Clasificación

On a narrow conception, metaphysics in the Middle Ages was the subject called by that name and directly linked to Aristotle’s Metaphysics. On a wider conception, it includes both that subject and medieval treatments of whatever topics are now considered metaphysical. I shall follow the wider conception here, but very selectively. My aim is to give an impression of the range and complexity of medieval metaphysics, not by setting out themes or positions in the manner of an encyclopaedia, but by looking a little more closely at a few texts or passages. In the fi rst section I shall discuss accounts of the basic constituents of things, before and then after Aristotle’s Metaphysics became current. It will also give the chance to look at the debate over the subject of metaphysics and the relationship between metaphysics and theology. In the second section, I discuss some accounts of non-things – items that seem to fi gure in an ontology, without being considered properly speaking as entities. In the third section, I look at a central issue in the medieval philosophy of time: how is the notion of eternity to be understood?

Two thinkers, Peter Abelard and Thomas Aquinas, act as anchors for these discus-sions. Abelard worked in the period from c. 1100 to 1140, mainly in the Paris schools, at a time when Aristotle’s Metaphysics was still unknown and philosophers were led into metaphysical questions mainly through texts of Aristotelian logic. By contrast, Aquinas, who was working in the 1250s to 1270s, knew the Metaphysics thoroughly, along with the discussions of it in the Arabic tradition.

I have had to exclude far more of medieval metaphysics than I can include. Among the many other areas that particularly deserve treatment are mereology, especially with regard to artefacts (see Henry 1995; Arlig 2005); modality (see Knuuttila 1993); and the “transcendentals” (attributes such as unity, truth and goodness that it was believed every existing thing has; see Gracia 1992; Aertsen 1996).

The basic constituents of things

In the Latin West, Aristotle’s Categories was known (fi rst indirectly, then directly in Boethius’s translation) about four centuries before the Metaphysics started to become

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available. It was from this text, along with the Isagoge (“Introduction”) to it written by the third-century Neoplatonist Porphyry, that philosophers in the early medieval Latin West derived their basic ontology. The Categories makes a distinction between what is

“in a subject” (accidents, nowadays usually called “tropes”) – for example, my whiteness or baldness – and what is “said of a subject” (universals) – for instance, “human being”

is said of me. Particular substances, such as John, are what is neither in a subject nor said of a subject. These divisions correlate with another: of what is signifi ed by all things

“said without combination” into ten categories, the fi rst of which is substance, and the others each sorts of accidents – translating literally from Boethius’s version: quantity, quality, to something (relation), when, where, posture, having, doing and suffering.

Porphyry’s Isagoge regroups these distinctions, by considering the fi ve main types of term that can be used as a predicate: two of them – “genera” and “species” – name classes of universal substances; two – “accident” and “distinguishing accident” (proprium:

an accident that attaches to all and only the members of a certain species, such as ability to laugh for humans) – name classes of accidents. The fi fth, “differentia,” is the essential property that distinguishes species within a genus: in a scheme often repre-sented by medieval logicians as a tree-diagram (“Porphyry’s Tree”), substance was divided by the differentiae corporeality and incorporeality; corporeal substances, i.e.

bodies, were divided into living and nonliving; and so on, until human being – that is to say, corporeal, living, sensibly perceiving, rational and mortal substance – was reached. Human being is a most specifi c species, beneath which there are no other species. A differentia is not a substance; nor is it an accident of any sort, because Porphyry defi nes an accident as that which can come to and go from its subject without the subject’s being destroyed, but it is not even conceivable that something should continue to exist as a substance of a certain sort without any one of its differentiae.

From these two texts, then, by the eleventh century, if not before, philosophers had drawn up a basic metaphysical picture. Every natural thing, apart from God, is either a particular or universal substance or form (that is to say, differentia or accident); artefacts are assemblages of natural things. It was, however, a matter of debate whether there really existed items of all these sorts. Realists held that there also exist particular universal substances forms; nominalists like Abelard held that only particulars – both substances and forms – exist; extreme nominalists, like Abelard’s teacher, Roscelin, seem to have held that only particular substances exist (Marenbon 2004: 27–34, corrected by Marenbon 2008a).

For Abelard, Porphyry’s tree becomes, not a hierarchy of more and less universal classes, but a model for the constitution of particular things. A given human, Socrates for instance, has his or her own particular differentiae of corporeality, being alive, ability to perceive with the senses, rationality and mortality; and there also attach to him or her at any given time a cluster of accidents of various categories, such as whiteness (a quality), being-six-foot-tall (a quantity), wearing-sandals (a having) and writing (a doing). Each of these forms is a real particular thing, though not a substance. Though forms can exist only in a substance, and when an accident leaves one substance, it cannot go on to be in another; they have an individual identity that does not depend on the substances they inform. Socrates might have been made white by the particular

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whiteness that, in fact, makes Plato white. Socrates could not exist without having a form of rationality attached to him, but it might not have been the same form numeri-cally as in fact informs him (Abelard 1919–31: 129, lines 34–6, and 84, lines 19–21; see Marenbon 2008b).

It might seem to follow that there are bare substances, to which differentiae are added to make them into stones, for instance, or roses or humans. But this is not Abelard’s view. Rather, he puts forward two different positions about bodily substances, which are not obviously reconcilable. According to the fi rst, the differentiae attach, not to substance, but to body. After having created primordial bodily matter – an amorphous mixture of the four elements – God then adds to it the differentiae which make it into a particular of some natural kind or another. According to the second, even apart from forms of any kind, substances have an identity as particular members of a species and genus: “even if the forms were removed, things could none the less subsist discrete in their essences, because their individual discreteness [personalis discretio] is not through forms but through the very diversity of essence” (Abelard 1919–31: 13, lines 22–5) (but see Marenbon 2008c King [2004] offers the best account yet of Abelard’s metaphysics).

From roughly the turn of the thirteenth century, Latin translations of Aristotle’s non-logical books, including the Metaphysics, came into use. From the 1250s onwards, all university students (including those who would go on to study theology) followed a curriculum based around Aristotle’s texts. The Metaphysics develops a view of the constitution of things different from that in the Categories, in the context of an inves-tigation into being and into God. The relationship between these two topics was already a matter of dispute in the Arabic tradition, where the Metaphysics had been known since the ninth century. Al-Kindî (c. 801–66) had taken metaphysics, the branch of knowledge as presented by Aristotle, as a way of doing theology to be pitted against the more home-grown Islamic thinkers. Avicenna (Ibn Sînâ, before 980–1037) reacted against this interpretation. He argued that it was in metaphysics that the existence of God was demonstrated. God cannot, therefore, be the subject of metaphysics, because a branch of knowledge must have as its subject matter something the existence of which is already certain. The subject of metaphysics is therefore, he contends, being as being.

Averroes (Ibn Rushd, c. 1126–98) disagreed. He contended that Aristotle proved the existence of God in the Physics, and so God could be the subject of the Metaphysics.

Thirteenth and fourteenth-century Latin thinkers debated the two views, tending to prefer Avicenna’s. But, whichever was chosen, a tight connection – absent in twelfth-century accounts based on the Categories – was made between thinking about the constitution of things and considering the nature of God. A closer look at some of Aquinas’s ideas and their background illustrates this point.

Although substance and accident continued to play a central part in thirteenth-century treatments of how things are constituted, thinkers were led by Aristotle’s Physics, On Generation and Corruption, as well as his Metaphysics, to lay more emphasis on an Aristo-telian idea already known earlier: that each particular natural thing is a composite of matter and form, and that matter is potentiality which form actualizes. The prevalence of this scheme is strikingly illustrated by the model adopted widely to explain human thought about universals. Socrates is matter made actual by an individualized form of

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human; when I grasp the universal, human being, the aspect of my intellect that is in potency acts as the matter to the form of being-a-human, which actualizes it.

Forms were considered to be either accidental or substantial. Although there were many variations in teaching, accidental forms usually were given less ontological independence than in Abelard’s account. For instance, while Aquinas clearly accepts that accidents are real things, distinct from the substances in which they inhere, in some of his discussions, at least, he is ready to admit that they exist only because their subjects exist (Wippel 2000: 253–65). A substantial form was not, as it had been for Abelard, any differentia, but rather that form according to which a particular is the kind of thing it is, and its parts are unifi ed into a whole. It was also envisaged in a more concrete way, as a sort of internal effi cient cause for all the features of a thing that do not come to it from outside – Socrates’s blue eyes, for example, and the fact that he is by birth light-skinned, but not the redness of his eyes the morning after or his designer suntan (Pasnau 2004). Both in its explanatory and causal aspects, and in its variation between individuals of the same species, this conception of substantial form fi tted well with the theory taken from Aristotle’s On the Soul that the soul (or life principle) in living things is the form, to which the body is the matter.

In the Metaphysics, substance is discussed in the wider context of its investigation into what it is to be. This perspective is evident in Aquinas’s On Being and Existence (De ente et essentia, 1252–6). One of the positions he argues against is the universal hylomor-phism that had been advocated by the Jewish philosopher, Solomon ibn Gabirol (d.

1057/8). All things except for God, argued Solomon, even incorporeal ones, are composites of matter and form. By introducing a more fundamental distinction, Aquinas is able to allow some created beings, angels, to be pure forms, without thereby imper-illing the uniqueness of God. In everything, Aquinas, argues – taking a position that many of his fellow theologians would reject – essence and existence are distinct, not merely “by reason” (conceptually), but really. What does he mean by this distinction?

Not the view, sometimes wrongly attributed to Avicenna, that existing is an accident of essence, as if there were many essences and just some happened to exist. Rather (Chapter 4), that not only any form–matter composite, such as a stone or a human, but also an angel, considered by Aquinas to be a pure form, can be grasped mentally without its also being known that any such thing exists. Even, therefore, things in which there is no composition of form and matter are composed of the sort of thing they are, their essence, and existence (esse). The one exception will be that of which the essence is just to exist – and this, Aquinas, argues, is God. Although the relation between form and matter is one of act to potentiality, this does not mean that pure forms, apart from matter, are pure actuality. Even pure forms are themselves in potency to esse itself – that is, to God, who is pure act. They would fail actually to exist were existence not given to them by God. By requiring that the existence of any thing be explained through this activity of pure existing, Aquinas has succeeded in placing God at the basis of his metaphysical analysis of all things. An unorthodox but insightful way of presenting this doctrine (Pasnau 2002: 131–40) is to see Aquinas’s account of things based fundamen-tally not on form and matter, but on degrees of actuality, ranging from the pure potency which is matter to the complete actuality which is God.

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The claim that what God is is just to be can seem puzzling, but it can be read in terms of negative theology: any attempt to specify God as a certain sort of thing is misguided.

The whole basis of Aquinas’s theory of being has been attacked, from a Fregean point, as a confusion (Kenny 2002). But the simple response is that Aquinas’s stand-point is not Frege’s (Klima 2004). It remains true, however, that, despite its greater sophistication, the theological leanings of much later medieval treatment of being and substance make it harder for most philosophers to grasp today than some of the twelfth-century discussions.

Non-things

The Mu^’tazilites, the speculative theologians of early Islam, had a non-Aristotelian conception of accidents, according to which each lasted only for an instant and had to be freshly recreated the next. Tenuous though these accidents’ hold on existence may be, it is far stronger than that of the non-things which appear in different forms in medieval philosophy. The ninth-century thinker, John Scottus Eriugena, begins his masterpiece, the Periphyseon, by dividing nature into what is and what is not. Among the things that are not are those which “through the excellence of their nature escape not only the sense but all intellect.” According to Eriugena, these are not only God, but also the essences or reasons of all things made by him (Scottus 1996–2003: Bk 1, 443AB). It is hardly surprising, then, that Eriugena considers that there are more things in nature than contained in Aristotle’s ten categories, since “none of those who philos-ophize rightly” will deny that possible things and impossible things are counted among things – the impossibles being precisely those which it is impossible should appear to the sense or the intellect (Scottus 1996–2003: Bk 2, 596D–7C).

Eriugena’s negative theology led him to postulate things that lack being. In Abelard’s thinking, and then again, in the fourteenth century, a more rigorously worked out notion of an item that fails to be a proper entity is found. Unlike Eriugena, these philosophers described them explicitly as not being things at all. The metaphysical question was raised by an issue in semantics. Consider a simple sentence such as “It is a rose.” “Rose” signifi es a substance. Does the whole sentence also signify something, and, if so, what sort of entity is it (on the medieval semantics of sentences in general, see Nuchelmans 1973)? Abelard gives a very good reason to think that the sentence must have something it signifi es as a whole, by considering the complex sentence “If it is a rose, it is a fl ower.” This condi-tional, he argues, would always be true, even if there existed no roses and no fl owers, and so there were no entities which the words “rose” and “fl ower” could signify (Abelard 1919–31: 366, lines 6–12). It cannot be that the “if … then …” connection is being asserted simply of the two sentences “It is a rose” and “It is a fl ower,” because the truth of the antecedent of a true conditional requires the truth of the consequent, whereas the fi rst sentence can perfectly well exist without the second one (Abelard 1970: 156, lines 1–21).

Similarly, it cannot be maintained that what the antecedent and the consequent signify are thoughts, since I can perfectly well think “It is a rose” without thinking “It is a fl ower”

(Abelard 1970: 154, line 30, to 155, line 11). There must, then, be some special sort of quasi-entities, distinct from substances or forms of any kind, to which whole sentences

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refer. Abelard calls them dicta, a Latin word which means “the things said.” It is a moot point whether Abelard has in mind truth-bearers – something like propositions in the contemporary sense – or truth-makers, that is to say states of affairs. But he leaves no doubt about the ontological status of these dicta. They are, Abelard insists, not things:

they are “entirely nothing” (Abelard 1919–31: 369, line 1–2).

In denying that dicta are things of any sort, is Abelard incoherently allowing himself to speak as if an item of a certain sort exists while at the same time denying that any such item exists? There seems to be a plausible defence he could make. Since the system of substances, differentiae and accidents accounts for everything about the world (where any substance is at a given time and in exactly what state and relations), a dictum is not some new item: it can be explained completely by these other, genuine things. But there is a problem, because Abelard believes that a dictum such as “It is a rose” requires the dictum “It is a fl ower,” even when none of the objects they concern exists (Marenbon 1997: 207–8; but for a defence of Abelard, see King [2004: 105–8]).

In the fourteenth century, two thinkers Adam of Wodeham (d. 1358) and Gregory of Rimini (d. 1358, too), were led by arguments quite similar to Abelard’s – though they would not have known his work – to posit, as signifi ed by sentences, what they charac-terized as non-things. Their name for them was not dicta, but the more precise complexe signifi cabilia – what are signifi able by a complex (i.e. not a single word but words combined). These signifi ables seem more clearly than Abelard’s dicta to be states of affairs – for instance, that a human being is an animal.

Adam of Wodeham is forced to clarify the ontological status of complexe signifi cabilia by the following objection (Adam of Wodeham 1990: 193, lines 5–8): a signifi able is either something or nothing, but if it is nothing it cannot play the semantic role it was introduced to serve. If it is something, it is either a substance or an accident. But every substance and accident can be signifi ed by a non-complex utterance. So it is purposeless to posit complexe signifi cabilia. Adam answers (Adam of Wodeham 1990: 195) by saying that a complexe signifi cabile such as “that a human being is an animal” is “not a something or a substance,” but it is that a human being is something and that a human being is a substance or an accident. Against the argument that such a signifi able must be something or nothing, Adam suggests that the reasoning is parallel to saying that a people is either a human being or not a human being. So, if it is not not a human being, it is a human

Adam of Wodeham is forced to clarify the ontological status of complexe signifi cabilia by the following objection (Adam of Wodeham 1990: 193, lines 5–8): a signifi able is either something or nothing, but if it is nothing it cannot play the semantic role it was introduced to serve. If it is something, it is either a substance or an accident. But every substance and accident can be signifi ed by a non-complex utterance. So it is purposeless to posit complexe signifi cabilia. Adam answers (Adam of Wodeham 1990: 195) by saying that a complexe signifi cabile such as “that a human being is an animal” is “not a something or a substance,” but it is that a human being is something and that a human being is a substance or an accident. Against the argument that such a signifi able must be something or nothing, Adam suggests that the reasoning is parallel to saying that a people is either a human being or not a human being. So, if it is not not a human being, it is a human