Dominik Perler

Eustachius studied philosophy and theology in Paris, obtained a “license” in 1604, and taught philosophy at the Collège de Calvi, an arts college associated with the Sorbonne. In 1606 he entered the Feuillants, a Cistercian order, and became involved in the education of the members of the order. Eustachius was the author of the Summa philosophiae quadripartita (1609), an influential survey of late Scholastic Aristotelianism. Its four parts cover the main areas of philosophy: logic, ethics, natural philosophy, and metaphysics (see Ariew et al. 1998, 69–71). In a letter to Mersenne from 1640, Descartes remarked that he had bought a copy of this work, “the best book of its kind ever made” (AT III 232, CSMK 156). He intended to print it with critical comments to compare traditional Aristotelianism with his own philosophical program, but he never carried out this plan. The reasons are unclear. Perhaps he feared that an open attack on Scholastic philosophy would upset traditional philosophers, especially those teaching in the universities, and prevent them from approving his Meditations. Perhaps he was busy with other projects in subsequent years, in particular with his extensive correspondence and his replies to the objections written against the Meditations. Or perhaps he abandoned the project because he was unable to secure Eustachius's permission, since the latter died in 1640 (see AT III 260, CSMK 161). The Summa, which combines elements from Thomism and Scotism, contains many traditional doctrines, among them syllogistic logic, hylomorphism, an account of the four Aristotelian causes, and a theory of categories. It is hardly surprising that Descartes chose it as the target of his critique because it provided a much shorter account of traditional Aristotelianism than the long Jesuit commentaries, known as the “Conimbricenses,” or the extensive treatises by Franciscus Toletus and Antonius Rubius (Gilson 1913, Ariew 2011). He believed that anyone who had the chance to read his comments on this book would easily see its deficits and “learn to scorn it at the same time” (AT III 259–60, CSMK 161). Despite this harsh critique, there are striking similarities between the Scholastic doctrines expressed by Eustachius and Descartes’ own opinions (Van der Pitte 1988). The most obvious parallel is in the theory of ideas (Perler 1996).

Descartes famously claims that mind and body are really distinct substances, a view known as substance dualism (AT VII 78, 169–70; CSM II 54, 119–20). This claim is part of a larger theory of distinctions, which has both a metaphysical and an epistemological side. On the one hand, it explains what kinds of entities there are in the world and how they are related to each other; on the other, it also spells out how we can gain knowledge of these relations and how we are thereby able to provide an adequate description of the world – a description that fits not only human beings but also purely material substances (e.g., plants and animals) and purely mental substances (God and angels) as well as their attributes and modes. The theory of distinctions has Scholastic roots. It was originally developed to resolve various theological puzzles (e.g., the connection between the three divine persons and the relation between God's essence and his attributes) but soon became a general instrument for distinguishing different types of metaphysical relations (Adams 1987, 16–29). Descartes came to know it through late Scholastic authors, among them Francisco Suárez and Eustachius a Sancto Paulo (Ariew 2011), and used it primarily in a nontheological context (for an application to some theological problems, see Armogathe 1977). On his view, which he sets forth in detail in Principles I.60–62, there are three types of distinction. First, there is a real distinction. It obtains between two or more substances, and we can recognize it “from the fact that we can clearly and distinctly understand one apart from the other” (AT VIIIA 28, CSM I 213). This is precisely the distinction that exists between mind and body, but also between two (or more) minds and, should there be more than one, between two (or more) bodies (see individuation and substance).

Despite his famous claim that mind and body are really distinct substances, Descartes repeatedly points out that a human being is not a mere composite of two entities. For example, he calls the human being “a true ens per se” and asserts that the mind “is united in a real and substantial manner to the body” (AT III 493, CSMK 206). If we intend to give a full account of a human being, we need notions not just of mind and of body but also of the union of mind and body – the latter notion being as primitive as the other two and therefore irreducible to them (AT III 665, 691; CSMK 218, 226). Only this third notion enables us to describe and explain the features that are distinctive of a living human being – namely, sensory perceptions and passions (see primitive notion). Given this thesis, it is hardly surprising that Descartes does not conceive of himself as a purely immaterial mind once he has completed an analysis of mind and body. Nor does he claim that his body is only accidentally connected to his mind, serving as a mere instrument. In the Sixth Meditation, he unmistakably holds that his mind is not in his body as a sailor is present in a ship. It is rather “very closely joined” to the body and, as it were, “intermingled with it” (AT VII 81, CSM II 56). Should there be no intermingling, no sensations of hunger, thirst, and pain could arise, because it is neither the mind alone nor the body alone that has these states, but the union of mind and body.

Unlike most of his late medieval contemporaries, Nicholas of Autrecourt did not subscribe to Aristotelianism. Instead, he radically challenged the foundations of Aristotle’s metaphysics and epistemology by asking two questions: first, how are we supposed to explain the basic constituents of the world, given that the Aristotelian categories are mere theoretical constructions and not immediately perceivable? Second, what can we know with absolute certitude, given that sense perception – the starting point in Aristotelian epistemology – is fallible and unreliable? Focusing on these two questions, Nicholas elaborated an atomistic metaphysics and defended an epistemology that emphasizes knowledge of a logical principle (the principle of non-contradiction), dismissing all knowledge based on inductive reasoning as uncertain.

The French scholastic philosopher and theologian Hervaeus Natalis was not only one of the most influential early Thomists, but was also an original thinker who made an important contribution to the medieval debate on intentionality. He examined carefully the ontological question of what intentional objects are, and discussed the epistemological problem of how they are generated in a cognitive act. Hervaeus argued that intentional objects are ‘third entities’ that cannot be reduced to extramental or mental entities, a thesis that sparked controversy in the fourteenth century.

Although Dante never received a systematic training in philosophy, he tackled some of the most controversial philosophical problems of his time. In his theory of science, he asked how we are to explain the fact that science is a unified, strictly ordered system of knowledge. He answered by comparing the scientific disciplines with the celestial spheres, claiming that the system of knowledge mirrors the cosmological order. In his political philosophy, he asked why all humans want to live in a peaceful society. All humans seek full use of their cognitive capacity, was his answer, and they can achieve it only if they interact socially. In his philosophy of nature, Dante asked what brings about the order of the elements, and suggested that the elements obey the laws of a universal nature in a strictly ordered cosmos. He elaborated all his answers in a scholastic framework that made use of both Aristotelian and Neoplatonic traditions.