The title of this presentation, I'm afraid, is a little bit misleading. For this presentation will not, as it cannot, cover the broad topic indicated in the title. Rather, it will concern itself only with some preliminary ideas leading the way to a larger project, which, however, should eventually bear an even broader title. As a matter of fact, here I will consider at some length only two authors from the beginning of the period indicated in the title, namely, Aquinas and Siger of Brabant. (Or perhaps three authors, provided the anonymous author of the Physics-commentary I'll consider is not Siger.) Nevertheless, I think a careful contrast of their views on the issues raised by the conflict between Aristotelian natural necessity and the theology of the Holy Eucharist will bring into focus certain basic conceptual differences within the larger conceptual unity of the period. Indeed, such conceptual differences are especially worth considering if we try to detect those original "hairline cracks" in the 13th-century "cathedral of thought" which later on grew into the ever wider "cracks" and "fissures" that eventually allowed it to be brought down by the series of social and ideological "quakes" of the turbulent late-medieval and early modern period. Obviously, such issues cannot be dealt with in the framework of such a brief presentation, nor am I at this point sufficiently prepared to deal with them. However, in line with the workshop character of this meeting, toward the end of this talk I will risk some working hypotheses concerning these broader issues, to ask for corrections, qualifications, and pointers for my further research in this area.
The conflict between Eucharistic theology and the Aristotelian notion of what is necessary in virtue of a thing's nature is brought to the fore most perspicuously by the following two short passages from Aquinas:
"Praeterea, de eodem praedicatur definitio et definitum. Sed ens per se est definitio vel descriptio substantiae. Si ergo in sacramento altaris accidentia sunt per se non in subiecto, sequitur quod sint substantiae; quod est absurdum." QDL 9, q. 3, obj. 2
"Praeterea, quicumque separat definitionem a definito, ponit duo contradictoria esse simul vera: quia hoc ipsum quod est homo, est animal rationale mortale; et ita si ponatur esse homo et non esse animal rationale mortale, ponitur esse homo et non esse. Sed definitio accidentis est quod inest substantiae; unde etiam in definitione singulorum accidentium oportet quod ponatur substantia. Ergo cum deus non possit facere contradictoria simul esse vera, neque facere poterit quod accidens sit sine substantia." 4SN, d. 12, q. 1, a. 1a, obj. 2
In order that we can fully appreciate the strength of these arguments as well as the replies Aquinas provides to them, we should dwell a little bit on some of their assumptions not quite spelled out in the arguments themselves.
(1) The first, commonly endorsed presupposition is that God cannot make contradictories true. As is well-known, this was understood not to impose any limitation on divine omnipotence, in the sense of not placing any lack of power in God. The nicest illustration of this doctrine I have found in a booklet by Armandus de Bellovisu, one of Aquinas's immediate disciples, entitled Explicationes Terminorum Theologicorum, Philosophicorum et Logicorum. Armandus's example is that just as the fact that a teacher cannot teach a donkey theology does not involve any defect in his teaching abilities, but rather a defect in the donkey's ability to receive knowledge, so the fact that God cannot make contradictories true does not involve any defect in his creative power, but rather a defect in the contradictories' ability to receive being.
(2) The second, also universally accepted assumption is that the quidditative definition of a thing signifies the thing's nature.
(3) The third common assumption is that denying of a thing something that is involved in the thing's quidditative definition results in a contradiction. Clearly, this assumption, along with the previous one, entails that when we talk about natural necessity in this context, what is meant is not some weaker-than-logical, causal necessity (in the sense in which natural necessity is commonly contrasted with logical necessity in modern philosophy). What is naturally necessary in the sense relevant here, that is, in the sense that it is necessary on the basis of what is involved in the thing's nature, is necessary in such a manner that its opposite would be logically contradictory, and hence, in virtue of the first assumption, impossible to realize even by divine power.
(4) The fourth assumption is that "something which is in a subject" [quod est in subjecto], or some equivalent formulation [such as ens in alio], is the quidditative definition of an accident, or at least a description having the force of a quidditative definition, based on what Aristotle says at the beginning of his Categories.
Now these assumptions obviously entail that the claim that an accident exists without a subject is contradictory, and hence that it cannot be made true even by divine power. But this conclusion would mean that the miracle of the Holy Eucharist would be impossible; therefore, one of these assumptions has to be discarded. However, none of these assumptions is easily dismissible. Eliminating the first would go directly against the first principle, the principle of non-contradiction. Rejecting the second would be contrary to what is meant by a quidditative definition. Denial of the third would again be contrary to what it means to have something involved in the thing's quidditative definition. And finally, rejecting the fourth would seem to undermine the very point of the Aristotelian distinction between substance and accident.
Yet, Aquinas's reply takes aim at this last assumption. In his reply to the objection of the Quodlibeta he first points out that the usual way of quoting the definition of accident is in conflict with Avicenna's conclusion, according to which the existence of a thing cannot figure in its definition. Then, on the basis of this observation, he moves on to show what should be regarded as the correct interpretation of the definition of substance, and, correspondingly, that of accident. Finally, he points out that with this understanding of the definition of accident there is no contradiction involved in the claim that an accident miraculously exists without a subject:
"Ad secundum dicendum, quod secundum Avicennam in sua Metaph., esse non potest poni in definitione alicuius generis et speciei, quia omnia particularia uniuntur in definitione generis vel speciei, cum tamen genus vel species non sit secundum unum esse in omnibus. Et ideo haec non est vera definitio substantiae: substantia est quod per se est; vel: accidens est quod est in alio. Sed est circumlocutio verae descriptionis, quae talis intelligitur: substantia est res cuius naturae debetur esse non in alio; accidens vero est res, cuius naturae debetur esse in alio. Unde patet quod, quamvis accidens miraculose sit non in subiecto, non tamen pertinet ad definitionem substantiae; non enim per hoc eius naturae debetur esse non in alio; nec egreditur definitionem accidentis, quia adhuc natura eius remanet talis ut ei debeatur esse in alio." QDL 9, q. 3, ad 2-um
The same point is made in somewhat more detail in the reply to the objection in the commentary on the Sentences.
"Ad secundum dicendum, quod sicut probat Avicenna in sua Metaph., per se existere non est definitio substantiae: quia per hoc non demonstratur quidditas ejus, sed ejus esse; et sua quidditas non est suum esse; alias non posset esse genus: quia esse non potest esse commune per modum generis, cum singula contenta in genere differant secundum esse; sed definitio, vel quasi definitio, substantiae est res habens quidditatem, cui acquiritur esse, vel debetur, ut non in alio; et similiter esse in subjecto non est definitio accidentis, sed e contrario res cui debetur esse in alio; et hoc nunquam separatur ab aliquo accidente, nec separari potest: quia illi rei quae est accidens, secundum rationem suae quidditatis semper debetur esse in alio. Sed potest esse quod illud quod debetur alicui secundum rationem suae quidditatis, ei virtute divina agente non conveniat; et sic patet quod facere accidens esse sine substantia, non est separare definitionem a definito; et si aliquando hoc dicatur definitio accidentis, praedicto modo intelligenda est definitio dicta: quia aliquando ab auctoribus definitiones ponuntur causa brevitatis non secundum debitum ordinem, sed tanguntur illa ex quibus potest accipi definitio." 4SN, d. 12, q. 1, a. 1a, ad 2-um
Again, there are a number of points in these two passages that must not escape our attention if we want to understand properly the significance of Aquinas's solution.
First of all, St. Thomas does not reject here any of the philosophical assumptions listed above exclusively on the basis of the conflict between the claim they entail and an unquestionable theological conclusion. Rather, this conclusion only signals for him that there must be something wrong with at least one of these assumptions, whence it has to be revised in the light of further careful, philosophical analysis. (This is a point I dwelled on at some length in my paper presented in Erfurt, comparing in detail the respective methodologies involved in Aquinas's and the Latin Averroists' handling of such conflicts.)
The philosophical analysis in question is provided by Avicenna, a physician and philosopher, and an outstanding Aristotelian authority. (To be sure, it has to be added here that Siger in his commentary on the Metaphysics, when he considers Avicenna's relevant arguments, quite flatly states that the authority of Avicenna should not be given credence here, since his position is based on error.) The details of the Avicennean argument indicated by Thomas are difficult to interpret, but the gist of the idea seems to be quite clear. Suppose that what the term `substance' signifies, the quiddity of substance, is the same as what the term `being' signifies in all substances. Then the term `substance' would be common to all substances in the same way as the term `being' is. However, since `being' cannot be a genus, in that case `substance' would not be a genus either, which is false. Hence, if all the other premises are true, then we have to reject the initial assumption, namely, that what the term `substance' signifies, the quiddity of substance, is the same as what the term `being' signifies in all substances.
The only questionable premise, namely, that `being' is not a genus, is briefly justified by the following consideration. A generic term signifies something that is common to all individuals that fall under it. But the term `being' signifies not what is common to all individuals that fall under it, but it signifies precisely that on account of which they differ from one another, namely, their being. Therefore, the term `being' cannot be common to all these individuals in the way a genus is.
Well, perhaps, one might have qualms about this argument to the effect that according to Aquinas a genus does not signify one common thing any more than the term `being' does, and so the alleged difference -- namely, that while the genus signifies something common to all its inferiors, the term `being' signifies something that distinguishes these inferiors -- cannot serve to establish the distinctness of what they signify. But perhaps we can quickly allay such worries by pointing out that even though what the genus signifies is not one common thing, but rather the individualized natures of the things that fall under it, nevertheless, these things, insofar as they fall under the genus do not differ from one another on account of these individualized natures. On the contrary, the individualized natures signified in the individuals by the genus are precisely the reason why all these individuals fall under the same genus. On the other hand, given the convertibility of one and being, these individuals are individuals distinct from one another precisely on account of the fact that they have distinct acts of being, and these distinct acts are precisely what is signified in them by the term ens.
In any case, whether or not the argument as presented here is conclusive sub specie aeternitatis, its conclusion certainly allows a more sophisticated analysis of the usual formula of the definition or quasi-definition of accident. For if what the definition of an entity signifies is one thing, and what the term ens signifies in the same entity is another, then a formula containing ens in place of the generic term of a definition cannot be regarded as a definition signifying the quiddity of this entity. Consequently, it is wrong to construe the quasi-definitions of substance and accident, namely, ens per se and ens in alio, respectively, as consisting of the quasi-generic term ens, and the quasi-differences per se and in alio. But it is only this understanding of these formulae which would allow the objections to the doctrine of the holy Eucharist to proceed, for it is only this understanding of these formulae which would entail that an accident without a subject would have to be an entity which lacks something from its quiddity, namely, an inherent act of being (esse inhaerens), the act of being in a subject.
So the point of Aquinas's rejection of our fourth assumption above is that the usual formula, or any equivalent formulation, cannot be taken as a quidditative definition of accident, provided it is interpreted as signifying the act of being of accidents, and specifying what kind of act it is. His reason for this rejection is not the conflict with a theological doctrine that would otherwise emerge, but the general Avicennean consideration concerning quidditative definitions, according to which such definitions cannot signify (by their quasi-generic term) and specify (by their quasi-difference) the kind of act of being that the entity to which such a definition applies is supposed to have.
But this solution is obviously incomplete until one tells what, then, the correct definition of accident is, or rather, what the proper understanding of the usual formula should be. What Aquinas provides here as an answer is in perfect agreement with the requirement that a quidditative definition should signify the quiddity of the thing defined (that is to say, of the thing to which the definition applies). He says that ens in alio should be interpreted as signifying a thing which by its nature demands an act of being in something else. Obviously, in this reply everything hinges on how we understand the phrase res cui debetur esse in alio, which, taking into consideration its context as well, I translated in my previous sentence as `a thing which by its nature demands an act of being in something else'. The crucial question here, therefore, is how we should understand the possibility that a thing can lack something demanded by its nature, as opposed to the impossibility and self-contradiction that a thing could lack something from its nature.
As is usually the case with difficult metaphysical questions, a relatively well-understood, mundane example can be helpful here in clarifying the relevant conceptual relationships. One such example is provided by what Aquinas says about how the nature of heavy bodies demands that they should be down, that is, near the center of the universe, which, nevertheless, does not mean that it would entail a contradiction for a heavy body to be up, that is, removed from the center. As he writes:
"Nihil enim prohibet aliquid non habere in sua natura causam alicuius, quod tamen habet illud ex alia causa: sicut grave non habet ex sua natura quod sit sursum, tamen grave esse sursum, non includit contradictionem; sed grave esse sursum secundum suam naturam contradictionem includeret." De Unitate Intellectus , c. 5
So, for a heavy body to be up is not incompatible with its nature. What would be incompatible in this way would be for the heavy body to lack from its nature the disposition to be down, when nothing forces it to be up. Clearly, when something that is involved in the nature of the thing is merely dispositional, then there is no contradiction involved in the fact that a powerful external agent can overcome this natural disposition, and can force the thing in question to be in a way in which it would not be, were it not for the contrary action of this agent:
"Quod autem aliquid deficiat a sua naturali et debita dispositione, non potest provenire nisi ex aliqua causa trahente rem extra suam dispositionem, non enim grave movetur sursum nisi ab aliquo impellente, nec agens deficit in sua actione nisi propter aliquod impedimentum." ST1 q. 49, a. 1.
So a powerful agent can overcome what is dictated by the thing's natural disposition in that it may force the thing to have an actual property which without the influence of the agent it would not have. However, if the disposition itself is involved in the thing's nature so that eliminating that disposition would destroy the thing's nature, then this disposition is inseparable from the thing, even by an infinite power; for the separation in the sense that the thing would still exist while its nature is destroyed would involve the contradiction that the thing should both exist and not exist, since the destruction of the thing's nature is nothing but the destruction of the thing itself.
Now applying these considerations to the case of the accidents maintained by divine power without their subjects, we can explicate St. Thomas's solution in the following manner. When the substance of the bread is converted into the body of Christ, and thereby it ceases to be the subject of its accidents, the accidents can be maintained in their existence by divine power in pretty much the same way as heavy bodies can be kept in place by a force pulling them upwards even when they lose their support, as for example the roof of a house could be kept up in the air by a helicopter even if the walls that supported the roof were destroyed by an earthquake. Clearly, such a situation would not entail any contradiction whatsoever. The roof would not cease to be a heavy body, and thus it would still preserve its natural disposition to fall when it is unsupported, even if it actually does not fall, because of the force keeping it from following what is demanded by this disposition. Indeed, that it did not lose this disposition is clearly demonstrated by the fact that it still needs the force to keep it from falling: had it lost this disposition, it would not need the force to keep it from falling, for to have this disposition is precisely to behave in the way demanded by the disposition, provided that nothing interferes, and thus not to have it is not to behave in the way demanded by the disposition, even when nothing interferes.
But the same goes for the accidents without their subject in the miracle. Given the fact that they are accidents, they have a nature that involves a disposition demanding that they should exist in a subject. Therefore, anything that would take away that disposition would destroy that nature, and thus the accident itself, whence to posit an accident in being without that natural disposition would be to posit contradictories. However, this does not mean that the accident cannot be preserved in its being, leaving that natural disposition intact and yet without the actual realization of what that disposition demands, given the fact that the actual demand of that disposition can be overcome by a greater power.
There are, therefore, two crucial points in Aquinas's solution. The first is a negative point, stating that the usual definitional formula is not to be understood as defining what kind of entities accidents are in terms of specifying what sort of act of being such kind of entities must actually have. The other is an affirmative point, which states that the customary formula should be understood as defining accidents by specifying their nature in terms of a disposition which demands a certain kind of being. To have that disposition involved in the nature of thing, however, means only that if nothing interferes with the natural operation of the thing, then the thing will have what is demanded by that disposition, namely, an inherent act of being. But this is not incompatible with the case when there is a powerful agent that does interfere with the natural operation of the thing and provides it with a non-inherent act of being.
Now if we turn to the relevant passage from the anonymous Physics-commentary, we find the exact opposite position:
"Ad tertium dicendum, quod deus potest omne, quod habet rationem possibilis simpliciter. Est autem possibile de aliquo solum quod non est contrarium suae rationi. Cum ergo non esse in subiecto sit contrarium rationi accidentis, non habet rationem possibilis, sed impossibilis contradictionem implicantis, cum ratio accidentis secundum Philosophum sit non tantum, ut aptum natum sit esse in subiecto, sed ut sit in subiecto."
The author here obviously rejects both what I identified as the negative and what I identified as the affirmative points of St. Thomas's solution. On the one hand, he denies that what belongs in the nature of an accident would be simply an aptitude, a disposition to have an inherent act of being. On the other hand, he asserts that to be in a subject belongs to the ratio of accident, which amounts to the claim that what is signified by the definition of accident specifies precisely the kind of esse an accident has to have, namely, an act of inherent being, esse in subiecto.
This denial of Aquinas's solution would then lead us back to the original problem, namely, the apparent impossibility of the miracle. The next sentence, however, does concede some sort of inexplicable possibility for the miracle, to be held by faith alone.
Nec apparet aliqua, quae aliquando sunt in subiecto, aliquando exsistere sine subiecto lumine rationis naturalis, licet per miraculum credendum sit hoc posse fieri.
Nevertheless, the author simply does not tell us whether there is a resolution of the contradiction resulting from his position, and if so, what that resolution would be, or whether perhaps we should hold the possibility of the miracle by faith despite the (alleged) fact that it involves an irresoluble contradiction.
The next step in the author's argument is to deny the principle that serves as the basis for upholding the possibility of the miracle, once it is assumed that for an accident to exist without a subject does not involve a contradiction, namely the principle that whatever a superior agent can produce with the cooperation of an inferior agent, it can produce also without this cooperation:
Substantia enim est causa materialis accidentis, et hoc modo deus non <est> causa accidentis Non oportet autem, si deus potest facere aliquem effectum mediante eius causa, causa aliqua, quae est illius forma vel materia, quod possit illum effectum facere per se. Tunc enim contingeret, quod exsistentia solius dei exsisterent omnia entia in propriis eorum naturis et secundum eorum proprias rationes. Non oportet etiam, quod illud, quod potest causa primaria efficiens mediante secundaria efficiente, quod illud possit sine secundaria, eo quod effectus non fit sine causa ad effectum illum determinata potius quam ad oppositum. Primaria autem sic per secundarias determinatur.
In the authentic commentary of Siger of Brabant on the Liber de Causis we find the same rejection:
"Unde sophistice quidam arguunt credentes naturali ratione ostendere et demonstrare quod causa prima possit facere quod accidens existat sine subiecto illius accidentis, propter hoc quod causa prima est causa omnium causarum mediarum accidentis inter ipsam et accidens, et ideo sola facere possit quod existat accidens, quamquam accidenti nulla existat aliarum causarum accidentis; et cum substantia sit aliqua causa accidentis, poterit facere ut sine substantia subsistat accidens. Ratio, ut manifeste apparet, deficit secundum ea quae prius dicta sunt. Ut tamen sane intelligatur, sciendum est quod primariam causam posse facere accidens existere sine subiecto illius accidentis confitemur. Hoc tamen est non propter istam rationem: est enim oratio conclusa peior seipsa non conclusa."
But in this text Siger does not go as far as to claim the contradictoriness of the assumption that an accident should exist without a subject. All he denies here is the principle concerning the hierarchy of agents. Accordingly, he does not deal here with the issue of whether the definition of accidents involves the type of being they should have, and whether on account of this it would be contradictory for an accident to exist without a subject, as the author of the Physics-commentary explicitly states.
However, we do have some evidence that this would quite fairly characterize Siger's view on the matter. In his commentary on the Metaphysics, after vehemently denying the thesis of the real distinction between essence and existence in the creatures as stemming from an error of Avicenna's, he insists in his reply to one of Aquinas's arguments for the real distinction that esse need not multiply in beings because of something added to it, but rather it is multiplied on account of its ratio essendi, the diversity of which in different kinds of beings is entailed by Aristotle's claim that ens cannot be a genus. However, in the question directly addressing this latter issue, he explicitly concludes that the reason why ens cannot be a genus is that the ratio essendi of accidents, being a non-absolute ratio, cannot be the same as the ratio essendi of substances, which is an absolute ratio. In a different context -- most notably in the context of the question whether the intellect can be both subsistent and inherent -- he also insists that these rationes essendi are so incompatible, that they cannot belong to the same thing. But also in the context where he directly addresses the question of what sort of quiddity accidents have, he explicitly asserts: "accidens non habet rationem essendi nisi in habitudine ad substantiam, et ideo definiri non potest sine substantia". Now the implication of this, along with Siger's previous identification of essence with existence, is clearly that the same thing, while remaining the same thing, cannot have one ratio essendi after the other, and thus, an accident, having the ratio essendi of an inherent being, cannot, while remaining what it was, an accident, have later on the ratio essendi of a subsistent being, on pain of contradiction.
But even without going into the further details of Siger's position, I think the foregoing considerations allow us to draw some general conclusions, which give rise to a number of interesting questions in the broader context of this inquiry.
First of all, as from the analysis of Aquinas's solution and from the anonymous Physics-commentary's rejection of this type of solution it became clear, the way an author handles the problem generated by the requirement of positing the miraculous non-inherent existence of accidents is primarily dependent on his conception of what the Aristotelian description of accidents signifies. To be sure, the issue here is clearly not a matter of mere semantics. For the question is not whether by a clever reinterpretation of our terms we can turn an originally contradictory claim into a non-contradictory one. The question rather is whether in keeping with the original intention of the Aristotelian description one is forced to conclude that attributing non-inherent existence to accidents is contradictory or not.
But then this naturally leads to the further question whether the original Aristotelian intention should be interpreted as defining accidents in terms of specifying the kind of act of being these entities have, or rather as defining them in terms of their nature, which, being the kind of nature it is, demands inherent existence. And it is at this point that the question will directly attach to the general problem of the real distinction between essence and existence. For given that a quidditative definition signifies the essence of the thing defined, the question in fact is whether the significatum of the definition in this thing will be the same as, or distinct from, what the term `ens' or `esse' signifies in the same thing, and thus whether the definition directly provides a specification of the kind of esse the thing has, or rather only a specification of the thing's nature, which then would further determine the kind of esse it requires.
Furthermore, through these considerations the issue is also closely related to the question of the analogy vs. univocity of being. In any case, from Siger's discussion in the Metaphysics-commentary it seems to be quite clear that he regards the difference between the rationes essendi of substance and accident as the ultimate foundation of the claim that the notion of being is analogous, whence it cannot be a genus.
By contrast, if one were to allow that the esse of an accident is an act of being in the same sense as the act of being of a substance is, regardless of whether the accident actually inheres or not, then the contradiction would not even pose a threat, for then the miracle would simply consist in "detaching", as it were, the relation of actual inherence from the accident in question, while maintaining its unchanged being in its unchanged nature (which actually may be the same thing), since this unchanged nature accounts only for the aptitude to have this relation or mode of inherence "attached" to it, if no greater power "detaches" it.
Now this seems to be Scotus's approach to the matter. As we could see, in the Metaphysics-commentary Siger established the accidents' absolute dependence on substance on the basis of rejecting what he took to be Avicenna's error in interpreting Aristotle. On the other hand, it was precisely Avicenna's "essentialism" that allowed Thomas to interpret this dependence in terms of an aptitude to inhere rather than in terms of actual inherence. But Aquinas's solution is also radically dependent on his thesis of the real distinction and on his doctrine of the analogy of being, both of which are rejected by Scotus.
So an interesting historical-hermeneutical question stemming from these considerations is the following: exactly how could this new type of solution emerge? What conceptual changes took place between Thomas's and Scotus's time that allowed such a radical reinterpretation of the fundamental Aristotelian distinction between substance and accident?
I think it is clear that we can learn a great deal concerning how Scotus's approach emerged from a further careful study of these issues in the works of such "intermediary" figures as for example Giles of Rome or Henry of Ghent, both of whom seem to have moved in the direction of identifying accidents with their act of being, while treating their inherence as an attached modus, which can easily be "detached" by divine power.
But the further, really intriguing lessons we may learn from such investigations concern the broader issues I indicated at the beginning of this talk. For what is really interesting in the apparently ever greater "autonomy" that accidents seem to have gained in the discussions of the theologians of the late 13th and early 14th centuries is that the semantics of the discourse concerning these easily "detachable" accidents is very much like the semantics of the discourse concerning simple substances. But this, it would appear, might provide a perfectly good motivation for attempts to simplify the semantics of discourse concerning all mundane entities along these lines, thereby directly pointing the way toward the great "semantic schism" of the later middle ages, caused by the emergence of 14th-century nominalism.
 Armandus de Bellovisu: Explicationes Terminorum Theologicorum, Philosophicorum et Logicorum, Wittebergae, 1623, p. 28: "... et illud quod non potest facere dicitur impossibile, non propter defectum divinae potentiae, sed propter defectum rei factibilis quae non est capax. Sicut magister in theologia de potentia absoluta potest docere theologiam, sed quod non possit docere asinum non est defectus potentiae in magistro, sed est defectus asini, qui non est capax doctrinae."
 "Ad auctoritatem Avicennae dicitur quod non est ei credendum quoniam erravit." Siger de Brabant: Quaestiones in Metaphysicam, (ed. A. Maurer), Louvain-la-Neuve: Éditions de l'Institute Supérieur de philosophie, 1983, Introductio, q. 7, p.35.
 Ein Kommentar zur Physik des Aristoteles aus der Pariser Artistenfakultat um 1273, ed. A. Zimmermann, Berlin: De Gruyter, 1968, p. 25.
 Les Quaestiones super Librum de Causis de Siger de Brabant, ed. Marsala, A., Publications Universitaires: Louvain, Béatrice-Nauwelaerts: Paris, 1972, p. 41.
 Siger de Brabant: Quaestiones in Metaphysicam, (ed. A. Maurer), Louvain-la-Neuve: Éditions de l'Institute Supérieur de philosophie, 1983, Introductio, q. 7, p. 34, ll. 30-40.
 "Ad aliud, quod similiter fuit medium Thomae (ScG, II, 52), dicitur quod esse per se subsistens, quod est maxime proprie esse et actualissimum, illud est unum tantum, scilicet Esse Primum. Esse tamen posterius et causatuum, quod accedit ad naturam potentiae, non est unum sed plura, secundum quod sunt plura entia causata. Et tu arguis quod esse illud, secundum quod esse est, non est multiplicatum; ergo multiplicatur per aliquid cuius est esse illud. Et dicendum quod bene argueres si esse in omnibus entibus causatis esset unius rationis: tunc enim non multiplicaretur nisi per aliquid additum sibi. Nunc autem non est unius rationis in omnibus entibus. Et ideo ex sola multiplicatione rationis essendi multiplicatur esse in entibus. Nec potest ratio essendi multiplicari per aliquam rationem sibi additam, quia non est aliqua ratio sibi addita. Omnis enim ratio est essendi ratio. Ex hoc enim probat Aristoteles IIIo hujus quod ens non potest esse genus." Ibid. pp. 36-37.
 "Dico ad hoc quod ens non significat aliquam rationem unam contractam ad substantiam et ad accidentia, sed significat rationem diversam in substantia et accidentibus. Quod probatur sic. Omnis enim ratio quam significat aliquod nomen vel est ratio absolute dicta, vel est ratio dicta per ordinem ad aliud, quia nulla potest esse his communis. Si igitur ens significet aliquam rationem unam in substantia et accidentibus, vel illa erit ratio absolute dicta vel erit ratio dicta per habitudinem ad aliud. Si primo modo, tunc ens non praedicabitur de accidente, cum accidentis non sit ratio essendi absolute dicta. Si secundo modo, tunc ens non praedicabitur de substantia, cum substantiae non sit ratio essendi dicta per habitudinem ad aliud. Relinquitur igitur quod ens non significet aliquam rationem unam in substantia et accidentibus." Ibid. lb 33, q. 12, p. 101.
 "Praeterea, alia est ratio essendi formae materialis et compositi seu formae per se subsistentis. Ratio enim essendi formae materialis est secundum quam est aliquid aliud, ut ratio compositionis est secundum quam habet esse compositum, et ratio figurae secundum quam habet esse figuratum unde ratio essendi formae materialis est quod sit unita alii. Ratio autem essendi compositi vel formae liberatae a materia est quod sit ens per se et separate, non unum ens cum alio. ... Et sunt istae rationes essendi, qua aliquid habet esse unite ad materiam et qua aliquid habet rationem subsistentis per se et separate, oppositae adeo ut eidem inesse non possunt. Unde anima intellectiva non potest habere rationem per se subsistentis et, cum hoc, unum facere cum materia et corpore in essendo." Siger of Brabant: De Anima Intellectiva, in: Bazán, B.: Siger de Brabant, Louvain-Paris, 1972, pp. 79-80. Cf. also St. Thomas's De Unitate Intellectus nn. 37-38.
 Siger de Brabant: Quaestiones in Metaphysicam, (ed. A. Maurer), Louvain-la-Neuve: Éditions de l'Institute Supérieur de philosophie, 1983, lb. 7, q. 10, p. 341.
 Cf. text in n. 8.
 In any case, this is the conception of the inherence of accidents he advances in his Metaphysics-commentary. Joannis Duns Scoti Opera Omnia, t. 7, Quaestiones subtilissimae super libros Metaphysicorum Aristotelis, Parisiis, apud Ludovicum Vivès, 1893, lb. 7, q, 1, pp. 350-355.