I. Introduction: Basel, Conciliar Crisis, and the Problem of Ecclesial Visibility

When Nicholas of Cusa arrived at the Council of Basel in 1432, he entered what would become the most ambitious – and ultimately the most divisive – ecclesiastical experiment of the fifteenth century. Convened to secure reform and unity after the Great Schism, the council soon turned into a protracted struggle over the locus of authority in the Church. Between 1432 and 1437, its sessions oscillated between genuine attempts at institutional renewal and increasingly hardened confrontations with Pope Eugenius IV. The break of 1437, when Cardinal Julianus Cesarini and several delegates – including the young canon lawyer Cusanus – left Basel to support the papal position, marked not only a constitutional fracture but also the collapse of a shared imagination of ecclesial unity.

Basel has long been described in historiography as the last dramatic outburst of medieval conciliarism. Yet recent studies have shown that the council’s inner conflicts did not simply oppose “council” to “pope,” but unfolded along multiple juridical, institutional, and theological fault lines; they reflected deeper transformations characteristic of late medieval political and intellectual life: the competition between universal and territorial powers; the instability of the Dionysian hierarchical paradigm; the growing influence of nominalist critiques of universals; and the emergence of new legal, political, and institutional configurations that no longer fit inherited models of divine–ecclesial order.Footnote ¹

For Nicholas of Cusa, Basel was the formative crucible of his early career. The years 1432–1437 witnessed his evolution from diocesan advocate in the Trier dispute, to conciliar speaker and negotiator, to papal envoy in the delicate missions to the Hussites and later to the Byzantine court. His De concordantia catholica (1433), composed within this turbulent environment, is therefore not a detached speculative treatise but a manual written in actu – in the midst of conciliar practice. It registers contemporary arguments, surveys canonical and patristic traditions, and seeks a method for mediating divergent theological and political claims into concord.

After his departure in 1437, however, Cusanus never again produced a treatise explicitly devoted to conciliar structures. Traditional scholarship has often interpreted this silence as proof of a decisive “turn”: from conciliar jurist to papal loyalist, from constitutional theory to speculative metaphysics. The contrast between the institutional detail of De concordantia catholica and the metaphysical architecture of De docta ignorantia (1440) and De coniecturis (1442–1444) has reinforced the image of discontinuity.

This article challenges that interpretation. It argues that Cusanus’s speculative writings of the 1440s should be read as a continuation and transformation of the problem he first confronted at Basel: how the Church can be seen as one body amid divergent authorities, practices, and perspectives? Far from abandoning ecclesiology, Cusanus relocates it. He reframes the failed conciliar debates within a broader reflection on the conditions under which ecclesial unity can appear – historically, sacramentally, and intellectually.

A key witness to this shift is the 1442 letter to Rodrigo Sánchez de Arévalo, where Cusanus speaks of the Church as an ecclesia coniecturalis: a Church visible only through signs, conjectures, and finite historical forms.Footnote ² Although the letter is not a systematic ecclesiological treatise, it constitutes a situational intervention in which Cusanus explicitly brings the insights of De docta ignorantia and De coniecturis to bear on an unresolved ecclesio-political conflict.

This phrase signals not withdrawal from the ecclesial crisis, but a new attempt to understand why ecclesial unity cannot be secured by juridical arrangements alone. The failure of Basel revealed the limits of an imagination that sought concord through fixed structures rather than through interpretive practices capable of mediating difference.

The two major speculative works that follow – De docta ignorantia and De coniecturis – must therefore be read against this background. De docta ignorantia reframes the conciliar tension between divine order and human arrangement as a universal epistemic principle: all finite knowledge proceeds through comparative measures that never coincide with the infinite measure of God. De coniecturis, written immediately thereafter and addressed once more to Cesarini, develops a practical ars coniecturalis – an “art of conjecture” – that describes how unity and plurality can coexist in concrete life, doctrine, and institutional practice.

Taken together, these works amount to a speculative continuation of conciliar reform. They shift the debate from who decides (pope or council) to from where the Church can be perceived as Church. Cusanus no longer searches for constitutional solutions but for hermeneutical ones: ways of discerning the unity of Christ’s mystical body within the plurality of historical expressions, viewpoints, and rules. Basel becomes for him not only a political failure but also the starting point of a deeper investigation into the visibility of the Church in an age of emerging plurality.

This article operates on three analytical levels. First, it offers a historical reconstruction of Nicholas of Cusa’s involvement in the Council of Basel and the ecclesio-political conflicts that shaped his early writings. Second, it advances an interpretive reading of Cusanus’s speculative works as historically situated responses to that conciliar impasse, attentive to genre, audience, and immediate context. Third, it proposes a conceptual synthesis that seeks to clarify the ecclesiological implications of Cusanus’s notion of the ecclesia coniecturalis. While this final level necessarily involves analytical extrapolation, it remains grounded in the historical and textual analyses developed in the preceding sections.

II. The Council of Basel: Authority, Reform, and Political Pressure

The Council of Basel was convened in 1431 in the wake of the Great Schism and in continuity with the conciliar reforms initiated at Constance.Footnote ³ Its stated aims were ambitious yet traditional: the restoration of ecclesial unity, the reform of abuses in church governance, and the clarification of authority within the Church. At stake was not merely a procedural question but the unresolved problem of where ultimate ecclesial authority resided – whether in the pope as singular head or in the council as the representative body of the Church.

From the outset, these theological and canonical debates unfolded within a charged political landscape. Reform-minded conciliarists increasingly sought to compel papal compliance by juridical and procedural means that stretched established norms, including the appeal to Haec sancta as a standing principle of conciliar supremacy and the strategic use of coercive decrees. Pope Eugenius IV, for his part, responded by attempting to dissolve or relocate the council, thereby reasserting papal prerogatives through acts of administrative authority. What emerged was not a balanced process of reform, but an escalating contest in which both parties sought decisive victory.

The reforming impulse that animated conciliarism did not arise in isolation. It drew on late medieval political theories that limited monarchical authority in favor of corporate and representative structures, most notably in the work of Marsilius of Padua, whose Defensor pacis articulated a vision of communal governance that resonated far beyond strictly political discourse. At the same time, new spiritual movements associated with the rise of urban culture – such as the Devotio Moderna – fostered forms of religious life that emphasized interior reform, communal discipline, and practical piety, reinforcing the conviction that ecclesial renewal required structural as well as spiritual transformation.Footnote ⁴

It is from a medieval perspective of ordered concord that Basel can be said to have failed. The council proved unable to stabilize a shared framework in which ecclesial authority could function as a clear and reliable interlocutor for secular rulers. Neither pope nor council succeeded in embodying the Church’s unity in a manner that could command durable political recognition. In this respect, Basel unintentionally contributed to the erosion of the late medieval Church–state synthesis and exposed the difficulty of defining the Church’s place within an increasingly plural and politically differentiated order. This unresolved tension forms the immediate historical horizon of Cusanus’s conciliar engagement.

III. Interpreting Cusanus at Basel

The difficulty of situating Nicholas of Cusa within the conciliar conflicts of the 1430s has shaped modern interpretations of both his thought and the Council of Basel itself. How one reads Cusanus’s role at Basel – whether as a committed conciliarist, a cautious mediator, or a papal loyalist in formation – has become a touchstone for broader assessments of the conciliar experiment and its legacy. The historiographical debates surrounding Cusanus thus mirror the structural ambiguity of Basel: an assembly caught between reform and rupture, between constitutional imagination and political impasse.

Within the history of conciliarism, as developed in the influential works of Brian Tierney, Francis Oakley, and Antony Black, Basel has often been framed as the culmination of medieval constitutional theories that sought to limit papal authority by grounding ecclesial power in the corporate whole.Footnote ⁵ More recent studies by Johannes Helmrath, Jörg Dendorfer, John B. Morrall, and others have emphasized how deeply the council’s debates were embedded in the political, legal, and diplomatic realities of the fifteenth-century empire.Footnote ⁶ Within this historiography, Nicholas of Cusa typically appears as an early sympathizer of conciliar reform whose departure from Basel in 1437 marks a decisive shift toward papal centralism.

A second body of scholarship – primarily philosophical and theological in orientation – has approached Cusanus from a different angle. Scholars, such as William Hoye, Thomas Leinkauf, Clyde Lee-Miller, Johannes Hoff, and David Albertson, have focused on his contributions to negative theology, epistemology, and metaphysics.Footnote ⁷ In this tradition, De concordantia catholica is often treated as a largely isolated early work, standing in tension with the speculative architecture of De docta ignorantia and the complex semantics of De coniecturis.

Despite their differences, both historiographical strands tend to presuppose a sharp rupture in Cusanus’s development: the young conciliar jurist versus the mature speculative theologian. Although scholars such as Jovino Miroy and Lawrence Bond have questioned this dichotomy, their attempts at integration have remained partial.Footnote ⁸ Conciliar historians rarely engage the speculative writings in detail. In contrast, intellectual historians seldom embed those writings within the concrete crises of Basel, the Hussite negotiations, or the diplomatic tensions of the early 1440s.

A further dimension emerges from the work of Michel de Certeau and Henri de Lubac on the crisis of the Dionysian hierarchical paradigm.Footnote ⁹ Their analyses show how, in the fifteenth century, the traditional linkage between divine hierarchy and ecclesial order – so central to medieval political theology – was destabilized by nominalism, humanism, and the rise of territorial states. Surprisingly, little attention has been paid to how Cusanus, whose early trilogy is structured around successive appropriations of the Dionysian corpus, responded to this broader transformation. The failure of Basel cannot be understood apart from this crisis of ecclesial intelligibility, nor can Cusanus’s speculative reframing of ecclesiology be detached from it.

Against this background, the present article proposes a new reading of Cusanus’s early trilogy. First, it reinterprets De concordantia catholica as a conciliar manual, composed within and for the unsettled practice of Basel itself. Second, it reads De docta ignorantia and De coniecturis as direct responses to the collapse of conciliar mediation and to the instability of hierarchical models of ecclesial order. Third, by foregrounding the 1442 letter to Rodrigo Sánchez de Arévalo and its description of the Church as an ecclesia coniecturalis, the article offers a framework in which Cusanus’s juridical, diplomatic, and speculative writings appear not as discrete phases, but as components of a single, historically grounded attempt to rethink the visibility of the Church amid the plurality of emerging modern forms.

IV. Speculative transformations

When Cusanus left the tumultuous Council of Basel in May 1437, together with a delegation of defenders of the pope, this marked a rupture in his biographyFootnote ¹⁰. Whether this rupture also implied that the political-philosophical question of the structure of authority and community would disappear from his writings, however, is far less obvious.Footnote ¹¹ As Jovino Miroy has pointed out, “no other Western thinker suffers from such a split image in the minds of scholars.”Footnote ¹² The unmistakable difference between De concordantia catholica and De docta ignorantia seems to suggest a discontinuity, yet the political stakes are not absent from Cusanus’s “philosophical-theological” works.Footnote ¹³

Miroy has shown convincingly that there is continuity between De concordantia catholica and De docta ignorantia.Footnote ¹⁴ Yet in his account, De coniecturis remains largely absent, even though Cusanus explicitly presents it as the sequel to De docta ignorantia and, like both of his earlier works, dedicates it to Julianus Cesarini, president of the Basel Council until the rupture of 1437. The neglect of De coniecturis is significant. In a letter to Rodrigo Sanchéz de Arévalo in 1442, written in the same period, Cusanus characterizes the church as an ecclesia coniecturalis. In a few other texts, he so clearly distances himself from the conciliarist movement, which in Basel had persisted and even elected its own counter-pope Felix V. Precisely what the conciliarists failed to see, Cusanus now makes explicit: the conjectural nature of the church, that it is visible in diverse external forms which can only be known in and through signs. These signs are never transparent: they carry rational meaning yet remain bound to the sensory and historical. The Church is not identical with its contingent forms but mediated through them as the mystical body of Christ.Footnote ¹⁵

Seen against the chaotic ecclesiastical and social conflicts of the fifteenth century, Cusanus’s concept of coniecturalis is more than a terminological novelty.Footnote ¹⁶ It provides a philosophical foundation that allows him to reposition the debate on authority and community. To understand its force, also De coniecturis (c. 1441–1444) must be read as a response to the same crisis of Basel that had generated De concordantia catholica. The three works are bound together by their common reference to Dionysius the Areopagite, who, throughout Cusanus’s career, provided a shifting yet constant horizon.

From the early Middle Ages onward, the Ecclesiastica Hierarchia had provided the basic grammar not only of Western ecclesiology but also of medieval society itself: a vision of Church and world as an ordered structure of mediations in which each rank participates in, and transmits, the divine light.Footnote ¹⁷ Yet, as Michel de Certeau reminds us, the same Dionysius is also the author of the Mystica Theologia, where all affirmative language collapses before the unknowability of God. This tension – between a visible hierarchical order and a mystical negation that exceeds every form – constitutes the deep structure of medieval thinking about the Church and its place within the social body. Cusanus inherits both poles, and the movement from De concordantia catholica through De docta ignorantia to De coniecturis can be read as his attempt to reinterpret this Dionysian dialectic at a moment when the traditional paradigm of Corpus mysticum was itself beginning to fracture.

Yet the Dionysian model itself was under severe strain in the late Middle Ages. Michel de Certeau has shown, building on Henri de Lubac, that the turbulence of the fifteenth century signaled the breakdown of the Corpus mysticum as a self-evident political-theological paradigm.Footnote ¹⁸ Nominalism had already detached concepts from the divine intellect, undermining the possibility of deriving social order directly from a metaphysical hierarchy. Conciliarism, inspired by authors such as Marsilius of Padua, radicalized this shift by deriving authority “from below.”

Against this background, the question of whether Cusanus’s speculative writings after Basel can still be read politically is not merely of antiquarian interest. It touches on the genesis of modern political thought itself. Is his appeal to Dionysius no more than the conservative reflex of a cardinal trying to preserve what could be saved? Or does his creative reinterpretation of Dionysian hierarchy offer resources to rethink precisely the emergence of a political theology that emancipated itself from God, yet continued to transport theological figures uncritically?

The crisis of Basel stands at the threshold of confessionalism, if only because of its inability to mediate papal and conciliar authority into a comprehensive unity. Already here emerges the awareness that the ultimate divine measure may appear in diverse historical forms. In De pace fidei (1453), Cusanus extends this awareness to Islam and other religions, transposing his model of concordantia to the geopolitical situation after the conquest of Constantinople by Sultan Mehmet II. The time is not yet ripe in 1440, but the question of how to deal with conflicting perspectives that reason cannot reconcile is already thematized. For this reason, the relation between De concordantia catholica, De docta ignorantia, and De coniecturis must be read against the ecclesiastical turbulences of Basel and the crisis of the Dionysian model itself. As Certeau observed, the crisis of Dionysian political theology coincides historically with the humanist “unmasking” of Dionysius by Lorenzo Valla – yet Dionysius continued to function, now not primarily as author of the Ecclesiastica Hierarchia, but as father of negative theology.Footnote ¹⁹

When the cardinal, canon lawyer, and philosopher Nicholas of Cusa wrote his letter to Rodrigo Sanchéz Arévalo in 1442 about the state of the Church, both of their active presence at the Council of Basel were already several years behind them. The Council had failed to find agreement between the two positions of the great debate over authority in the church – whether authority should be exercised by the Council as the representation of the local churches in relation to the secular rulers, or by the pope. Already here, the question is not merely who decides, but from where the church is to be observed: as an object to be fixed by institutional design, or as a communicative space whose visibility depends on practices of discernment.

In De concordantia catholica – the writing Cusanus composed during the eventful Council of Basel – his position in the debate concerning authority in the church is much less unequivocal. True, there are numerous passages in which he gives primacy to the authority of the Council over the authority of the pope. But unlike someone like Marsilius of Padua (1275–1342), the central purpose of the book is not to strengthen the conciliar position as such, as emphasized in most interpretations of this work.Footnote ²⁰ There are good arguments to be made, says Cusanus, for giving priority to the authority of the Council over the position of the pope in some cases, if only because it makes more sense to consider a matter from multiple perspectives. Not only the Council but also the Pope has an irreducible autonomy, and is an important actor in the ecclesial community. However, the central objective of De concordantia catholica is to show the harmony of the various spiritual forces that constitute the community. “Concordance is the principle by which the Catholic Church is in harmony as one and many – in one Lord and many subjects.”Footnote ²¹ This programmatic sentence frames the whole work: not a zero-sum verdict on supremacy, but a method to see the church where many voices sound together without erasing their difference.

For Cusanus, Dionysian hierarchy functions less as a static chain of command than as a dynamic order that enables unity amid plurality – even among positions that appear irreconcilable. What he finds in Dionysius is precisely this dynamism: the Church as a living community in which relations between spiritual powers are not fixed but evolve over time. The same holds for the shifting balance between pope and council, already evident at Basel. Concordantia, therefore, requires continual re-articulation, measured not by institutional supremacy but by the recognition that the Church is the living body of Christ, animated by a “spirit of brotherhood opposed to division and schism.”Footnote ²²

Conciliarism, too, must be understood as one possible contribution to concord – even if, unlike the angelic choirs, it allows considerable dissonance in the historical search for agreement. The real issue is not whether Cusanus was briefly a conciliarist who later changed camps, but how he grounds conciliar deliberation itself and the changeability of positions within it. In much of the literature, conciliarism is linked to the nominalist critique of universal concepts and the denial that human signs can express the absolute; this critique undermined the traditional claim that ecclesial hierarchy mirrored a divine order embodied in papal authority. Cusanus, by contrast, reinterprets hierarchy within a Dionysian horizon – not as a warrant for papal absolutism nor as nominalist dissolution, but as a dynamic structure in which difference belongs to order. The central question in De concordantia catholica is therefore how the real, God-given hierarchy relates to the shifting historical arrangements, laws, and power relations of the Church, and how conciliar conversation – including the pope’s participation – is possible within this tension. In short, how can the Church be seen, from within practice, as concordant difference?

To understand how Cusanus connects hierarchical order with the historical mutability of ecclesial arrangements, it is important to see how he situates De concordantia catholica within the conciliar debates themselves. From the outset, he frames the treatise as a practical manual for participants at Basel, written amid the “dissonances” that had unsettled many who were turning to “modern” authors.Footnote ²³ These new positions, he argues, must be read alongside earlier ones; concordance is both a synchronic and a diachronic task.

The work is therefore not a detached theory of Church and society, but a text produced within the practice of conciliar deliberation. It records arguments voiced at Basel, assembles canonical and theological precedents, and proposes a way of orienting oneself within the multiplicity of past and present voices. Cusanus’s key insight is that tradition is not a fixed deposit: earlier authorities appear differently when seen through contemporary controversies, and the reverse is equally true. This explains why patristic and canonical sources sometimes support conciliar authority and at other times papal primacy. Their meaning arises from the ongoing praxis of concordantia, which by definition cannot be final. The very dissonances Cusanus notes in the opening lines are, for him, signs of a living search for unity.

Thus, De concordantia catholica does not defend a single constitutional position. It is a handbook for conducting the conciliar conversation itself: a guide to discerning how diachronic and synchronic voices can be mediated into concordant practice. In this sense, Cusanus anticipates what later theory would call an internal observer’s standpoint: the Church cannot be viewed as an external object but only from within its communicative and historical life.Footnote ²⁴

As a handbook, De concordantia catholica does not offer a definitive distribution of power between pope and council – precisely because this is the question the council itself must resolve. For Cusanus, the council is a practice of concordia discors, where conflicting visions generate their own concord.Footnote ²⁵ To frame this, he turns to Dionysius’s Ecclesiastica Hierarchia, which grounds ecclesial communion in an ontological order. Yet this does not mean that the concrete ecclesiastical hierarchy simply coincides with the divine one. On the contrary, the gap between them creates space for change, disagreement, and deliberation. Hierarchy refers less to subordination than to each member’s relational place in the whole: fixed in the divine order, shifting in its earthly realization. Without this reference to the immutable, change itself would be impossible, and multiple consonances would become thinkable.Footnote ²⁶

This also explains why the council can possess an authority in some respects superior to that of the pope: the sound of many voices, even in dissonance, is more reliable than one. Yet the reverse is also true. The pope’s spiritual office limits the council’s claims just as conciliar plurality moderates papal authority.Footnote ²⁷ No position can therefore assume absolute authority. Ultimately, the Church is the mystical and living body of Christ – the orienting measure of all positions – yet this living body cannot be fixed in any single constitutional form. It becomes perceptible precisely where discordant voices are borne into concord without erasing their distinctness. For Cusanus, the irreducible difference between the divine hierarchy and its historical realizations creates the space in which interpretation, disagreement, and concord become possible. Plurality can only flourish against the background of the ultimate order described by Dionysius, yet that order never determines concrete arrangements once and for all.

This becomes clear in his engagement with Marsilius of Padua. Reading the Defensor pacis only after completing the first draft of De concordantia catholica, Cusanus found arguments that strengthened the conciliar character of the Church, especially regarding majority decisions and the council’s authority.Footnote ²⁸ Yet he also sharply rejected Marsilius’s claim that the bishop of Rome lacks special authority because it is not explicitly established by Scripture.Footnote ²⁹ Cusanus appeals to a long interpretive tradition – Alypius, Augustine, Optatus, and Jerome – to show that Scripture itself participates in ecclesial usage and does not terminate debate. A scriptural argument that forecloses interpretation, he insists, excludes itself from the very space of concordantia.

The same logic informs his discussions with the Hussites. In De usu communionis ad Bohemos (1433), written in the midst of negotiations at Basel, he argues that communion under both kinds can be permitted, yet cannot be made a condition for salvation.Footnote ³⁰ The Hussites err not in the practice itself but in absolutizing the scriptural warrant for it. Because Scripture admits multiple meanings and its authority is discerned through ecclesial reception, its interpretation belongs within the Church’s ongoing conversation. What Cusanus rejects, therefore, is any appeal – whether papal, conciliar, or scriptural – that closes the interpretive space in which concordant difference becomes possible.

We see in the interpretation of the Scriptures the various minds of men explicating various meanings; we see various opinions existing about the authority of the Scriptures; and we see it is possible for there to be inextricable doubt about their authority or their interpretation, leaving the minds of men in suspense. Where then will there be a reliable refuge for wayfarers? Surely, it is to be found in nothing else than in the usage and approval of the Church Militant, whether the doubt is about the Scripture, its authority and interpretation, or, outside Scripture, its authority and interpretation, or, outside Scripture, about a custom accepted by the Church.Footnote ³¹

This is where epieikeia (aequitas) enters. Though the term appears only marginally in De concordantia catholica, the principle shapes the whole work. In canon law, epieikeia limits every rule, since no norm covers all cases, and just rules can produce unjust outcomes. In a theological register, it names an authority higher than the rule: the measure that permits exceptions when required by the good of the Church. Hence Cusanus’s striking neologism epieikeizare: to act according to equity by keeping open the space between rule and life.Footnote ³²

For Cusanus, the Church is the living mystical body of Christ, and as such can never be reduced to any single doctrinal formulation or institutional structure. Life exceeds the rules that serve it.Footnote ³³ The concordantia catholica is therefore not a constitutional program but a handbook for maintaining the space in which divergent conceptions – ancient and “modern” – can be borne into concord. Where conversation hardens into static positions, concord becomes impossible.

At this point, however, the limits of conciliar practice become visible. De concordantia catholica succeeds in articulating the space between divine order and historical arrangements, and in keeping open the interpretive room required for concord. Yet it remains bound to the concrete procedures of deliberation and to the hope that such procedures can sustain unity in practice. The experience of Basel after 1437 revealed how fragile this hope was. When conversation hardened into institutional antagonism, the very conditions of concordantia dissolved.

It is precisely this impasse that necessitates a shift in register. If ecclesial unity can no longer be secured through juridical mediation alone, the question becomes more fundamental: under what conditions can unity be perceived at all, once no finite authority coincides with the measure of the Church? The problem Basel exposed in practice now demands an epistemic clarification. How can difference be acknowledged without abandoning unity, and how can authority be exercised without collapsing into domination?

Cusanus’s answer begins with De docta ignorantia. Here, the gap between divine measure and human articulation, already operative in conciliar practice, is reformulated as a universal condition of knowing. Only on this basis can the subsequent development of an ars coniecturalis become intelligible: as the practical method required to perceive the Church as one body within the irreducible plurality of its historical forms. The decisive question thus becomes how this epistemic reorientation can be translated into an ecclesial form: how the Church can be conceived as an ecclesia coniecturalis once unity itself can no longer be fixed by any single institutional or doctrinal measure.

De docta ignorantia addresses this question by rethinking the conditions of unity at the most fundamental level: if no finite measure can coincide with divine truth, then unity itself must be understood as mediated through difference rather than secured by institutional or doctrinal closure.

It is clear from the dedicatory letter to De docta ignorantia that Cusanus situates his new insight within the conciliar context. Returning from Constantinople in 1437 as papal legate – sent to bring the Greek representatives to the council of Ferrara–Florence – he reports an experience “on the ship, with the coast of Greece in view,” where he grasped that “the incomprehensible must be embraced in incomprehensible ways.”Footnote ³⁴ This moment marks a methodological shift. Precisely where the conciliar manual had reached its limits, Cusanus proposes a different genre and a different vantage point: docta ignorantia as the epistemic ground from which ecclesiology becomes thinkable again.

The guide in this shift is once more Dionysius, now above all the author of the Mystical Theology. Whereas De concordantia catholica worked within the framework of the Ecclesiastica Hierarchia, the new treatise turns to the apophatic insight that the relation between the finite and the infinite is marked by nulla proportio.Footnote ³⁵ The difference between divine order and ecclesial order that governed the earlier conciliar manual thus becomes an epistemological principle: the finite mind cannot grasp the absolute measure of things but can recognize its own noncoincidence with it. Learned ignorance is not skepticism, but a disciplined awareness that the measure we find is never the final one.

Accordingly, De docta ignorantia opens with a sustained analysis of the conditions of knowing. To know is to measure: to explore relations among things by means of a prior measure. Yet the mind never possesses the “precise measure”; it always knows from a determinate standpoint within the whole of possible relations. Only God measures absolutely, for God is the totality of relations. Human cognition, therefore, proceeds through comparative degrees, aware that every proportion presupposes a measure beyond itself. This awareness keeps interpretation open and prevents any doctrinal or institutional position from claiming finality.Footnote ³⁶

What De concordantia catholica had articulated as the gap between divine hierarchy and historical arrangements returns here as the structural condition of human knowing. The cosmos itself must be understood as constituted by proportional relations – hence the move in Book II to the contractum universum. Learned ignorance thus provides the epistemic architecture for the ars coniecturalis of De coniecturis: a method that allows the Church to be perceived not as a fixed order but as a living space where rule and life, doctrine and praxis remain in dynamic tension.

Thus, the infinite does withdraw from knowing, but at the same time the human mind cannot withdraw from the infinite – it itself participates in it, in actu. If knowledge is measuring, the cosmos itself must be understood as structured by such measuring relations: hence the turn to the concrete universe. This is the premise of the second book of De docta ignorantia on the maximum contractum. Chapter 11 involves a reflection on the place of the earth that cannot be the center. The argument presupposed here is the idea that in an infinite universe, simultaneously no point and simultaneously all points are centers. The real center is God, the maximum absolutum, which does not coincide with any of these points – God is the point that coincides with the circumference, something incomprehensible to the comparative mind, but whose incomprehensibility can be understood – and thus relevant to human praxis, to life in the world.Footnote ³⁷

It is a movement that allows the center point to become eccentric. This experience refers to Cusanus’s own journeys in his biography, but more so to the pilgrimage of the church in the temporal world, as he describes in De concordantia catholica.Footnote ³⁸ The search for the measure of concordantia, of harmony, opens the way to this concordantia, which at the same time remains always in motion – after all, the center is not the center. The concordance search begins anew at each point. At each point, the totality of all possible relations is present in a “contractive” way.Footnote ³⁹ Thus, there is an infinite number of universes, with an unending number of possibilities. Cusa refers to music as an example of a maximum contractum: the limited number of rules carries within it an infinite number of possibilities that can be actualized again and again.Footnote ⁴⁰ However, this infinite number of possibilities always refers to one concrete center. There is no human practice that is not characterized by this structure. In the fifth chapter of De docta ignorantia II, Cusanus makes an observation that shows how this structure of the contract universe also has implications for reading and interpreting ideas from the past. At issue there is the idea of the “all in all” that he finds with the Greek philosopher Anaxagoras. We can, says Cusanus, understand Anaxagoras better than he understood himself.Footnote ⁴¹ It is never possible to understand the thoughts of Anaxogoras other than from one’s own standpoint. But it is precisely from that vantage point that possibilities of the thought articulated by Anaxagoras open up, which he himself could not contemplate. Although Cusanus has not yet further explicated this thought here, it is consistent with the way he already thought in De concordantia catholica about dealing with rules and understandings – and even with the words of Scripture. It is in De coniecturis that he would develop this aspect of the “contract” universe. And it is no coincidence that it is precisely around this passage that the remarks appear in which he announces the book De coniecturis, then yet to be written.Footnote ⁴² Left at the level of structure, contraction would remain formal; the Incarnation binds it to history and grounds community – hence the culminating De ecclesia.

Yet the structure of proportion and contraction would remain abstract without its christological foundation. It is the incarnation that binds the infinite to the finite and grounds the very possibility of community. The concrete relationship between the finite and the infinite, which in a sense is a nonrelation (nulla proportio), also ultimately refers to the Christological dimension, as Cusanus makes clear in the third book. The historical appearance of Christ is the foundation and guarantee of the concrete connection between the finite and the infinite that takes shape in human life. The third book culminates in a long treatise De ecclesia, which makes explicit what has been implicit all along: that learned ignorance is not only a theory of knowledge but the ground of ecclesiology.Footnote ⁴³

This Christological dimension is often overlooked, especially among philosophical scholars.Footnote ⁴⁴ But it is precisely this comprehensive Christological finale that shows that in this book, Cusanus has developed a theory that must be seen against the background of the great church-political questions of his time. At the same time, it is the foundation of the idea that all these great questions make sense only insofar as they are existentially localized in the concrete life of each person and thus begin anew with each one.

For Cusanus, the historical incarnation is in fact the condition and actual reality “behind the signs” of this concrete presence of the absolute in every measuring praxis of the human mind. The absolute greatest, the ultimate measure, is not merely an abstract condition of the infinite play of measure and measured; precisely because Cusanus understands measuring as a living praxis, in which philosophical reflection also finds its place, therefore, the mystery of the living, historical God-man is the very foundation of the human capacity to deal with reality, as is already made clear in the introduction to De docta ignorantia.Footnote ⁴⁵

It is the orientation to the God–human nature of Christ that paradigmatically showed that behind the disproportion of the finite and the infinite lies precisely the presence of the infinite in concrete reality. The infinity of possible worlds thus becomes bound to the human person, in modern terms, the subject of reflection. The God–human relationship that came alive in Christ introduces an existential and practical dimension in thinking about the church.Footnote ⁴⁶

The dual nature of Christ actually represents paradigmatically the dual nature of every human being, who has the capacity to deal with this particular ambiguity of life and of reality. According to Cusanus, the never-stable relation between the finite and the infinite becomes, in Christ, inseparably bound to concrete human (sensory-rational) nature.Footnote ⁴⁷ Rudolf Haubst pointed out very early on that this Cusanian Christology philosophically presupposes the thought of man as microcosm.Footnote ⁴⁸ But, undoubtedly, it was also the inspiration of the Modern Devotion for whom the imitatio Christi suggested precisely a profound personal relationship to God that supported this Christological view. Not coincidentally, in the third book, Cusanus speaks of the veritas personalis, which is the foundation for man’s ability to know from his own center and point of view that there is an infinite number of possible centers and points of view.Footnote ⁴⁹ The question of community, posed in De concordantia catholica as it were “from the outside” (especially from the Ecclesiastical Hierarchy), is now addressed from another perspective – now from Dionysius’ Mystical Theology.

How is the community to be thought of when man (for a Christological background) is to be thought of as a microcosm? This question makes clear why De docta ignorantia ends as in a finale with a disproportionately long chapter De ecclesia (on the church). This chapter can almost be seen as a separate treatise, a position yet to be added, as Cusanus writes in its introduction.Footnote ⁵⁰ Entirely in keeping with the philosophy of the relationship between maximum absolutum and maximum contractum, Cusanus argues here that the greatest love cannot be attained by anyone, but that the greatest love is manifested by the infinite variety of forms in which love is loved, which is more in some, less in others, but can be attained for each in the her or his own greatest possible way. Love is the very bond of communion, but it is also that which precedes the difference between the finite and the infinite. “For church means to preserve the personal truth of each person and to be, without the mixing of natures and degrees, the unity of many.”Footnote ⁵¹

In Cusanus’s view, then, the unity of the church is by no means an abstract unity. It is a space of concordantia – a congregation of the most diverse positions, which are not reduced to a unified position. This image of the church stands in stark contrast to the attitude of the conciliar majority of Basel, who (in Cusanus’s eyes) managed to force the pope to issue decrees and change rules by manipulation. They acted in the mode of a voluntaristic exercise of power that was precisely not aimed at the ultimate ordering of all things. It was this handling of rules that, in Cusanus’s view, endangered the living unity of the church, the space of interpretation connected with every rule. Just as the difference between maximum contractum and maximum absolutum marks precisely the space in which people live, so too the space between rules and the ultimate ordering of things is a space for action. To keep open the space between the finite and the infinite is also to keep open the space between the actors of this community – such as the council and the pope, for example.

De docta ignorantia thus clarifies the epistemic condition exposed by the failure of conciliar mediation: no finite authority, concept, or institutional form can coincide with the truth it seeks to express. Yet this clarification raises a further and unavoidable question. If knowledge must be acknowledged as limited, how can judgment still be exercised responsibly? How can difference be navigated without collapsing into arbitrariness or paralysis?

It is at this point that De coniecturis becomes necessary. The work does not abandon the insights of docta ignorantia but responds to them methodologically. Where learned ignorance dismantles the claim to definitive knowledge, conjectural reasoning articulates the mode of judgment appropriate to such a condition. Significantly, both works are addressed to Julianus Cesarini, underscoring that this development is not merely speculative but oriented toward the unresolved problem of mediation that had defined the conciliar crisis. De coniecturis thus takes up the task that De docta ignorantia leaves open: to describe how unity, discernment, and action remain possible once certainty has been relinquished.

At the opening of De coniecturis, Cusanus explicitly presents the work as a continuation of De docta ignorantia. Having shown in the preceding books on learned ignorance that the ultimate precision of truth is unattainable, he now draws a methodological consequence: Cusanus explicitly formulates this shift when he writes that “every positive human assertion of truth is a conjecture” (omnem humanam veri positivam assertionem esse coniecturam).Footnote ⁵² Because the expansion of the grasp of truth is inexhaustible, finite human knowing bears no proportion to the highest truth. It is precisely this disproportion that transforms affirmative statements into conjectural judgments. Conjecture is therefore not a defect or provisional substitute for certainty, but the necessary mode of judgment appropriate to finite intellects.

This move is decisive for the continuity of Cusanus’s project. De docta ignorantia clarifies the epistemic condition exposed by the failure of conciliar mediation: no finite authority, concept, or institution can coincide with the truth it seeks to express. Yet that insight by itself does not explain how judgment remains possible once certainty has been relinquished. De coniecturis responds to this need by developing an ars: a disciplined practice of judging, comparing, and ordering perspectives under conditions of irreducible finitude. Conjectural reasoning neither suspends judgment nor absolutizes norms. Instead, it inhabits the space opened by learned ignorance, preserving orientation toward truth while acknowledging the limits of every determinate formulation.

At this point, the continuity with Cusanus’s earlier conciliar thinking becomes visible. What De concordantia catholica articulated in juridical terms through the principle of epieikeia – the equitable correction of general norms in view of concrete circumstances – reappears here at a methodological level. Conjectural judgment generalizes this logic beyond canon law, describing the form of discernment required wherever unity must be maintained without the guarantee of definitive determination.Footnote ⁵³

The ecclesiological significance of De coniecturis emerges most clearly in its sustained reflection on plurality. Throughout the work, and especially in Book II, Cusanus emphasizes that every finite perspective is partial, relational, and proportionate.Footnote ⁵⁴ No standpoint can claim exhaustive access to truth; each contributes according to its measure. Difference is therefore not an obstacle to unity but a condition of its appearance. Unity does not arise through the elimination of plurality, but through the ordered relation of diverse perspectives within a shared orientation.Footnote ⁵⁵

De coniecturis further radicalizes this account of plurality by grounding it in the concrete activity of the human mind itself. Conjectures arise from the mind insofar as it participates, as the living image of God, in the fecundity of creation. The human intellect gives form to a conjectural world, just as the divine intellect gives form to the real.Footnote ⁵⁶ Unity, on this account, is not an abstract principle imposed upon plurality, but the living center in which the manifold of conjectures is related to God as their measure. The ordered plurality of perspectives thus reflects not fragmentation, but the dynamic participation of finite minds in a truth that exceeds them.

The ars coniecturalis is articulated in De coniecturis as a mode of judgment applicable to the whole of reality, and Book II explicitly extends its scope to the ordering of the world as such.Footnote ⁵⁷ Yet the Church does not appear here as one possible application among others. Rather, it functions as the concrete and historical presupposition of conjectural mediation itself. As the living body of Christ, the Church names the space in which human plurality is already related to a divine measure without collapsing into identity. Ecclesial unity does not consist in uniformity, nor can it be secured by the dominance of one perspective over others. The Church becomes visible where conjectural judgment is sustained as a shared practice that holds together difference and concord. In this sense, the ars coniecturalis does not merely describe a general epistemic procedure; it receives its historical intelligibility in the ecclesial form of life that sustains conjectural mediation over time.

Read against the background of Basel, this marks a decisive reconfiguration. Where conciliar procedure sought unity through juridical representation and constitutional order, conjectural reasoning seeks unity through interpretive concord. De coniecturis thus provides a framework for understanding how the Church can remain one body amid divergent historical, cultural, and theological perspectives, even when no single form can claim to embody that unity exhaustively.

A further ecclesiological dimension of De coniecturis comes to the fore in its symbolic grammar of proportion and relational order. Especially in Book II, Cusanus employs the language of harmony, measure, and bodily relation to describe how multiplicity can be ordered without being reduced. Unity is not imposed from above but emerges from the coordinated relation of distinct elements, each contributing according to its proportion.Footnote ⁵⁸

This symbolic register resonates closely with the corporeal and harmonic imagery developed in De docta ignorantia II–III, where the coincidence of unity and multiplicity is explored through figures of body, proportion, and concordance. Read together, these texts illuminate Cusanus’s understanding of the Church as a living body whose coherence depends on the ongoing mediation of difference rather than on juridical aggregation or hierarchical domination. Ecclesial order is thus dynamic rather than static, enacted rather than guaranteed.

In this perspective, the ars coniecturalis articulates the mode by which the Church lives as corpus Christi under conditions in which no single form can exhaust its meaning. Yet this conjectural mode of ecclesial existence presupposes more than epistemic humility or interpretive skill. It is sustained by a practical orientation of caritas: a form of love that binds unity and difference in lived relation.Footnote ⁵⁹ Love, in this sense, is not an added moral supplement but the dynamic praxis that holds unitas and alteritas together without dissolving their tension. Through such loving mediation, judgment and discernment become possible as shared ecclesial practices, enabling the Church to participate in Christ’s living body while remaining open to the plurality of its historical forms.

Taken together, these dimensions clarify why De coniecturis is indispensable for understanding Cusanus’s notion of the ecclesia coniecturalis. Conjectural judgment names the practical form of unity appropriate to a Church that can no longer rely on constitutional closure or hierarchical triumph. It provides the methodological bridge between the epistemic humility of De docta ignorantia and the ecclesiological reconfiguration articulated in Cusanus’s later writings, including the 1442 letter to Arévalo.

The ecclesia coniecturalis does not denote an indeterminate or merely provisional Church. It names a mode of ecclesial existence in which unity is continuously enacted through equitable and conjectural mediation. Such mediation presupposes a shared practical orientation – caritas – through which unity and difference are held together as a lived ecclesial relation. In this way, De coniecturis transforms the failure of conciliar procedures into a reflective practice capable of sustaining concord without suppressing plurality. What Basel could not achieve institutionally, Cusanus seeks to retrieve methodologically: a vision of the Church as a living community in which unity remains visible precisely through the mediation of difference.

Cusanus’s later ecclesiastical career does not contradict the trajectory traced in this article; it brings its underlying logic into sharper relief. His elevation to the cardinalate in 1448, his governance as bishop of Brixen, and his service as vicar of Rome under Pius II attest to a sustained commitment to the Church’s hierarchical offices. Yet in Cusanus’s thought, hierarchy is never self-justifying. Already in De concordantia catholica, authority is consistently mediated through the canonistic principle of epieikeia: the equitable judgment that corrects the rigidity of general norms in view of concrete circumstances and the Church’s ultimate end.

In this respect, Cusanus stands within a Dionysian tradition in which hierarchy is conceived not as self-grounding power, but as a relational order that mediates divine truth through finite forms – a tradition he creatively reinterprets under the altered historical conditions of the fifteenth century.Footnote ⁶⁰

What De coniecturis develops under speculative auspices is not a departure from this logic but its methodological generalization. The ars coniecturalis does not replace equity; it generalizes it. Where epieikeia governs the prudent application of law within juridical and ecclesial structures, conjectural judgment articulates the epistemic conditions under which such prudence becomes possible at all. In this sense, epieikeia appears as the juridical anticipation of a broader conjectural logic, in which unity can only be sustained through mediated judgment rather than through the direct coincidence of norm and application. Because no finite form – legal, institutional, or doctrinal – can exhaust the truth it signifies, authority must operate through interpretive mediation rather than through formal supremacy.

Read in this light, Cusanus’s ecclesiology neither dissolves hierarchy nor absolutizes it. Hierarchical office provides the locus of judgment, not its guarantee.

For Cusanus, the pope is not an absolute sovereign who resolves ecclesial plurality by fiat, but an orienting point within a conjectural space of mediation. Papal authority functions not as the closure of conflict, but as a principle of reference through which divergent perspectives can be ordered without being eliminated. The Church’s unity is preserved through practices of equitable and conjectural discernment that hold together rule and contingency, order, and historical plurality. Cusanus thus rethinks authority from within its highest institutional forms, transforming conciliar failure into a reflective practice capable of sustaining ecclesial unity under conditions of irreducible difference.

In this sense, the ars coniecturalis generalizes the canonistic logic of epieikeia by opening a broader horizon in which the Church can be perceived as the living body of Christ. Ecclesial life cannot dispense with rules and institutional forms, yet it never coincides fully with them. The life of the Church unfolds in the space of mediation that such norms presuppose but cannot exhaust – a space in which judgment, discernment, and participation in Christ’s own life take precedence over formal determination.

V. Conclusion: Basel’s Legacy and the Ecclesia Coniecturalis

Seen from the vantage point of Basel, Cusanus’s later development appears less as a departure from ecclesiology than as an attempt to retrieve, at a deeper level, what the conciliar experiment itself could not secure. The council exposed the limits of a juridical imagination that sought to guarantee ecclesial unity through constitutional design alone, at a moment when emerging territorial powers, competing claims to authority, and the erosion of the older Dionysian synthesis rendered such guarantees increasingly fragile. De concordantia catholica registers these tensions from within the conciliar process, yet that same process ultimately stalled as its positions hardened and its mediating capacity collapsed.

The writings that followed – De docta ignorantia and De coniecturis – do not abandon the conciliar question but relocate it. They transform Basel’s unresolved conflict into a reflection on the conditions under which the Church can still be perceived as one body amid irreducible plurality. The ecclesia coniecturalis thus emerges as Cusanus’s response to a historical impasse: an attempt to think ecclesial unity not as institutional supremacy or constitutional closure, but as a practice of interpretation grounded in epieikeia and sustained through conjectural judgment. Where juridical norms alone proved insufficient, equitable discernment and interpretive mediation become the means by which unity remains possible.

In this sense, Cusanus stands at a historical threshold. His vision preserves the conciliar insight that authority must be mediated through the community, while reinterpreting that insight within a broader theological and epistemic horizon that anticipates the modern problem of plurality. The Church becomes visible where differentiated voices are born into concord without being reduced to uniformity – where rule and life, doctrine and practice, remain in dynamic reciprocity. Ecclesial order is neither dissolved nor absolutized; it is enacted through practices of judgment that hold together institutional form and living participation in Christ.

Situated within the crisis of the fifteenth century, Cusanus’s notion of the ecclesia coniecturalis illuminates both the failure and the promise of Basel. It offers historians a way of reading the late medieval Church beyond fixed constitutional models, as a living hermeneutical community in which unity is continually re-enacted under changing historical conditions. In this respect, Cusanus’s contribution is not merely speculative but decisively historical: a witness to how a canonist, diplomat, and churchman sought to reimagine ecclesial concord at the very moment when its medieval forms were coming undone.