within this horizon, the dialogue with contemporary theologies of creation—particularly relational and ecological approaches—serves to illuminate how philosophical insights into freedom and responsibility can resonate with theological interpretations of creation as an ongoing, relational event.

2. Transcendental–Philosophical Foundation of Sustainability Based on the Human Structure of Transcendence (Karl Rahner) and the Experience of Freedom (Hermann Krings, Thomas Pröpper)

Transcendental philosophy inquires into the conditions of possibility for acts of cognition. In the origins of transcendental philosophy, Immanuel Kant refers to these conditions of possibility as transcendental because they cannot be derived empirically; rather, they are beyond empirical, sensory possibilities of cognition (cf. Kant [1781] 2014, p. B25).

In the light of the modern philosophical trajectory that has often interpreted self-transcendence as the expansion of subjective mastery over nature, this concept requires careful qualification. Therefore, in a contemporary context, the understanding of transcendentality must be critically reexamined and characterized as open-ended and revisable—which we will especially pursue for the application of transcendentality to sustainable behavior later. The self-transcendence at stake here must not be confused with the Cartesian project of becoming “masters and owners of nature,” nor with an instrumental rationality rooted in the mathematization of nature characteristic of early modern science. Rather than implying control or sovereignty, self-transcendence here names the exposure of finite freedom to conditions it neither fully comprehends nor commands. This interpretation does not deny the critical achievement of Kantian autonomy, but reinterprets it under conditions of ecological vulnerability and the irreversible impact of human action.

Karl Rahner is credited with the achievement of having translated Kant’s reflections on transcendental conditions of knowledge into a theological context, in relation to the human capacity to be addressed by a revelation from God. For Rahner, the human ability to ask transcendental questions arises from their structure of transcendence (cf. Rahner [1976] 1999, pp. 26–27): in order to ask questions that go beyond oneself, the human being must be a being of transcendence, capable of exceeding the empirically perceptible. According to Rahner, in this capacity to question himself and his cognitive capabilities, not only does the infinite horizon become manifest, but conversely, the infinite horizon also proves to be the very condition that makes such questioning possible. Human beings experience themselves in the tension between infinity and finitude, and it is precisely in reaching beyond the boundaries of the finite that one comes to experience and recognize one’s own finitude. The human capacity to ask questions beyond empirical knowledge opens up, from a theological perspective, the horizon for the question of God. Rahner concludes that God’s free revelation must find in human beings a recipient who is also capable of receiving this revelation: God does not only communicate himself, but his self-communication is furthermore an affirmation about the quality of humanity itself (cf. Rahner 1967, p. 375).

Rahner refers to this openness of human beings to revelation as the “supernatural existential.” In accordance with God’s will for salvation, the human being is, a priori, oriented toward God’s revelation. Therefore, humans are, in principle, capable of accepting the revelation attested to in the Bible. Rahner seeks to demonstrate the conditions of possibility for this acceptance (cf. Cichon-Brandmaier 2008, pp. 36–37).

If this transcendental theology shall be made fruitful as a hinge with secular philosophical discourses however, one should be cautious about inserting the idea of God as philosophically necessary as Rahner seems to do. Accordingly, in later transcendental–philosophical and theological discourses, Rahner’s approach has also been critically received. It is objected that Rahner infers the real existence of God from the fact that human beings are oriented toward a possible God: for Rahner, God as the aim (the “Woraufhin”) of human questioning is at the same time its real, existing ground. This raises the question of whether and to what extent a theology that argues transcendental–philosophically is permitted to go beyond the boundaries set by critical reason. As Klaus P. Fischer puts it: there is good reason to doubt “whether the biblical exhortation to humankind to become ‘hearers of the Word’ (of God) can be demonstrated to be philosophically necessary, as Rahner tried to do.” (Fischer 1991, p. 19). Similarly, Thomas Pröpper criticizes Rahner’s concept of humans as “hearers of the word” insofar as seemingly, by philosophical reasoning Rahner lifts an implicit knowledge about God to an explicit recognition (cf. Pröpper 2011, p. 405). Furthermore, later transcendental–theological approaches as Thomas Pröpper’s criticize Rahner’s understanding of the free act of human existence and the reaching out toward God’s free self-revelation, inasmuch as it neglects the transcendental unconditionality of the human act of freedom itself—or seeks to ground it only a posteriori in reference to God.

Hermann Krings and Thomas Pröpper further develop Rahner’s transcendental approach in a strictly transcendental–philosophical and freedom–theoretical manner. The possibility of an affirmative inference of God is demonstrated, without claiming a necessity beyond the limits of critical reason. As we will see, the concept of sustainability also corresponds to the horizon structure which will be provided by freedom–theoretical reflections.

In the transcendental theology further developed especially by Hermann Krings and Thomas Pröpper, the human being is described as a being characterized by the dialectic of formally unconditional yet materially conditioned freedom (cf. Krings 1980, pp. 40–68).

Without this structure of our freedom as formally unconditional, basic acts of communication would not be possible. To love another person is not satisfied with the conditionality and finitude of this love, but rather grounds itself in its formal unconditionality, which points beyond empirical reality. According to Gabriel Marcel, to love a person means as much as to say: “but you will not die” (Marcel 1961, p. 79).

This pointing beyond empirical reality applies to every act of communication as well: every form of communication contains—even if only in a negated manner—a form of affirmation of the other. Yet, this affirmation can only find support in a “yes” that points beyond empirical reality. Parents who bring a child into the world implicitly presuppose that their own “yes” to the child exceeds the limits of their own experiential reality and is embedded in a larger, more comprehensive “yes.” Conversely, their “yes” to the child would become obsolete if, within the foreseeable scope of their own lives, limits to its realization were set. This would be the case, for example, if a comet impact that would destroy the Earth were imminent, and therefore the parents’ “yes” to the child were overridden by a global “no.”

Stated generally: the free self intends the unconditional recognition of the freedom of the other. As Hermann Krings writes: “Ultimately and primarily freedom gives itself content by affirming other freedom. Only in the decision for other freedom does freedom manifest itself in its full form” (Krings 1980, p. 174). Krings concludes that, from this consequence of freedom—the affirmation of the freedom of others—“a fundamental aspect or basic character of any self-determination of the will” (Krings 1980, p. 174) arises. Pröpper argues along the same lines: “Only in the affirmation of other freedom is the unconditional character of one’s own freedom established as such; only here is the unconditionality of opening oneself and determining oneself not just implicitly carried out but explicitly manifested and made truly apparent” (Pröpper 2011, p. 641).

This reaching out of freedom toward the other free self can only realize the intended freedom of the other to a limited extent. Every act of materially freedom involves a striving toward its formally unconditional form. The materially conditioned freedom of the human being is dependent on its affirmation and enabling beyond the horizon of one’s own lifeworld.

Thus, every act of materially conditioned freedom can be interpreted as a longing for a situation in which there are no limits to the striving of freedom for its formally unconditional form. In other words, human beings, because of their experienced freedom, transcend themselves toward the other–which can be the other person or the absolute Other–and in reaching out to the other’s freedom, they find its transcendental enablement.

If sustainability means that resources are only taken from the Earth’s habitat to the extent of its own capacity for regeneration, then the foundation is laid for a relationship between free and responsible agents both within and beyond the horizon of one’s own life. Here too, it holds true: no limits can be set to the striving of freedom for its formally unconditional form without contradicting its structure of transcendence. In other words: a foreseeable rupture in the continuity of the habitat as the space of life and as the bearer of experiences of freedom would interrupt the horizon structure of freedom and deprive it of its very transcendental grounds of possibility.

In a post-Gödelian context of critical reason, we can extend the transcendental grounding of sustainability in so far, as the orientation toward the infinite and the capacity to think beyond oneself encompasses the embodied and vulnerable self-exposure to others. Conversely, this means: in order to recognize the necessity of sustainability in theory and practice, human beings must, by their structure of transcendence and embodied vulnerable self-exposure, be oriented toward what lies beyond, and thus remain ultimately open toward the infinite. In caring for creation, human beings recognize their own capacity to transcend themselves; they do not live for themselves alone. The “sustainable” is thus the ethical expression of this transcendental structure: human beings experience themselves as finite and vulnerable, yet responsible beings in history and come to realize that their actions have consequences that go beyond their own spatial and temporal borders.

3. Existential-Philosophical and Phenomenological Foundation of Sustainability Based on the Promise Structure of Givenness (Jean-Yves Lacoste) and the Question of Meaning (Maurice Blondel, Jean-Paul Sartre, Volker Gerhardt)

While the transcendental analysis primarily clarifies the conditions under which sustainable behavior and responsibility for the future becomes intelligible and related to free decisions and actions, phenomenology addresses how this responsibility is existentially experienced and encountered prior to intelligible reflections and moral deliberation.

Among the givens of human life and its existential preconditions is the experience of existence as meaningful, or at least the need for meaning—even if this need may be factually denied; at the same time, the question of meaning also intersects with transcendental, intelligible concerns, since it is not only existentially given but also a matter of human reflection.

Opening the space of meaning can be regarded as an essential precondition for sustainable behavior: Maintaining the capacity to ask the question of meaning makes a decisive difference to human existence insofar as it prevents agency from being reduced to mere functionality or short-term utility, to what is immediately effective, profitable, or controllable. The suppression of the question of meaning fosters forms of life oriented toward consumption, optimization, and acceleration. If this is the case, human action becomes increasingly indifferent to long-term consequences. Sustainability, however, presupposes exactly the opposite: namely the ability to act for reasons that exceed immediate benefit, present interests, or calculable outcomes. The openness of the space of meaning enables to recognize values that are not exhausted by utility—such as practices of care and responsibility for future generations, the intrinsic worth of non-human life, or the preservation of conditions that sustain life beyond one’s own lifespan.

One approach to the quest for meaning is outlined by the Christian philosopher Maurice Blondel in his groundbreaking work “L’Action”. In this work, he highlights action as the fundamental phenomenon of human life (cf. Blondel [1893] 1993). According to Blondel’s core argument, human action must always be bound to an infinite capacity and to a dimension of meaning that transcends the human person. Thus, rational human action can never be limited, but always holds an openness toward the infinite and toward an ultimate meaning to which every act ultimately refers.

For the existentialist Jean-Paul Sartre, however, the question of meaning is a meaningless question. According to Sartre, only the hope finding something makes the search possible; if one already knows that one will not find anything, the question becomes useless, senseless, and without foundation. Yet, since humans cannot stop themselves from asking this question, they live in a tension between totality and fragmentariness. This tension makes them impossible beings, a flawed construction. They indulge in a useless passion (cf. Sartre 1949, p. 708) because they seek something they can never attain. Ultimately, the deepest expectation of human beings remains unfulfilled; they must acknowledge that they live in an absurd world.

It is precisely such negations of the existence of meaning that the contemporary philosopher Volker Gerhardt paradoxically sees as a reaching out toward meaning (Sinn). Even if the question of meaning were denied or even forbidden, according to Gerhardt, both the denial and the prohibition would themselves pursue a kind of meaning (cf. Gerhardt 2017, p. 22). Even in the question itself, Gerhardt argues, meaning is articulated, as it distinguishes a question as a question. In this way, the dimension of meaning that lies – at least implicitly – behind every question of meaning proves to be a constitutive element in every relationship between subject and world (cf. Gerhardt 2017, p. 23)–an argumentation which we also find in Merleau-Ponty, who describes meaning as a constitutive way of being to the world (cf. Merleau-Ponty [1945] 1952, pp. 503–4). Gerhardt argues that the expectation of a positive fulfillment of meaning does not necessarily have to be related to a meaning that transcends the reality of one’s life. The expectation of meaning can remain limited to a specific task or to one’s own life. Nevertheless, Gerhardt admits that there are good reasons to ascribe to all expectations of meaning a fundamental meaning. This would grant these expectations a status independent of all internal and external conditions. In this fundamental meaning, Gerhardt sees a point of connection between the question of meaning and the divine (Gerhardt 2017, p. 24).

We can conclude: Even if, according to Gerhardt, the question of meaning can remain limited to one’s own foreseeable life domain, the open question of the possibility of a fulfillment of meaning that goes beyond one’s own life can never be definitively settled. If a person holds on to this possibility and to the question of meaning that points beyond one’s own life—if not to a fulfilled expectation of meaning—they cannot disregard the need to contribute, at least, to maintaining a continuum of conditions that make it possible to pose this question of meaning in the first place. In order not to fall into a self-contradiction with their own orientation toward the question of meaning, humans cannot consciously allow the future continuation of their lifeworld as the bearer of the question of meaning to become foreseeably cut off by the unsustainable depletion of resources. Here too, the following holds: The question of meaning—or, at the very least, the question of the meaning of meaning—will always be a part of what it means to be human. It cannot be restricted to one limited horizon of life and time, but instead demands integration into a collective dynamic that transcends both time and space.

Next to the reflections about the quest for meaning, on a phenomenological level, also the concepts of being exposed to the Other prove to be particularly relevant for a discourse on sustainability. A fundamental given of human existence is articulated by Emmanuel Levinas in terms of responsibility and the encounter with the Other. Although Levinas does not develop this insight in explicitly ecological terms, but rather within an intersubjective framework, his thought nevertheless entails a decisive shift away from metaphysical and ontological determinations of the human being. Instead of defining the human through being, essence, or totality, Levinas emphasizes vulnerability and responsibility as constitutive features of subjectivity. For Levinas, the task is to articulate a relation to being beyond totality—a totality that seeks to absorb or erase alterity. Human existence is thus situated within a movement, a desire directed toward the Other: toward otherness itself and toward the exteriority that resists conceptual assimilation (Levinas [1961] 1984, p. 4).

In Maurice Merleau-Ponty’s phenomenology, embodiment constitutes a fundamental condition of human existence. The body mediates both world-relation and self-relation, thereby challenging the dualistic separation of nature as pure exteriority and consciousness as pure interiority. For Merleau-Ponty, the body is not something one possesses but something one is (Merleau-Ponty [1945] 1952, p. VII). Accordingly, the body of the other must be understood not as a neutral object, but as the expression of the other’s presence. Embodiment thus establishes a field of meaning in which self, other, and world are intrinsically intertwined, grounding relationality, vulnerability, and responsibility as constitutive features of human existence.

Also, the concepts of gift, giving, and self-givenness have gained particular importance in the phenomenological discourse and cannot be neglected in a discourse about sustainability. Following the foundation of phenomenology by Edmund Husserl in the early 20th century—which brought the-givenness of phenomena into focus, that is, the endeavor to “question things in their self-givenness and to set aside all extraneous prejudices” (Husserl [1913] 1976, p. 41)—the theme of the gift has been further developed, especially in contemporary French phenomenology. Jean-Luc Marion, in particular, has made a significant contribution to the further development of the phenomenology of the gift, whereby Marion, in the sense of a radical redefinition, uses the method of reduction to lead back to pure givenness as a phenomenon that gives itself (cf. Marion [1997] 2013).

The phenomenologist Jean-Yves Lacoste, in his phenomenological studies of the gift, focuses less on an epistemological radicalization of the gift, and more on the affective presence (gift as something that affects, that presents itself to the senses) as well as the promissory structure of the self-giving phenomenon. With the latter, Lacoste safeguards the gift and what is given from various dangers: the gift, for example, is always at risk of becoming property and thereby losing its character that makes it a gift (cf. Lacoste 2008, p. 170). The gift therefore always moves within a fragile space between the self and the other. It also runs the risk of remaining tied to a present experience, and thus being perceived only partially and in a limited way, deprived of its further flow in time and between givers and recipients. What is given—including in connection with the being that gives itself, and especially in relation to personal self-giving—according to Lacoste, is dependent on never being the final given, in order not to solidify into a rigid present or become a closed fact. (cf. Lacoste 2008, p. 172; Lacoste 2011, p. 325). In our case of sustainability, this applies especially to the givenness of existence, life, nature, the Earth’s habitat and the cosmic boundary conditions which make life on Earth possible.

Lacoste addresses this risk associated with the gift and what is given by introducing the category of promise, which he sees as inherent in every act of self-givenness. In developing this category, Lacoste draws inspiration from Martin Heidegger’s existential concepts of being-with (Mit-sein) and care (Sorge) (cf. especially Heidegger [1927] 1979, pp. 121–124). According to Lacoste, these concepts are expressed in every act of giving: for example, in the giving of alms, not only is something external given but to some extent, the persons giving always give something of themselves. They enter into a relationship with the recipient and express their being-with and their care. In order for this relationship not to break off abruptly, it must always be linked to the category of promise (Lacoste 2008, p. 172). This category therefore opens a horizon which encompasses every givenness and every self-giving appearance (Lacoste 2008, p. 166).

If the dimension of promise were taken away from that which gives itself, this would consequently mean the end of experience and the end of time. Similarly to Husserl’s investigation of perception, which is animated by continuity with the past and the anticipatory reaching out toward what is to come (Husserl 1939, p. 118), or Maurice Merleau-Ponty’s observation that a melody is not merely a sum of notes but can only be understood in its entirety (Merleau-Ponty [1948] 1996, p. 62), Lacoste uses the example of music to illustrate the character of promise inherent in what is given: While listening for example to a prelude by Johann Sebastian Bach, the bars of the piece that have already been listened to promise further auditory experience, whereas an unfinished and abruptly interrupted work would break the promise inherent in it. Lacoste argues similarly with the example of spoken words in a conversation: Without the dimension of promise, a conversation could never be relied on to find an appropriate and satisfactory conclusion. Correspondingly, language itself could only describe what is closed and factual, but could never convey self-giving presence (cf. Lacoste 2008, pp. 172–74).

Transferred to the context of sustainability, this would mean: through sustainable behavior, human beings respond both to their own phenomenality as oriented towards otherness, as vulnerable, and to the phenomenon of the world as given and self-giving. The givenness of the world and of human beings cannot be limited or isolated spatially and temporally, but instead, as Lacoste has shown, points beyond itself in the dimension of promise. Without keeping this dimension open, everything that exists would solidify into mere fact and lose its structure of givenness—and therefore its anticipatory reach. In Lacoste’s words, a world depleted of its resources would be a broken promise that undermines the structure of givenness of both humanity and the world.

4. Theological Interpretation of Creation and Eschatological Completion as a Fulfillment of the Transcendental-Phenomenological Foundation of Sustainability

Interpreting the horizon structure of fundamental human conditions that has been outlined—such as the transcendental structure of human questioning, the experience of freedom, the self- and world-interpretation as gift and givenness, the experience of self-exposure and vulnerability, as well as the quest for meaning—and filling it in an affirmative and confessional way is the task of theology. Theology does this through faith in the absolutely free God, who has created in human beings a free counterpart and has entrusted to them a habitat for themselves and their fellow creatures (creatio prima). As the image of God, humans step into the role of the Creator as stewards of creation and bear responsibility for safeguarding the entrusted habitat.

Any theological appropriation of sustainability that invokes the concept of imago Dei must reckon with the ambivalent history of this notion and make sure that it is not understood as an ontological marker of superiority or dominion. The idea of humanity as the image of God has more than once been instrumentalized to justify hierarchical ontologies, patriarchal structures, and the exploitation of non-human nature. Such uses of creational doctrine have often relied on implicit metaphysical gradations that position the human subject above creation as its sovereign interpreter or master. Therefore, contemporary theological interpretations increasingly emphasize its relational and dynamic character (cf. for example Moltmann 1985). To be created in the image of God in this sense is a mode of existence characterized by responsibility, responsiveness, and relationality within creation. It does not signify a distance from materiality, but instead a deeper involvement and entanglement in it. Human beings bear the image of God precisely insofar as they are exposed to vulnerability, dependency, and the ethical demands arising from the common creatureliness. This interpretation resists anthropocentric and exploitative readings by situating human dignity within the community of creation, not above (cf. McFague [1993] 2000; Deane-Drummond 2014).

Such a relational understanding of the imago Dei also aligns with ecological theologies that emphasize interconnectedness and care. It reframes human agency not as dominion over nature, but as a particular form of responsibility for the conditions of life. In this sense, the imago Dei does not legitimate unsustainable practices, but provides a critical theological resource for articulating sustainability as an expression of faithful relationality within creation. Lexically—and with biblical justification (Genesis 1:28)—the ecological interpretations can be illuminated through the range of meanings of the Hebrew terms radah (which also denotes the shepherd’s attentive roaming with the flock for its well-being) and the more militant kabash, which can also mean the sovereign subduing of the rearing, anti-creational chaos (Zenger 1983, pp. 90–96)–thus rendering a contribution to God’s creational act.

The transcendental and phenomenological horizon structure outlined above finds, from a Christian affirmative perspective, its ultimate theological grounding not only in reference to a primordial creation, but also in relation to the ongoing creation (creatio continua)—in other words, the concept of God’ incessant act of preserving creation in existence (cf. Swinburne 1994, p. 128; Astley 2000, pp. 15–16; Astley 2016, pp. 89–92). Biblically this aspect can be grounded with references to Psalm 104 or texts of the wisdom tradition like Sir. 16:24–17:14. These texts can be interpreted as an appeal to respect the heartbeat of nature–in the sense of sustainability: respect for its regenerative rhythm–instead of forcing upon nature the rhythms of human economy and utility (cf. Huber 2021, pp. 274–76, 388–95). It is precisely this reference to ongoing creation that theologically guarantees that human efforts to preserve creation, as well as the autonomy of nature, are not limited to what is immanent, but instead remain open to interaction with divine action, and ultimately to possible fulfillment by God. A practice of sustainability is thus participatory affirmation of this divine preservation. Not least through this continual call to humankind, nature as creation becomes the place of God’s unceasing address to humanity. To use Rahner’s words, human beings live as “hearers of the word” even in the history of matter, and in doing so profess that creation is not merely external material to be used and consumed by humans, but rather—although in varying degrees—a medium of divine self-communication.

Finally, Christian hope points toward the completion and renewal of creation at the end of times (creatio nova). The relationship between the old and the new remains largely open and indeterminate in eschatology. However, within the framework of eschatology and the theology of creation, sustainability can be seen as appropriate behavior and as the human contribution to ensuring that the history of the Earth and the cosmos does not end in nothingness, but rather that the possibility of their fulfillment remains open—or, in other words, that the possibility of linking a history of fulfillment to earthly history is not interrupted. In this way, sustainability becomes an eschatological category within immanence: through sustainable action, human beings anticipate eschatological fulfillment by taking seriously the continuity of creation as a bridge to God’s perfecting action and by contributing to its continuation through their sense of responsibility.

5. Results

The central result of this study is the reconceptualization of sustainability as a structural implication of human transcendent structure and existential experience rather than as an externally imposed moral obligation or technocratic norm. By bringing transcendental–philosophical and existential–phenomenological approaches into dialogue, the analysis has shown that sustainability emerges from the very conditions under which responsible agency becomes possible.

From a transcendental perspective, human freedom is necessarily oriented beyond itself. As self-transcending, freedom is exposed to temporal irreversibility, relational interdependence, and the vulnerability of embodied existence. Actions are never confined to the present moment alone but inevitably shape future possibilities, often in ways that cannot be fully anticipated or reversed. Importantly, the concept of self-transcendence employed here does not entail a denigration of materiality or embodiment. On the contrary, self-transcendence has been shown to denote an ethical intensification of embodied relationality. Responsibility for the future is inseparable from attentiveness to the material conditions of life, including the human body and the natural world. Sustainability, in this sense, concerns not an escape from material existence, but a deeper acknowledgment of dependence upon it.

Phenomenologically, responsibility for future consequences is experienced as something that addresses the agent prior to reflections on intelligibility or moral deliberation. An intact, unexploited nature—phenomenologically understood as givenness that points beyond itself—is at the same time the bearer of a continuity of the experience of freedom, the experience of being exposed to the other, as well as the question of meaning, that extends beyond individual earthly existence. This experiential dimension helps explain why sustainability can exert binding force without relying on moralization or coercion, it appears not as an optional ethical supplement to otherwise neutral action: it is lived as a response to the experience of freedom and quest for meaning, embodiment and vulnerability rather than as compliance with a rule. Nature therefore is not something external to the human being. Rather, basic anthropological structures necessarily lead to an ethical imperative that calls for treating the world as something inherent in, and participating in, the very essence of being human.

From this, the following conclusions can be drawn for a theological discourse on sustainability:

• A theologically based discourse on sustainability that makes use of philosophical approaches as outlined above, respects the autonomy of philosophical approaches. However, by incorporating philosophical insights theology preserves its self-reflective character as well as its access to a secular discourse. The philosophical results outlined here resonate with contemporary theological articulations of ecological responsibility, most notably Pope Francis’ encyclical Laudato Si’. While Laudato Si’ does not function as a normative foundation for the present argument, it exemplifies how ecological sustainability can be framed as an anthropological and relational concern rather than as a merely technical or economic problem. Its emphasis on interconnectedness, vulnerability, and responsibility for future generations corresponds closely to the philosophical account of freedom and responsibility developed here. In particular, Laudato Si’ articulates a vision of human agency that is neither sovereign nor self-enclosed, but fundamentally relational and situated within a shared, fragile world. This theological resonance underscores the broader significance of the philosophical result: sustainability becomes intelligible as a response to the fragility of creation and human coexistence. The convergence between philosophical analysis and theological interpretation thus highlights the potential of sustainability to function as a shared horizon of responsibility across secular and religious discourses.
• A further result of the analysis concerns the critical reconfiguration of a universality often implied in theological discourses (often with regard to the concept of imago dei). Considering well-established critiques of universalizing philosophical frameworks—particularly their historical instrumentalization in contexts of colonial domination, exploitation, and ecological destruction—the universality implied in this account has been deliberately reformulated. It does not consist in a comprehensive normative blueprint or a decontextualized metanarrative, but in a minimal and negative universality grounded in shared vulnerability, finitude, and exposure to irreversible consequences. This form of universality resists domination precisely by refusing closure and totalization.
• Precisely through this self-reflexivity as well as through its own perspective and method as a faith-based discipline, theology makes an indispensable contribution to the societal discourse on sustainability and fills a vacuum that would otherwise remain. Through a serious connection to purely secular discourse, theology does not merely reveal conceptual options for possible affirmative affirmations—such as the concept of God as the bearer of absolute freedom or absolute meaning—as ultimate foundations of sustainable behavior. More than that, theology, with a confessional grounding of sustainable behavior embedded in both ecclesial and personal religiosity, can illustrate a way and quality of existential appropriation of secular-philosophical considerations on sustainability that would remain inaccessible to purely secular perspectives without the voice of theology.

Taken together, these results demonstrate that sustainability can be understood as a constitutive dimension of responsible human existence which open the field of theological interpretation. Rather than relying on moral exhortation or technocratic optimization, the proposed perspective grounds sustainability in the structure of human existence itself, while remaining critically reflexive, context-sensitive, and open-ended. This reconceptualization offers a robust philosophical and theological basis for further interdisciplinary dialogue on sustainability, without reproducing the pitfalls of domination, abstraction, or dualistic denigration of material life.