“Common sense” is easy to invoke in everyday life, in philosophy, and in science. However, it is difficult to pin down, for it lies between a familiar chapter in history (see, for example, Peels and van Woudenberg Reference Peels and van Woudenberg2020) and a persistent problem related to our human nature: How can we honor the universal scope of reason while, at the same time, safeguarding the irreducible particularity of sensation without reducing either of them to the other?
In 1939, Étienne Gilson (1884–1978) – a French émigré, Catholic theologian, and proponent of Neo-Thomism – defended the Aristotelian distinction between common sense, a faculty of the sensitive soul, and the common conceptions of reason, epistemic principles of the human intellect (Gilson Reference Gilson and Mark1986). In his Thomist Realism and the Critique of Knowledge, Gilson rejected an anti-Cartesian synthesis of the two that he found troubling. Initiated nearly a century earlier by Jesuit Thomist Matteo Liberatore (1810–1892), this synthesis posited that the “power arising from rational nature, or reason itself, as it spontaneously breaks forth into judgments of this kind in a unanimous way, is called common sense” (Liberatore Reference Liberatore1855, 132; for Gilson’s analysis, see Gilson Reference Gilson and Mark1986, 23–33).
Gilson’s critique of Liberatore combines his concern for metaphysical realism with historiography. While Liberatore had tried to strengthen the firm, universally accepted opinions (κοιναὶ δόξαι) of Aristotle and Thomas Aquinas, Gilson worried that Liberatore had actually combined them with the volatile, rhetorically charged common sense of Cicero, Seneca, and Plutarch. Such syntheses, Gilson judged, “always end in defeat” (Gilson Reference Gilson and Mark1986, 29). This is because they either permit instinct to become the foundation of reason – a solution that the common-sense philosopher Thomas Reid (1710–1796) already suggested before Liberatore – or they are forced to give in to the already existent Aristotelian solution of reason. Historiographically, Gilson asserted that Liberatore succumbed too easily to a Cartesian way of thinking, which did not fully consider that it is the functional connection between sense and reason that is the stronghold of metaphysical realism. Indeed, with his cogito, Descartes moved certainty into the realm of pure thought, deprived sensation of its epistemic power, and reduced the external world to an inference that could only be guaranteed by God Himself. Liberatore’s attempt to combine reason and sense was therefore, in Gilson’s eyes, a way to counter Cartesian skepticism, like that of common-sense philosophy, but it entailed significant downsides.
In what follows, I separate Gilson’s philosophical concern about metaphysical realism from his treatment of its historical development. In the main body of the paper, I focus on the historiographical question, arguing that the historical conditions under which common sense became the epistemic foundation of reason were not limited to theoretical concerns, as Gilson suggests (for the historiographical question, see Rheinberger Reference Rheinberger1997). They were, rather, rooted in the practices of philosophical inquiry and commentary in the long Aristotelian tradition, blending reason with common sense as a practice of philosophical inquiry from the thirteenth century. By concentrating on philosophical practice, I aim to show that Gilson’s critique of Descartes and of the latter’s Thomist opponent Liberatore overlooked an important aspect of the intellectual tradition he was assessing, and I propose instead that the synthesis Gilson rejected was already present within Latin Aristotelian commentaries well before Liberatore.
What this paper traces in historical detail is how sensus communis entered the purview of the conceptiones communes and thereby transformed them in their epistemic value – from the self-evidence of first principles to argued conclusions, to markers of philosophical agreement, and eventually to a topos, a standard of what may be commonly admitted as a ground for reasoning – until sense and reason came to function interchangeably in the Latin commentary tradition. My historical analysis proceeds in two steps, beginning with sensus communis as a power of the sensitive soul and turning to conceptio, assensus, and sensus communis as propositions in philosophical arguments to trace how the first principles of the intellect gradually became demonstrated conclusions and explicit tools of philosophical assent. In so doing, I focus on the Latin commentary tradition developed by Albert the Great (1200–1280), John Duns Scotus (1266–1308), Peter Auriol (1280–1322), Manuel de Góis (1543–1597), and Francisco Suárez (1548–1617). All of these historical actors were also theologians, and the wide circulation of their works meant that their commentary practices reflected and shaped broader epistemic attitudes. I will not discuss the secular arts masters, as my aim here is only to offer a first intervention into the historiography of common sense as a matter of both commentary practice and theory.
By focusing on practice, as is commonly done in the history of science (see, for instance, Erlwein and Krause Reference Erlwein and Krause2025; Daston Reference Daston2007; Rheinberger Reference Rheinberger1997; Knorr Cetina Reference Knorr Cetina1981), and more particularly, by drawing on Yehuda Elkana’s (1934–2012) concept of shifting “images of knowledge,” I aim to study Latin Aristotelian philosophy as a historically evolving scientific practice that uniquely trained philosophical judgment (Elkana Reference Elkana1981; see also Krause and Taylor Reference Krause, Taylor, Krause and Richard2024). Read this way, Gilson’s anti-Cartesian worries become part of a longue-durée history of reasoning practices.
At the end, I revisit Gilson’s philosophical concern about metaphysical realism. Here, I argue that common sense is essential in philosophical practice, but cannot supplant the first principles of reason. For when common sense becomes the sole foundation of human reasoning, reason loses the answerability to truth that it obtains from its contact with reality. And every epistemic practice that forgets this loses sight of the scientific subject, the knower, who is always the condition for any practice to arise.
No middle ground
My history of philosophical practice begins from one part of the dichotomy between common sense and common conceptions in the Latin tradition championed by Gilson: I start with the sensitive soul’s faculty of common sense, leaving aside for a moment the intellect’s conceptiones communes.
“Common sense” (κοινὴ αἴσθησις), as used by Aristotle (384–322 BC), the first to employ the phrase, is an essential faculty or ability through which animals and humans engage in various forms of perception. Aristotle situated the precise workings of common sense in the larger context of his conception of the human soul, in which he took the soul’s activities to be realizations of its different potentialities, whether vegetative, sensitive, or intellectual (Aristotle 1985, 405–406; see also Welsch Reference Welsch1987; Modrak Reference Modrak1989; Everson Reference Everson1999; Jütte Reference Jütte2000; Gregoric Reference Gregoric2007; Johansen Reference Johansen2007). According to Aristotle, who saw the sensitive part of the soul as being shared by animals and humans alike, the different sensory qualities of color and light (vision), sound (hearing), odor (smell), flavor (taste), and tactile attributes such as hot, cold, moist, and dry (touch) are first gathered by the external senses. Common sense then combines them into a single perceptual image. This explanation addressed the question of how humans are able to perceive a single object as a unified whole despite apprehending its different qualities through separate senses. Since only one quality was thought to be the direct object of a given particular external sense, another faculty – common sense – had to combine them into a single object, subsequently storing it and making it available for further cognitive processing in the imagination (phantasia). In addition, Aristotle taught that common sense has its own proper objects, the so-called common sensibles, such as figure, number, and magnitude, which it integrates with the proper sensibles into a coherent object of sensation.
Against this background of the distinctive activities of the sensitive soul, the Greek medical tradition – exemplified by Galen (129–ca. 216 CE) and the Arabic-speaking philosopher-physicians Avicenna (980–1037) and Averroes (1126–1198) – placed new emphasis on the idea that the sensitive faculties had distinct natures and functions in ontological and physiological terms. Galen, Avicenna, and Averroes viewed the faculty of common sense as distinct from the faculty of imagination, and both as distinct from all subsequent faculties of the sensitive soul (Wolfson Reference Wolfson1935a; Jütte Reference Jütte2000, 53–54; Carusi Reference Carusi2002; de Libera Reference de Libera and Cassin2004; Kaukua Reference Kaukua, Silva and Yrjönsuuri2014).
When Aristotle’s works and their accompanying writings were translated from Greek and Arabic into Latin in the late twelfth and thirteenth centuries, many Latin Aristotelians adopted these ideas and began to modify them. Nonetheless, they largely stayed within the narrow frameworks they inherited and initially applied the notion of sensus communis to a faculty of the human soul located in its sensitive part. Following Aristotle and the Arabic philosophers, the Latin Aristotelians viewed the purpose of the sensitive soul as enabling human cognition and facilitating both theoretical and practical knowledge. They divided the sensitive soul into external and internal sense faculties. At times, common sense was not even identified as an internal sense faculty, in part because the Latins inherited a long-standing debate within the Aristotelian tradition regarding the number, kinds, and activities of the internal senses (see Wolfson Reference Wolfson1935a; Steneck Reference Steneck1970, Reference Steneck and Weisheipl1980; Harvey Reference Harvey1975; Kemp Reference Kemp and Wolfgang1997; Tellkamp Reference Tellkamp1999; Lagerlund Reference Lagerlund2007; Di Martino Reference Di Martino2008, Reference Di Martino, Richard and López-Farjeat2016; Knuuttila and Kärkkäinen Reference Knuuttila and Kärkkäinen2008; Wohlman Reference Wohlman2008; Black Reference Black and Adamson2011; Pormann Reference Pormann and Adamson2013; Lisska Reference Lisska2016).Footnote 1
The choices made by Latin Aristotelians in accounting for the nature and activities of common sense were, then, firmly grounded in Aristotelian theories. They largely avoided the epistemic question about common-sense beliefs, what they amount to, or whether they are justified prima facie. Rather, by treating common sense as an undivided faculty located in the brain, the Latins restricted their discussions to its ontological, physiological, and operational scope and purpose, and they never fundamentally questioned human nature’s endowment with this faculty. Common sense was thus regarded as a universal attribute of humanity, present in each individual member of the species.
Even after more than three centuries of Latin commentary practices, the philosophical ideals of the Aristotelian tradition remained crucial for justifying Aristotelian doctrines of common sense as a faculty of the sensitive soul. So deep-rooted were those ideals that they influenced the young René Descartes (1596–1650). Between 1619 and 1628, he aligned his view of common sense with Aristotelian theories in Rule 12 of his Regulae ad directionem ingenii (Descartes Reference Descartes and Wohlers2011, 90–98).Footnote 2
Nonetheless, new and productive questions anticipating more modern discussions of common sense were already present in the Scholastic period, albeit indirectly. A thirteenth-century Franciscan philosopher, Peter John Olivi (1247–1296), stands at the forefront of this development. Following Augustine, he proposed that the faculty of common sense can develop habitual sensitive judgments and discernments as opposed to natural ones. This notion of a habituating common sense raises the possibility of individually directed or focused – and even skilled or trained – operations of common sense, at least at the theoretical level, as Olivi describes:
In his On Music, book VI, Augustine says and proves by experience that some people, from the frequent enjoyment of savoring and tasting wines, acquire a greater skill to judge more easily the fineness or bad quality of wines, or their greater or lesser excellence. And he says similarly that from the exercise of singing and the repeated hearing of a song, an inclination and an acumen arise and are increased to a subtler and easier discernment of the harmonies in the voices, not only in common sense but also in the sense of hearing. (Petrus Iohannis Olivi Reference Olivi and Jansen1922–1926, 2:605)
Olivi can thus be regarded as an early proponent of sense perceptions as individualized, envisioning the faculty of common sense as something that can be shaped and trained in its manifold activities. Apart from Olivi, however, Latin Aristotelian debates on common sense appear to have offered only a narrow discourse around fixed meanings of sensus communis in their explicit deliberations.Footnote 3 By contrast, the shifts emerging from the second part of Gilson’s dichotomy – focusing on the intellect’s conceptiones communes – proved much more fruitful for an early history of the synthesis between reason and common sense.
Objectifying expansions of the conception of conceptiones communes
Over the course of nearly four centuries of Latin Aristotelian thought, the notion of conceptio communis underwent significant changes in meaning. It evolved from denoting the purely theoretical first principles of the intellect only, to referring to the conclusion of a philosophical argument, to a shared body of knowledge among the community of Aristotelian philosophers, and eventually to a shared body of knowledge that was also invoked as “common sense.”
The story of conceptio communis must necessarily start with Anicius Manlius Severinus Boethius (475–526), the first Latin thinker to classify common conceptions as self-evident mental propositions, such as the axiom that the whole is greater than any of its parts.Footnote 4 In the Scholastic period, following the twelfth-century aetas Boethiana (Erismann Reference Erismann and Marenbon2009) and the introduction of Aristotle’s works, Boethius’s conceptiones communes merged with Aristotle’s first principles (prima principia), which reside in the active intellect and are exclusively human.Footnote 5
The Dominican polymath Albert the Great aligned Boethius’s conceptiones communes animi with Aristotle’s first principles of the mind as follows: “As Boethius says, the common conception of the mind [communis animi conceptio] is that which everyone approves upon hearing. And these [conceptions] are those that must be believed, and therefore, they are taken to be the principles [of reason]. And from these other demonstrations are formed” (see, e.g., Albertus Magnus Reference Tummers2015, 12, v. 2–6). Drawing inspiration from his mentor Albert, Thomas Aquinas (1225–1274) limited these first principles to a set of self-evident propositions that inherently include their terms (see Thomas Aquinas Reference Aquinas1992, 269, v. 136–185; Tuninetti Reference Tuninetti1996; Galuzzo Reference Galuzzo2004; Goris Reference Goris2013; Moya Cañas and Miranda Montecinos Reference Moya Cañas and Montecinos2015; Kemple Reference Kemple2017). Aristotelians more generally – including the Arabic philosophers Avicenna and Averroes, whose works were among the conduits for the Latin translations of the Aristotelian corpus – considered these principles to be foundational in an epistemic sense, grounding human knowing upon universal and irrevocably true propositions and definitions.Footnote 6
However, the early fourteenth century marked a pivotal departure from the strict epistemic standards set by Boethius and Aristotle. Universal conceptions were no longer confined to intellectual principles alone but began to encompass empirical and intuitive dimensions as well. John Duns Scotus, the famous Franciscan theologian who studied and taught in Cambridge, Oxford, Paris, and Cologne, significantly broadened the scope of conceptiones communes. He expanded the meaning of common conceptions to include, besides self-evident propositions, those propositions known at present through the senses, such as “the sky is blue,” propositions knowable through experience (per experientiam), such as “the moon is eclipsed,” and propositions referring to our own actions and states, such as “my belly aches” (Duns Scotus Reference Duns Scotus1954, I.3:143, v. 3–7 and I.3:144, v. 11–145, v. 2). Through this epistemic expansion of the self-evident conceptiones communes, Scotus widened the criteria for knowledge to include empirical and self-reflexive factors. The question thus arises: How could Scotus reconcile these empirical conceptiones communes with the purely rational ones to which he also steadfastly adhered?
Peter Auriol, the first Franciscan Scotist philosopher and theologian, who taught theology at Paris between 1318 and 1321, faced a similar dilemma. Like Scotus, Auriol favored broader epistemic criteria for self-evident conceptiones communes over the narrow epistemological and logical ones, and thus extended their scope to embrace both a priori and intuitive a posteriori propositions. Unlike Scotus, however, he excluded self-reflexive propositions from the conceptiones communes, classifying them instead as voluntary intelligibles (voluntarie), intelligibles acquired by the will, following Averroes.Footnote 7
By the early fourteenth century, the explicitly articulated views of conceptiones communes among our historical actors were no longer limited to the deep-rooted first principles imprinted in the human intellectual soul. These conceptions now also encompassed the sensitive soul and experiences arising within it.
Applied expansions of the category of conceptiones communes
These conscious philosophical deliberations were not the only context in which conceptio communis figured in Latin Aristotelian philosophy. Equally – and increasingly over time – the notion of conceptio communis was used as an epistemic tool, a discursive instrument to appeal to shared agreement or common opinion among the community of thinkers. What begins to shift here, to put it into the language of one of Yehuda Elkana’s “images of knowledge,” is the legitimization of knowledge, which transforms in a quiet way the first principles known per se to a consensus among competent commentators (Elkana Reference Elkana1981, 15–16).
As early as the thirteenth century, Latin Aristotelians used the concept of conceptio communis to justify philosophical assumptions. Even the earliest of them, such as Albert the Great, broadened its definition considerably to include general agreement within the community. By applying conceptio communis in this way, Albert also transcended the limits of the strict view of scientia as purely demonstrative.
Albert’s linking of the theoretical and applied meanings of conceptio communis in his commentary practice emerges most clearly in his Metaphysica (ca. 1258). Discussing metaphysics as the science whose epistemic role is to ground the other real sciences (scientiae reales, namely mathematics and natural philosophy), Albert first inquires whether there is just one science that can disclose and verify the principles of demonstration – meaning the “demonstrative common conceptions” – or whether there are many. He unequivocally denies both options, suggesting that, in the narrow technical sense, no conceptio communis can be demonstrated, because it is simply known per se (Albertus Magnus Reference Geyer1960, 114, v. 17–34).
A few paragraphs later, Albert uses conceptio communis again in this technical register to ask whether there is just one science that may study substances and highest beings – and their essential properties and accidents – or many (Albertus Magnus Reference Geyer1960, 115, v. 65–69). He affirms, glossing Aristotle’s view (in the Latin translatio media on which he commented) that the principles of metaphysics are common opinions (opiniones communes), but adds his own much stronger Avicennian view that they are common conceptions of the soul. This reinterpretation of Aristotle’s opinio as conceptio communis marks metaphysics as the primary science, resting on self-evident principles as its unchangeable epistemic pillars.Footnote 8 Later in the Metaphysica, Albert identifies the subject matter of metaphysics with being as being,Footnote 9 but he remains firm in his opinion that conceptiones communes, here taken as first principles of the intellect, ground that science epistemically.
Other appeals to conceptiones communes by Albert, in contrast, were not limited to the narrow technicalities of first intellectual principles known per se. In his natural philosophy, specifically his commentary on Aristotle’s De anima (ca. 1254), Albert included among conceptiones communes both science-specific principles ultimately derived from the first principles known per se and particular conclusions that he had drawn earlier in the same science (Albertus Magnus Reference Stroick1968, 96, v. 26–35). To refute the view that an infinite potency can move in a finite magnitude, Albert appealed to “a common conception of the mind, which was also proven above,” namely “that it cannot happen that an infinite corporeal power exists in a finite magnitude” (Albertus Magnus Reference Hossfeld1995, 644, v. 15–17 and 27–29). As a previously demonstrated conception, this conceptio communis could no longer qualify as a principle of the intellect known per se.
Even more revealing than the demonstrated conceptio communis is Albert’s discussion of the nature and activities of the separate substances, where he further deviates from strong epistemic norms. In his commentary on Aristotle’s Physics, Physica auditu (ca. 1251), for instance, Albert navigates ancient and modern perspectives on the creation of form out of nothing by leveraging the “common conception [conceptio communis] shared by all philosophers” that “nothing simply comes out of nothing” – but he does so only with the aim of refuting this explanation of the creation of a natural form. According to Albert’s own reasoned position, even the highest form, the intellect, requires a certain potency in matter before it comes to establish a new natural substance together with matter (Albertus Magnus Reference Hossfeld1987a, 69, v. 31–70, v. 76).
This broadened view of a common conception as consensus among philosophical authorities can also be found in Albert’s Metaphysica. There, he posits that “it is presupposed by all [philosophers], like a common conception [quasi communis conceptio], that the intellect and the understanding of separate substances are something maximally divine according to the mode of understanding” (Albertus Magnus Reference Geyer1964, 520, v. 26–31). This quasi conceptio communis implied a considerable expansion of common conceptions to include demonstrated and commonly shared propositions. Albert’s practical application of common conceptions as epistemic tools thus did not share identical epistemic standards with his theoretical objectivization of them, at least when it comes to including a wider set of common conceptions that arise in the intellect alone.
This separation of application from objectivization continued into the late sixteenth and early seventeenth centuries, reaching its climax then. In the commentary practices of Manuel de Góis, one of the Jesuit authors of the widely renowned works of the Cursus Conimbricensis, and Francisco Suárez, a leading philosopher and theologian of the School of Salamanca, we find a striking increase in the use of the notion of common conception. In addition, such uses are embedded in a larger, densely intertwined philosophical lexicon, with terms ranging from assensus communis to consensus communis or even sensus communis.Footnote 10 Let me give some examples of this lexicon.
De Góis contributed a commentary on De anima to the Cursus Conimbricensis, a collection of books on Aristotle written by Jesuit scholars for King John III of Portugal in the late sixteenth and early seventeenth centuries. In its question section, which follows the original Greek text, the Renaissance Latin translation by the Greek humanist John Argyropulos (1415–1487), and the lemmatized explanation (explanatio), de Góis repeatedly uses the three notions assensus, consensus, and sensus communis interchangeably to draw his conclusions concerning certain long-disputed questions.
One of the most controversial of those questions, at least since the introduction of Greek and Arabic-language readings of Aristotle’s De anima, was that of the origin of the human soul, and in particular whether the intellectual part of the soul is created by God (see Da Cruz Pontes Reference Da Cruz Pontes1964; Taylor Reference Taylor1982; Seidl Reference Seidl1986; Freudenthal Reference Freudenthal2002, Reference Freudenthal and Hasnawi2011; Carusi Reference Carusi and Viano2005; Genequand Reference Genequand and Hasnawi2011; Krause Reference Krause2015; Silva Reference Silva2015). In the third question of the second book of his De anima, de Góis presents his readers with different assertions that he substantiates with authorities and arguments and assumes the readers will accept – such as that no rational soul is propagated by the power of the semen (first assertion), that it receives its being not by angelic but by divine creation (second assertion), and that it is not created by God before its body but is infused into its body (third assertion). For the third assertion, de Góis invokes the authorities of “doctors who establish by common agreement [assensus communis] that the soul has an inborn inclination to the body, and moreover only attains its perfection while united to the body” (Commentarii [1598] 2013, 57). Common philo-sophical agreement thus served de Góis to substantiate a particular position that was not necessarily shared by the whole community of Aristotelian philosophers throughout the centuries, but certainly by those whom he had identified as being on his side.
Such reference to common agreement is not unique in de Góis’s De anima commentary. In chapter 13 of the third book, he takes up another philosophical debate, this time one concerning the difference between the soul’s faculties of the will and the intellect. Once again, de Góis presents several arguments to corroborate his own conclusion, holding that the two faculties are distinct. Appealing to the common consent of the philosophers, de Góis introduces the counterfactual syllogism that “if the intellect and the will were the same powers of the soul, it would follow that our understanding is by will and our willing by the intellect. Yet by no means does the common consent [consensus communis] of those who philosophize admit of such [a conclusion]” (Commentarii [1598] 2013, 428). In this passage, de Góis is so sure of his case that he does not even list the authorities he has in mind who deny the identity between the intellect and the will.
Even more revealing than the recurrent and seemingly coterminous invocations of assensus or consensus communis within the question sections is the sole use of these notions in another part of de Góis’s De anima commentary, the prooemium.Footnote 11 There, he writes concerning the subject matter of the science of the soul that “every most noble Peripatetic – Simplicius, Philoponus, Alexander, Themistius, Thomas Aquinas, Albert the Great, Giles of Rome, Theophilus, John of Jandun, Cajetan, Silvester Ferrara – and many others obey, by common consent [consensus communis], … and determine the subject matter of these books to be the soul” (Commentarii [1598] 2013, 4). As in the question parts presented before, de Góis invokes consensus communis to collate the many shared views of as many philosophers as possible to prove his point.
Because he does so at the outset of his commentary, the epistemic weight of this use of consensus communis seems to make it an epistemic standard that governs certain understandings of the text in the reader’s mind – always with an eye to the ever-decreasing audience that was still reading these commentaries in Europe. What is more, de Góis’s use of consensus communis here focuses not on the processes that doubtlessly went into reaching the consent, but on the product in which they culminated: the concrete piece of knowledge that is generally agreed upon.
This reading is corroborated by the fact that de Góis subsequently draws apparently quite systematically on these notions of assensus and consensus communis throughout his commentary, even though he never reflects upon their use. His commentary practices, rather than philosophical theory, were what informed the meanings of assensus, consensus, and sensus communis as shared epistemic tools, alongside the Aristotelian theories he discussed and engaged with.
De Góis’s appeals to consensus communis were shared by his Iberian Jesuit contemporaries, especially Francisco Suárez, often regarded as a foundational figure in early modern natural and international law, a moderate Thomist, and a leading figure of the School of Salamanca. Suárez’s commentary on Aristotle’s De anima was published posthumously in 1621. This work alone features more than twenty references (by my count) to common conceptions (conceptiones communes), common opinions (opiniones communes), and common judgments (sententiae communes) – in each case alluding to a shared and established body of knowledge among a centuries-old community of Aristotelians.
For example, on the question of the nature of humans, Suárez concisely sums up four centuries of philosophical debate in the Latin West by mentioning “the common conception of all humans, according to which a human being is essentially a rational animal” (Suárez Reference Suárez and Castellote1978–1991, 1:256, v. 128–129). Before that, however, he had already brushed aside “the common judgment [communis sententia] of all philosophers, nay of all humans,” that the rational soul is “the true soul, and that animals live because they participate in this soul,” by determining that also “the sensitive form is a true soul” (ibid., 1:152, v. 17–20). Suárez also considers it a “common judgment” that the essence of angels is the same as their form, “because the substance of an angel is perfect and complete” (ibid., 1:292, v. 678–680).Footnote 12
But moments of doubt about certain philosophical positions also feature in Suárez’s discussions on the soul, and, perhaps unexpectedly, these positions are subjected to a similar non-technical reference to common conceptions. For instance, when Suárez ponders the long-standing debate between the realists and the nominalists concerning the human act of understanding, he portrays as the “most common” the judgment of the ancients, which holds the “act of understanding to be a separate, real quality distinct from its potency, like an informed species.” According to Suárez, an illustrious community of more than a millennium of philosophers, including Aristotle himself, Philoponus, Themistius, Simplicius, Alexander of Aphrodisias, Galen, Gregory of Nyssa, Nemesius, Thomas Aquinas, John Capreolus, Silvester Ferrara, Cajetan, and Scotus, all endorsed this view. After much consideration of arguments pro and con, including ones of theological provenance, Suárez happily concludes that “the cognitive act is a true quality distinct from the power [of the intellect] and the species” (Suárez Reference Suárez and Castellote1978–1991, 2:342, v. 50–51).Footnote 13
As useful as Suárez’s appeals to conceptiones communes, iudicationes communes, and sententia communia were, they also had their downsides. Their increased scope of reference to a body of knowledge that was no longer absolutely certain but comprised truths accepted by most philosophers diluted the firmness of what were once first principles known per se. First intellectual principles, specific teachings on the science of the soul, shared opinions of the philosophers – all these now constituted epistemic objects under the category of conceptiones communes. But the extended scope of common conceptions and the explicit appeals to them also eliminated a convenient commentary practice of the medieval period: tacit agreement with one’s authorities.
Common conceptions were still intuitively true, but no longer universally shared, which is why their epistemic fate seemed to be sealed. Any skeptical blow, any argument against them, could refute them, because their certainty was vanishing. And yet, for the conceptions presented in Suárez’s De anima, it still seemed true that they were located in the intellect, the faculty he considered immaterial and thus the irrevocable home of universal truths. Why, then, worry, if this was still their locus?
Absorbing sensus communis into conceptiones communes
It seems that the final blow to the conceptiones communes as certain and universally shared propositions came from the Cursus Conimbricensis and Suárez themselves, specifically from their changing lexicon. In a number of instances in de Góis’s De anima commentary, he uses the term sensus communis rather than conceptio communis when referring to the same category of epistemic objects. Suárez’s De anima is no different.
In his discussion of the production of a mental word (verbum mentis) or expressed similitude (species expressa rei), de Góis describes the activity of the human mind as a chain of conclusions in which understanding finally comes to rest. All of these depend upon “the common sense [sensus communis] of the philosophers that every cognition is a kind of assimilation between the cognized object and the cognizer.” But the conclusion that de Góis draws from this common sense is weak; he states only that “it reasonably appears from the fact that cognition arises from an impressed similitude. Hence, it is through cognition that the expressed similitude of a thing is brought forth” (Commentarii [1598] 2013, 485). De Góis’s representation of the mental word in this passage has a distinctly Thomistic ring. Through simple understanding – the first operation of the intellect – humans acquire an impressed species by which they understand. Through judgment and discursive reasoning – the second and third operations of the intellect – they acquire an expressed similitude, a mental word, or a concept. Yet the way this argument is framed no longer has the demonstrative character of Thomas Aquinas’s philosophy. De Góis was aware that an “impressed similitude” was no longer an assured conclusion from the shared premise of assimilation, since by the time of his writing too many rival explanations of mental assimilation were competing with one another. Hence, “it reasonably appears” is all that he could conclude from the premise. A philosophical argument could hardly be weaker.
In his appeal to common sense of the people, Suárez goes a step further than de Góis. He sets aside appeals to uncertain conclusions and instead leans on the normative force of correct conceptual use. In his De anima, Suárez explains that the tripartite division of the soul – vegetative, sensitive, and rational – should not be read as a partition into three fully discrete “complete forms” (formae integrae). Rather, each part is distinguished according to precise concepts, even though one part may be included within the fuller concept of another. On this reading, Suárez can conclude with an explicitly normative verdict: “this is the common sense [sensus communis] of the division, and it shall not be disproved” (Suárez Reference Suárez and Castellote1978–1991, 1:348, v. 305–306).Footnote 14
The irony of Suárez’s move about the tripartition of the human soul is that common sense, in its original Aristotelian meaning, is an ability that resides in the sensitive soul. Its function is to engage in specific kinds of perceptual activity, as explained at the outset of this paper. But Suárez’s appeal to common sense in 1621 had nothing to do with this original meaning, even though the faculty of common sense remained fully operative within his explicit psychological theory. On the contrary, for Suárez, as for de Góis, reason has lost its certainty and, at the same time, has found a new footing in common sense.
Indeed, in their commentary practices, de Góis and Suárez effectively integrate sensus communis with conceptiones communes by using them interchangeably across a broad array of philosophical topics. Two centuries before the Jesuit Liberatore, they blur the distinction between these first principles of the human intellect, introducing into philosophy early instances of what Gilson (Reference Gilson and Mark1986, 32) would later describe as “the most far-reaching and deplorable tendencies.” This blending, occurring primarily in commentary practice rather than in philosophical theories, suggests that even as de Góis and Suárez altered the understanding of the intellectual and sensitive parts of the soul, they might not fully have grasped the implications of their use of these terms. Therefore, it should now be clear that Gilson’s critique, which was initially aimed at the anti-Cartesian Jesuit Liberatore, could likewise be aimed at these two thinkers – a historiographical conclusion that reveals that common sense philosophy originated much earlier in practice than in theory. But why did it matter for Gilson to defend the distinction between reason and sense? And how and why would they need to function together?
Functional connections
What Gilson championed – against what he took to be a fusion of reason and sense in Liberatore – was the preservation of a sound anthropological architecture of knowledge. Within this framework, intellectual first principles and common sense remain distinct poles that function together in an ordered way to ensure that human cognition remains both universal and realist. As a Thomist, Gilson pointed to Thomas Aquinas, who drew on Aristotle, as the prime exponent of this functional unity (Gilson Reference Gilson and Mark1986, 171–194), as he wrote:
what is true of the first principle [of reason] itself [namely being] is equally true of judgments made in light of it concerning every object of sensible perception in general. This is why the senses, the first principle of the content of the first principle [of being], are at the same time the first principle of all real knowledge. We might say that our judgments are made between two extremes: sensation and the intuition of intellectual principles. This is what Aristotle says, and St. Thomas repeats it. (Gilson Reference Gilson and Mark1986, 185)
Gilson’s philosophical claim here is that when “judgments are made between two extremes,” neither of these extremes can be transformed into the other without damaging the realist base of knowledge. To the extent that knowledge arises from sensation, it must maintain a meaningful connection to the particulars; to the extent that knowledge is universal, it must find its ground in principles that cannot be reduced to empirical data or shared consensus. Historically speaking, however, Gilson credits this basis to Thomas Aquinas and Aristotle as his source, whereby Aquinas’s teacher Albert the Great had already lectured his student Aquinas on Aristotle’s ethics in Cologne from 1250–1252. In this, his first commentary on the ethics, Albert already distinguished between sense and reason, and explained in detail how the habit of prudence and the understanding of first principles within the practical intellect are ontologically distinct while functionally united for proper action.
Concerning the difference between prudence and understanding [intelligere], he [i.e. Aristotle] says that understanding is of the extreme terms [extremi termini] in the path of resolution. Of these, there is no reasoning [ratio], no definition, and no syllogism – rather, they themselves are the reasons for other things. Prudence, however, is of the extreme of which there is neither scientia nor understanding, but sensation [sensus]. This sensation is not of proper sensibles in the way that what is proper is divided against what is common (such as colors, sounds, and the like). It is rather of proper things according to which “proper” is said to be essential and to inhere per se. For in this way, the proper object of common sense is the common sensibles, and this sensation is of objects of prudence [prudentialia]. (Albertus Magnus Reference Kübel1987b, 478, v. 6–17)
Albert argues here for a functional interaction between practical reason and its virtue, prudence. While the faculty of the practical intellect is receptive of first principles by its natural inclination, it is also able to cognize singulars in order for its practical judgments to occur. The habit of prudence, however, is not identical with the rational inclination of the practical intellect nor with the faculty itself. Rather, prudence is an acquired virtue and a habit that is perfected by experience and time, and its purpose is to render the faculty of practical reason reliably able to resolve everything to a sensation that is directed at essential and inherent properties in its objects, the so-called prudentialia (Albertus Magnus Reference Kübel1987b, 477, v. 76–84). At a deeper level, this shows how Albert is able to insist on the irreducible difference between the epistemic mode of the first principles of practical reason, the universals, and their actionable particulars. Sensation, including common sensation, can only make the singular available to reason, but it can neither generate reason’s first principles nor bear the normative weight of their universality.
Thomas Aquinas’s later formulation in the Sententia libri Ethicorum (1271–1272) is best read against this background. Just like his teacher, Aquinas distinguishes between prudence and the practical intellect, repeating Albert’s claim that both converge on an extreme: “prudence [prudentia] resembles understanding [intelligere] in the following: [namely] that it is concerned with some extreme” (Thomas Aquinas Reference Aquinas1969, 359, v. 263–265). This picture of collaboration thus shows that Aquinas, like Albert and unlike some of the Aristotelians who succeeded them, did not synthesize reason and common sense ontologically, but rather ordered them functionally in such a way that justification is always based on the first principles. Any development that weakens the stability of these principles will, by necessity, shift the weight toward the common, whether as common sensation or as commonly conceded conceptions.
The later Latin developments, as analyzed in the previous section, must therefore be understood as a clear shift away from this functional interaction between sense and reason, placing an ever-greater emphasis on concepts such as consensus, assensus, and sensus communis. In this way, these philosophers quietly undermined the stability of the first principles of reason and granted increasing epistemic authority to shared agreement among their peers.
Common ground
In this paper, I traced decisive highlights in the commentary practices of the Latin Aristotelian tradition over nearly four centuries and showed how the historical actors gradually ceded to sensus communis the epistemic role of the first principles of reason. In drawing on Yehuda Elkana’s “images of knowledge” I showed how sensus communis entered the purview of the conceptiones communes and thus transformed them in their epistemic authority: from the self-evidence of first principles to the argued evidence of conclusions, to markers of philosophical agreement, and eventually to the uncertainty of topical propositions. My historical study has thus revised the historiography that Étienne Gilson had proposed in his Thomist Realism and the Critique of Knowledge, by identifying the commentary practices of the Aristotelian tradition as an additional historical condition under which Liberatore’s philosophical synthesis of common sense and reason became possible.
However, where Yehuda Elkana’s images of knowledge reach their methodological limits becomes visible in Gilson’s worry that the synthesis of the conceptiones communes with sensus communis in Liberatore amounts to a loss of metaphysical realism. Elkana’s images of knowledge, as well as the more general study of epistemic practices in the history of science, posit that the conditions under which human knowing arises are to be sought in the practices of collectives, gathered at institutions and reliant on material constellations. What carries the explanatory weight of scientific change, in this account, are the observable, historically contingent, and materially constructed practices, and not the way in which a human being’s epistemic ability has been formed through its encounter with reality.
Yet the subject matter at hand, and even more so the concern for metaphysical realism that Gilson holds vis-à-vis Liberatore, reveal that there is a need to question the universal validity of these methodological lenses for our field. For in a historical study of self-referential practices, like our inquiry into the synthesis of sensus communis and conceptiones communes, there is always a subject, who is the ultimate explanans, and who, in reflecting upon their own cognitive activities, turns them into epistemic objects. These activities as objects, however, defy the lens of investigation of observable, historically contingent, and materially constructed practices. For, as unobservable and intellectually conceived objects that aim at a universally truthful description of a self-knowing reality, they are opposed to the very lens through which a historiography of practices proceeds. Admittedly, there are unconscious, or as I have called them here, quiet shifts to these self-referential descriptions and explanations, and many of them are far from epistemically innocent.
This is a fact that becomes particularly visible when these shifts of cognitive practices harden in philosophical theory, as is the case in the writings of Liberatore, where the synthesis of sense and reason is elevated into the very architecture of human rational judgment. When universality is no longer grounded in the nature of the human intellect but secured by appeals to topoi, human reason is no longer answerable to truth that it obtains from its own contact with reality. That this was not yet the case in de Góis and Suárez is what my history of Latin Aristotelianism also shows. For even as explicit appeals to first principles receded in their commentary practices, de Góis and Suárez continued to presuppose these principles as the subject-centered conditions of their reasoning (Erlwein and Krause Reference Erlwein and Krause2025). The anthropological distinction of sense and reason did not vanish from their philosophical theories. It only did so when Liberatore turned what was implicit in their practices into an explicit theory; and at that moment Gilson’s concern finds its justification.
His standard of judgment is not historical – it does not ask for the conditions under which those shifts arose – but metaphysical: whether human reason remains, in its very nature, answerable to the truth of reality. This is the point at which we may wonder about ourselves as historians of science and philosophy. For when the history of science treats practices as the sole explanans, it risks reducing us, too, as its practitioners, to products of the contingent cultural conditions of our time. And yet, to do history at all is already to claim that some descriptions of the past are truer than others. The self-referentiality of the epistemic practices that I discussed in this paper points to more than the practical, institutional, and material conditions under which human knowing arises. For every scientific practice, by definition, is the practice of someone, a human being who carries within themselves the ability to reason, and to do so well once properly trained. Hence, one task of the history of philosophy and science should be to think practice through to its anthropological end.
Acknowledgements
I am deeply grateful to Henryk Anzulewicz, Therese Scarpelli Cory, Lorraine Daston and her Department II of the MPIWG, Steven Harvey, Mogens Lærke, Tony McIlwraith, Rik Peels, René van Woudenberg, and Tracy Wietecha for their invaluable comments and suggestions on earlier drafts of this paper. I also thank the two anonymous reviewers for their generous and insightful feedback, and Kate Sturge and Penelope Krumm for their editorial work on different versions of this manuscript. My work on this study began while I held a Leopoldina Nationale Akademie der Wissenschaften postdoctoral fellowship at Harvard University in the academic year of 2017/2018, whose support I gratefully acknowledge.
Competing interests
none
Katja Krause, a historian of philosophy and science, is Professor of the History of Science at the Technische Universität Berlin and leads the research group “Experience in the Premodern Sciences of Soul and Body” at the Max Planck Institute for the History of Science, Berlin. She also holds a visiting professorship at the Department for Computer Science, Ruhr Universität Bochum, and is an Associated PI at the Lamarr Institute.
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