Unicity of Intellect
The concept of the unicity of the intellect emerged in association with interpretations of Aristotle’s theory of the soul distinguishing between the agent and the possible intellect. The term monopsychism is connected with the controversy, which arose in the Middle Ages with Averroes’ (Ibn Rushd) commentary on Aristotle. Averroes considers not only the agent intellect but also the material (possible) intellect as transcendent and numerically unified. Thomas Aquinas and other Christian thinkers criticized this doctrine because it negates the concept of an individual immortal human soul. In the fifteenth century, the unicity of the intellect was often viewed as an interpretation fully in agreement with Aristotle’s theory of the soul, and the doctrine is usually found in Renaissance Paduan Peripatetic philosophers, beginning with Paul of Venice and ending with Nicoletto Vernia. Criticism of the doctrine (particularly by Marsilio Ficino) influenced, however, the Church reaction and led to the condemnation of monopsychism at the Fifth Lateran Council in 1513. The anti-Averroist attitude began to prevail in the sixteenth century. As a result of Pietro Pomponazzi affair, the subject of discussion shifted from the relationship of plurality versus unicity to the issue of immortality versus mortality. Monopsychism consequently declined both as a philosophical doctrine and as a viable interpretation of Aristotle in the second half of the sixteenth century.
Heritage and Rupture with the Tradition
Aristotle in On the Soul (Aristotle 1961), 3.5.430a) distinguishes between two types of “intellect” – one that “becomes all things,” i.e., is able to assume all forms, and the other which is capable of making forms actual in the mind. Aristotle does not further specify the latter type of intellect that in the subsequent tradition understood as the agent intellect (intellectus agens), unlike the first type which is usually referred to as the material intellect (materialis), or the possible intellect (possibilis). The aforementioned passage of Aristotle’s On the Soul inspired his Greek commentators to produce various interpretations of the ontological status of the first or the second intellect. Although the unicity of the agent intellect was adopted by a number of Greek (Alexander of Aphrodisias, Themistius), Muslim (Avicenna), and Christian medieval philosophers (Dominik Gundisalvi), a major controversy did not arise until the unicity was also attributed to the possible (material) intellect. In his Long Commentary to Aristotle’s On the Soul, Averroes (Ibn Rushd) describes not only the agent intellect but also the material (possible) intellect as transcendent and numerically unified, considering it the last nonphysical substance. For many Christian thinkers, the implications of this doctrine on the unity of the possible intellect, called monopsychism, were unacceptable. Monopsychism was in conflict with the concept of an individual immortal human soul, since according to Averroes, what is individual and intrinsic to humans, i.e., the so-called passive intellect (intellectus possibilis), ceases to exist together with the body, whereas the possible intellect, made actual by the agent intellect, is immortal, but unified, like the collective reason of all of mankind, which in every single individual works so that it uses its notions in order to abstract the ideas therefrom.
If the material intellect (intellectus materialis) is multiplied according to the number of individual men, it would be an individual thing – hoc aliquid – a body, or a power in a body. However, hoc aliquid is a concept of the mind that only exists as a possibility. And this concept of the mind in potency is the subject of the material intellect. This implies that the material intellect would serve as its own subject, setting itself in motion and knowing itself, which is impossible (Averroes 1953, p. 402).
If the material intellect (intellectus materialis) was multiplied according to the number of individual men, knowledge would also be endlessly multiplied. Your and my knowledge of the same object would be numerically different although, as regards its nature, it represents an identical object, which is nonsense (Averroes 1953).
It would not be possible for students to learn something from their teachers. The teachers’ knowledge would have to have the power to affect and produce students’ knowledge (Averroes 1953, p. 411).
Thomas Aquinas, in contrast, in his De unitate intellectus contra Averroistas contests Averroes’ interpretation of Aristotle and rejects not only the unity of the possible intellect but also the unity of the agent intellect. According to Aquinas, the intellect is one of the faculties of the individual soul which is a form of the body. The theory of the unity of the intellect would contradict the fundamental experience underpinning Aquinas’s argument that individual human beings do in fact understand (Aquinas 1976).
Following Thomas Aquinas, the doctrine on the unity of the possible intellect became the basic characteristic of Averroism. Despite the fact that Aquinas in his day gave rise to the “phantom of Latin Averroism” (Marenbon 2013), a number of philosophers in the fifteenth and sixteenth century in one way or another advocated the unicity of the intellect and were therefore known as “Averroists” (Martin 2013, 2014).
Innovative and Original Aspects
Advocates of Monopsychism
Averroism was traditionally discussed during the Renaissance at the University of Padua. The first advocates of monopsychism in the Renaissance allegedly included Paul of Venice. According to him, the possible intellect that becomes all things, i.e., understands the universals that are immaterial and eternal, has to possess these qualities. Being of an immaterial nature, it has to therefore be unique since a multitude arises from matter (Nardi 1958; Kuksewicz 1983). At the same time, Paul of Venice conceived the intellect as the substantial form of the human body, i.e., intellect was not connected with the body merely in the sense of activity, but also infused it with essence. This notion is close to Thomas Aquinas and seems to be in opposition to monopsychism (Conti 1992).
The thoughts of Paul of Venice were further elaborated by Gaetano da Thiene, who, however, rejected Averroes’ monopsychism. Although, according to Gaetano, the unicity of the intellect enables us to understand the general, if the intellect does not pertain to humans as a substantial form, it is impossible to define man as a rational being (Kessler 2008).
Unlike Gaetano, a number of philosophers associated with the Paduan school were propagators of the Averroist doctrine. Although Niccolò Tignosi sided with Thomas Aquinas and adopted his doctrine on the soul as a substantial form, he believed that the true character of the doctrine on the unicity of the intellect depended on the “opinion of the faith” (opinio fidei). Rational arguments supporting the plurality of immortal souls are viewed as too weak, and, therefore, in relation to the natural intellect, Averroes’ unicity theory must be approved (Hasse 2004a).
Johannes Argyropoulos in his commentary on De anima openly acknowledges Averroes’ understanding of the agent intellect as a single and separated entity and also the unicity of the possible (material) intellect and finally even the concept of the mortal “passive” intellect (Monfasani 1993).
Like his predecessors, Elia del Medigo elaborated on Averroes’ commentary on Aristotle’s teachings in his two Tractates on the Soul. Averroes’ possible intellect is originally considered a mere disposition which is, however, gradually becoming an immaterial substance as it approaches the separated active intellect until the final unification (Bland 1995). Del Medigo interprets the relationship between the possible and agent intellects with reference to the Kabbalist tradition that culminated in a mystical unicity.
Del Medigo’s pupil, Giovanni Pico della Mirandola, in his Conclusiones (1486) consequently presents 900 theses encompassing different philosophical traditions aiming to bring them in agreement, including Averroes’ statement: “There is a single intellective soul for all humans” (Farmer 1998). Mirandola was convinced, however, that the theory of the unicity of the intellect was compatible with the immortality of the individual soul. This was described by Mirandola as the unicity of the intellect with the separated intellect in the state of happiness (Still 2008).
The term “Averroism” is most often attributed to Nicoletto Vernia thanks to his tractate on the substantial unity of the human intellect (Utrum anima intellectiva humano corpore unita). In this work, Vernia defends Averroes’ monopsychism as the only correct interpretation of Aristotle’s psychology. Vernia believed that efforts by Aquinas and other medieval authors to assert the doctrine of the individual soul as a substantial form of the human body, separable from the body after death, were completely alien to Aristotle’s thought. Conversely, Peripatetic thought, supported by Averroes’ interpretation, postulates the intellective soul to be eternal and not multiplied, since immaterial entities are not subject to individuation (Mahoney 2000). For Vernia, the possible intellect is eternal and eternally connected with the agent intellect, i.e., as a separate substance possessing eternal intellectuality (Hasse 2004b).
Vernia’s teachings represent the climax of the doctrine on the unicity of the intellect in the fifteenth century. Vernia and additional fifteenth-century thinkers viewed Averroes’ concept of the possible intellect as a single, separate, superindividual substance as an interpretation fully in agreement with Aristotle’s doctrine on the soul. This doctrine was at the same time in contradiction with the Christian belief in the immortal, individual human soul.
Criticism of Monopsychism
Opponents of monopsychism during the Renaissance were primarily thinkers who followed up on the teachings of Thomas Aquinas or who directly drew on his legacy. As one of their sources, they could have relied on the decree of the Council of Vienne (1311–1312) which banned the theory that the intellective soul is not a substantial form of the body and declared it a heretical doctrine, thus supporting the Thomist concept.
Aquinas’s argumentation against the unicity of the intellect also inspired Nicolaus Cusanus whose Idiota de mente (Cusa 1983) explicitly criticized the doctrine perpetuated by “some Peripatetic” about “a single intellective soul.” Cusanus rejects the unicity of the intellect on the grounds of the proportionality of the individual soul and the human body. Since the identity of the proportion cannot be multiplied, the identity of the mind animating the body in an adequate proportion cannot be multiplied either. Cusanus therefore inferred that it was impossible for all humans to share the same intellect. Similar to Thomas Aquinas, Nicolaus Cusanus condemned monopsychism for its inability to explain the experience of the individuality of thinking. His arguments are underpinned by the concept of the soul as an essential form of humans or Aquinas’s concept of the intellect as the capability of the soul which is a substantial form of the human body (Führer 2014).
Numerous Renaissance Platonists were critical of the doctrine of monopsychism. In his In calumniatorem Platonis, Cardinal Bessarion saw a difference between interpreting Aristotle in the sense of Alexander’s rejection of immortality and Averroes’ refusal of individuality. Given the eternal nature of the world, if we want to retain individuality and avoid Alexandrian mortality, we either have to adopt the doctrine on transmigration of the souls (metempsychosis) or the infinite number of souls. These contradictions may be resolved by means of Averroes’ postulation of a single intellect common to all. According to Bessarion, monopsychism thus presents an adequate interpretation of Aristotle’s philosophy, although it fails to stand the test of Christian faith, and needs to be replaced by Platonism which, unlike Aristotelianism, is in harmony with the Christian faith (Martin 2014).
Monopsychism was contested by Marsilio Ficino, who dedicated the entire 15th volume of his Platonic Theology (Theologia platonica de immortalitate animorum) to Averroes’ doctrine. Ficino points to the absurd consequences that would stem from the unicity of the possible and the agent intellect (Allen 2013). Ficino finally resorted to an eclectic formulation: adopting the concept of the immortality of the possible intellect from Averroes’ teachings and the multiplicity of souls from Alexander of Aphrodisias. Ficino refuses to regard matter as the principle of individuation, which prevents him from sliding into one of the extremes and for the Christian faith unacceptable interpretations of Aristotle’s doctrine of the intellect. If the intellect is not individualized by matter, it loses both its immortality, which would have stemmed from its connection with the body, and its Averroist superindividuality and unicity of the eternal intellect separate from matter (Blum 2007).
It was presumably the effect of Ficino’s criticism of Averroism (Randall 1961) that led the Bishop of Padua, Pietro Barozzi, in May 1489 to issue a decree forbidding public debates on the Averroist doctrine on the unicity of the intellect. In response to the condemnation of monopsychism, Nicoletto Vernia produced the tractate Against Averroes’ Perverse Opinion on the Unicity of the Intellect (Contra perversam Averrois opinionem de unitate intellectus) in which he reviewed his original Averroist approach. Vernia here claimed that although he lectured on Averroes’ monopsychism, he saw it only as a dialectic exercise, and he himself was not an advocate of the monopsychist doctrine. In his new tractate, he not only opposed Averroist arguments, but even attempted to demonstrate the individuality of the immortal human soul (Hasse 2004b).
The publication of Barozzi’s decree was shortly followed by an anti-Averroist tractate by the Franciscan and Scottish Antonio Trombetta. Despite the anti-Averroist character of the treatise, Trombetta believed Averroes’ theory on the indestructibility of the soul to be congruent with Aristotle’s teachings as well as with Christian faith. Trombetta intended to support both the eternal nature of the intellect understanding universals and the plurality of the intellect (Blum 2007).
Aristotelian thinkers found the rejection of the Averroist unicity of the intellect problematic. In his Quodlibeta de intelligentiis published in 1494, Alessandro Achillini still viewed Averroes’ interpretation of the intellect as the correct approach to Aristotle’s problem. Although he accentuated the fact that the doctrine on the unicity of the intellect contradicted the faith and also had to be disputed by means of philosophical arguments, he also employed pro-Averroist arguments. If the possible intellect would be multiple in its nature, it would be impossible, due to its individuation, to distinguish it from sensory perception, and it would be impossible to obtain knowledge of universal forms. Achillini rejected in the end the unicity of the intellect, although it seemed probable in philosophical terms, and the philosophical arguments raised against this theory were insufficient (Hasse 2004b).
Vernio’s students Agostino Nifo and Pietro Pomponazzi similarly admitted in their early works that Averroist monopsychism appears to be the right interpretation of Aristotle which is difficult to refute. In his commentary on Aristotle’s De anima, Agostino Nifo expounded on Averroes’ monopsychism applying cosmologic terms, i.e., referring to a heavenly sphere, which he identified with the human intellect, and yet considering this doctrine unacceptable for Christian believers. As early as 1503, however, he published De intellectu, in which he rejected the entire doctrine. He does not rely on psychological and epistemological counterarguments, however, as those were not found convincing, but formulated objections drawing on ethical philosophy and religion as well as on arguments derived from natural philosophy and cosmology (Hasse 2004a, b).
It seems that even Pietro Pomponazzi in his early commentaries on Aristotle regards monopsychism as a legitimate interpretation of Aristotle. He paraphrases Averroes’ position, confronting it with the explication by Alexander of Aphrodisias, i.e., with the plurality of individual mortal intellects. Averroes’ doctrine on the soul is considered congruent with Aristotle’s teachings, but useless and therefore not worth following. Alexander’s interpretation of Aristotle’s text did not prevail in Pomponazzi’s argumentation until the 1520s (Pluta 1986; Van Dooren 1994).
Impact and Legacy
The oscillation of many philosophers between Averroist monopsychism on the one hand and Alexandrian emphasis on plurality at the cost of rejection of immortality on the other became one of the issues addressed by the Fifth Lateran Council. The bull “Apostolici regiminis” issued by Leo X on 19 December 1513 forbade the advocacy of both the Averroist and the Alexandrian position, even in the form of a mere dialectic exercise.
Pietro Pomponazzi’s Tractatus on the Immortality of the Soul published in November 1516 caused controversy, however, due to his inclination to Alexandrianism, not Averroism. Pomponazzi rejected the unicity of the intellect, arguing in favor of the plurality of souls, to which he, however, attributed only relative immortality and absolute mortality. Pomponazzi’s key argument against the unicity of the intellect was a thesis adopted from Aristotle arguing that the activity of the intellect cannot do without imagination, and it was therefore dependent on phantasmata, sensory images, produced by sensory perception. According to Pomponazzi, if the intellect is dependent on the body in terms of its activity, it depends on the body in terms of its existence, hence being individualized through the body.
The unicity of the intellect, condemned at the Council, was consequently rejected on the basis of philosophical arguments using an analysis of the process of knowledge. Thanks to Pomponazzi, the discussion subsequently shifts to a different level; the relationship of plurality versus unicity made way to the issue of immortality versus mortality. Pomponazzi himself differentiated between the agent and the possible intellect, viewing the agent intellect as an immortal and separate substance which affects the possible intellect, individualized through the body, just as the mover affects the moved. Gasparo Contarini, one of Pomponazzi’s critics and advocates of the immortality of the human soul, also agreed with Pomponazzi not only in his rejection of Averroist monopsychism but also in viewing the agent intellect as separate from the human soul (Contarini 2014). Cesare Cremonini later held the same position – on the one hand the immanency of the possible intellect and the transcendence of the agent intellect – while at the same time identifying the unified agent intellect with God (Kuhn 1996). As with Pomponazzi, Cremonini also drew on the thoughts of Alexander of Aphrodisias, similarly to Simone Porzio earlier, who, however, unlike Cremonini, rejected Alexander’s identification of the agent intellect with God (Garin 2008).
One exception in the debate in the period in question, which began to be dominated by the anti-Averroist attitude, was Luca Prassicio, who defended Averroes as an advocate of the immortality of the soul both against Pomponazzi and Nifo. In his tractate on the immortality of the soul, he chose to support Averroes as the best advocate of the immortality of the soul, i.e., not only the agent but also the possible intellect. In Prassicio’s theories, the problematic aspect of the concept of the unicity of the possible intellect from the perspective of Christianity curiously made way to the advocacy of the immortality of the soul, challenged by Pomponazzi (Hasse 2004b).
The second half of the sixteenth century consequently saw the doctrine on the unicity of the intellect and Averroism as a declining trend. One of the last philosophers to contribute to the topic of the Averroist unicity of the intellect was Francesco Vimercato, who in his writings on the soul arrived at the unicity of the active as well as the unicity of the possible intellect, although again, like many of his predecessors, he also claimed that this doctrine was incompatible with Christianity. The last advocate of the unicity of the intellect in terms of natural philosophy, although also emphasizing its falsity in the sense of Christian truth, was presumably Antonio Bernardi in 1562 (Hasse 2004a).
The gradual disappearance of Averroist thought in the second half of the sixteenth century also does not imply that philosophers would stop objecting to his theory. So-called Conimbricenses and Francisco de Toledo regarded Averroes’ monopsychism as a doctrine contradicting Aristotle’s teachings and the true doctrine (Salatowsky 2006). The elaboration of alternative theories of intellection based on Aristotle’s theories was actually the reason for a retreat from Averroist positions, both in Lutheran Germany by Philip Melanchthon and in Jesuit scholasticism (Wels 2000), represented by Francisco Suárez, or as part of Aristotelianism of Jacopo Zabarella (Hasse 2007). The last serious attack on Averroist monopsychism was in all probability formulated in the seventeenth century by Cambridge Platonists, most notably Henry More, although this critique was articulated from the Platonist perspective (Hutton 2013).
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