Kenny Anthony. Medieval Philosophy: A New History of Western Philosophy. Volume 2
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truly predicated of many things. Here there are two possible cases. The
concept heptagonal house, he tells us, is not truly predicated of anything, but
there is nothing to stop that universal being instantiated many times. The
concept sun, however, is truly predicated of only one thing, and ca nnot be
truly predicated of more than one thing; but this impossibility, he says, is a
matter of physics, not of logic. Individuals are quite diVerent. ‘An individ-
ual is something that cannot be conceived as being predicated of more than
one thing, like the essence of Zayd here, which cannot be conceived as
belonging to anything other than himself’ (Metaph. 5. 196).
Consider the concept horse. We can consider this in three ways: we can
consider it as it has being in individuals, or in respect of the being it has in
the mind, or we can consider it absolutely, in the abstract, without
reference to either being.
The deWnition of horseness bypasses the deWnition of universal, and universality is not
contained in the deWnition of horseness. Horseness has a deWnition which has no
need of universality; universality is something extra. Horseness is itself nothing but
horseness; in itself it is neither one nor many, in itself it does not exist either in
perceptible individuals nor in the soul . . . Horseness is common, in that many
things share its deWnition; but if you take it with particular properties and
designated accidents, it is individual. But horseness in itself is nothing but horse-
ness. (Metaph. 5. 196)
Avicenna is not saying, in Platonic style, that there exists such a thing as
horseness in itself, apart from any individual horse. Horseness is something
that occurs in individual horses, Bellerophon or Eclipse, and we can study
it by examining it in these individuals. We can consider also the concept as
it occurs in the mind: as when we say that the concept horse is a concept
easily attained. But we can also consider in the abstract what is involved in
being a horse, and this is considering horseness in itself (Metaph. 5. 207).
Horseness in an individual horse, and humanity in a particular human,
will be accompanied by ‘particular properties and designated accidents’,
Avicenna says. For Aristotle, it would be these designated accidents—the
ones that mark out a particular parcel of matter—that would be what
individuated Socrates. But for Avicenna the humanity in an individual
human is itself individuated. Though the humanity of Zayd and the
humanity of Amr do not diVer from each other, it is quite wrong to
think that they are numerically the same: they are not one but two
humanities. For Avicenna, there are individual as well as generic essences.
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The invention of individual essences holds out the possibility of the
individuation of non-existent entities. Just as the coming into existence of
steam out of water can be looked on as the addition of the form of steam to
the pre-existent matter that was previously water, so the coming into being
of Socrates can be looked upon as the addition of existence to an essence
that previously lacked it. The pre-existent essence can be regarded as a
potentiality whose actuality is existence. Thus essence and existence appear
as a third potentiality–actuality pair alongside matter–form and sub-
stance–accident. Existence, Avicenna sometimes seems to say, is an acci-
dent added to essence.3
In the case of a being that is necessary of itself, there is no question of
having being after non-being, and so the distinction between essence and
existence does not arise. But in all other entities, on Avicenna’s view, the
two are distinct. Since Avicenna’s time some philosophers have agreed that
in all cases except that of God there is a real distinction between essence
and existence; other philosophers have denied this, but all have treated the
issue as important. But the signiWcance of the issue depends on whether, in
this context, ‘essence’ means generic essence or individual essence.
If we take ‘essence’ in the generic sense, then the distinction between
existence and essence corresponds to the distinction between the question
‘Are there Xs?’ and ‘What are Xs?’ That there are quarks is not at all the
same thing as what quarks are. If this is what the distinction amounts to,
then it is undeniable.4 But if we take the distinction to be one about
individual essences, then it seems to entail the possibility of individual
essences not united to any existence; individual essences of possible, but
non-existent individuals. The essence of Adam, say, is there from all
eternity; when God creates Adam, he confers actuality on this already
present potentiality.
The postulation of individual essences, though it was to be inXuential
down to the present day, was a recipe for philosophical confusion. Let us
ask how an individual humanity—say the humanity of Abraham—is itself
individuated. It is not individuated qua humanity: that is something shared
by all humans. It is not individuated by belonging to Abraham: ex hypothesi,it
3 So at least he was often understood in the Latin Middle Ages; see CHLMP 393.
4 Though if this interpretation is accepted, then the doctrine that in God essence and
existence are not distinct amounts to saying that the answer to the question ‘What is God?’ is
‘There is one’. Some theologians appear happy to accept this.
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An autograph manuscript of Aquinas, from the Ambrosian library in Milan.
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could exist, and be the same individual, even if Abraham had never been
created but remained a perpetual possibility. It can only be identiWed, as
Avicenna says, by the properties and accidents that accompany it—that is
to say, by everything that was true of the actual Abraham—that he
migrated from Ur of the Chaldees, obeyed a divine command to sacriWce
his son, and so on. Of course, since Abraham’s essence was there before
Abraham existed, it could not be individuated by the actuality of these
things, but only by their possibility.
But, prior to Abraham’s conception, there was no one and nothing to be
the subject of these possibilities. There was only the abstract possibility that
there should be an individual who migrated from Ur, sacriWced his son, and
so on; it was not the possibility of this individual. Similarly, before Noah was
conceived, there was not the possibility that he would build the Ark, but
only the possibility that someone would build an Ark. Avicenna rightly
insisted against Plato that there was no actualization without individu-
ation—there were no actual universals in existence. It was a pity that he
did not accept the converse principle that there can be no individuation
without actualization.
Aquinas on Actuality and Potentiality
The ideas of Avicenna were powerful throughout the high Middle Ages.
Traces of his thought are often to be found in the work of Thomas
Aquinas, whose early metaphysical manifesto On Being and Essence begins
with a quotation from Avicenna to the eVect that being and essence are the
Wrst things grasped by the intellect. As his thought matured, Aquinas
developed his own version of Aristotelian metaphysics, but he never
wholly shook oV Avicenna’s inXuence.
The key concepts in Aquinas’ metaphysics are those of actuality and
potentiality. He derives the notions, obviously, from Aristotle and from
Aristotle’s commentators; but he applies them in new areas and with new
degrees of sophistication. Already in Aristotle the simple pairing of the
concepts had been modiWed by a distinction between Wrst and second
actuality: Aquinas developed this distinction into a stratiWcation of levels
of potentiality and actuality, in particular making a systematic study of the
notion of habitus, or disposition. In Aristotle the two principal instances of
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the potentiality–actuality structure are the relationships of subject to
accident and matter to form. Aquinas accepts and elaborates Avicenna’s
addition of a third instantiation of the dichotomy: essence and being.
Aquinas devoted Wve questions of the Summa Theologiae, Prima Secundae,to
the notion of habitus. The immediate purpose of this treatise (which, though
Aristotelian in spirit, is largely original work) is to introduce the notion of
virtue. But the concept of habitus has much wider application: indeed it is an
essential element in the characterization of peculiarly human behaviour
and experience, even though great philosophers have sometimes seemed
almost unaware of this fact. Aquinas has the merit of having grasped the
importance of the concept and of having been the Wrst great philosopher to
attempt a full-scale analysis of it.
Examples of habitus include—as well as virtues like temperance and
charity—sickness and health, beauty and toughness, knowledge of logic
and science, beliefs of any kind, and the possession of concepts. The variety
of examples shows that the word ‘habit’ will not do as a translation; the
nearest contemporary philosophical term is ‘disposition’. The notion of
disposition is best approached via the notions of capacity and action. Human
beings have many capacities that animals lack: the capacity to learn
languages, for instance, and the capacity for generosity. These capacities
are realized in action when particular human beings speak particular
languages or perform generous actions. But between capacity and action
there is an intermediate state possible. When we say that a man can speak
French, we mean neither that he is actually speaking French, nor that his
speaking French is a mere logical possibility. When we call a man generous,
we mean more than that he has a capacity for generosity in common with
the rest of the human race; but we need not mean that he is currently
doing something generous. States such as knowing French and being
generous are dispositions. A disposition, Aquinas says, is half-way between
a capacity and an action, between pure potentiality and full actuality (ST 1a
2ae 50. 4).
Not every activity, for Aquinas, is an exercise of a disposition. God’s
thought and the motion of planets are activities that spring from no
dispositions. Natural agents need no dispositions in order to perform
their natural activities. By nature Wre heats and water wets: these are the
natural activities of Wre and water and the only activities for which they
have capacities. Where capacity and activity are identical as in God, or
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where capacity can be realized only in a single activity, as with the planets
and natural agents, there is no room for a third term between capacity and
activity.
Dispositions are qualities: they fall into one of the nine Aristotelian
categories of accident. Accidents inhere in substances, and that goes also for
dispositions. All attributes, Aquinas stresses, are in the last analysis attri-
butes of substances, and all a person’s dispositions are dispositions of a
human being. What believes, or is generous, or is healthy is, strictly
speaking, a man and not his mind or his heart or his body (1a 2ae 50. 2).
Still, it is not senseless to ask, say, whether skill in writing history is
principally a gift of memory or of imagination. To ask whether something
is a disposition of mind or of body is to ask whether it belongs to a human
being qua intelligent bein g or qua animal of a particular constitution.
Once again, in attaching dispositions to particular faculties as well as to
the substance in which as accidents they ultimately inhere, Aquinas is
applying a network of stratiWcation to the original Aristotelian dichotomy
of actuality and potentiality. The results are sometimes surprising. No
human activity, he maintains, issues from a purely bodily disposition.
Bodily activi ties are either subject to voluntary control or they are not. If
they are not, then they are natural activities and as such need no dispos-
ition to account for them. If they are, then the dispositions that account
for them must be located primarily in the soul. Thus, for Aquinas, the
ability to run a marathon is a disposition of the soul no less than the ability
to read Hebrew (1ae 2ae 50. 1).
In general, Aquinas’ treatment of the relation between substance and
accident is a natural development of his Aristotelian original. But one
highly innovative application of the concepts is Aquinas’ account of the
Eucharist, the sacrament in which Catholics believed that bread and wine
were changed, by the words of the priest at Mass, into Christ’s body and
blood. The substance of bread, he maintained, gave way to the substance of
Christ’s body—that was transubstantiation—and what remained, visible and
tangible on the altar, were the mere accidents of bread and wine. The
shape, colour, and so on of the bread remain without a substance to inhere
in (ST 3a 75–7).
It is hard to decide whether the concept of accidents inherent in no
substance is a coherent one. On the one hand, the idea of the Cheshire cat’s
grin without the cat seems absurd; on the other hand, the blue of the sky is
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not the blue of anything real and so perhaps is an accident without a
substance. But St Thomas’ account seems to fail in its purpose of explaining
the presence of Christ on the altar: for one of the Aristotelian accidents is
location, and so ‘is on the altar’, like ‘is white and round’, simply records
the presence of an accident inhering in no substance and tells us nothing
about the location of Christ. At all events, this particular application of the
concepts of substance and accident would certainly have taken Aristotle by
surprise.
But if Aristotle wou ld be unlikely to countenance accidental forms
existing apart from a substance, he left his followers in some doubt about
the possibility of substantial forms existing apart from matter. Aquinas, like
Aristotle, frequently objects to Plato’s postulation of separated forms; but,
unlike Bonaventure, he rejects universal hylomorphism and regards angels
as pure forms. Unlike the Ideal Bed or the Idea of Good, angels such as
Michael and Gabriel are living, intelligent beings; but so far as metaphysical
status goes, there seems little diVerence between Plato’s Forms and Aqui-
nas’ angels. Typical of the ambiguity in Aquinas’ position is the following
passage from his treatment of creation:
Creation is one way of coming into being. What coming into being amounts to
depends on what being is. So those things properly come into being and are
created, which properly have being. And those are subsistent objects. . . . That to
which being properly belongs, is that which has being—and that is a subsistent
thing with its own being. Forms, and accidents, and the like, are not called beings
because they themselves are, but because by them something else is what it is.
Thus whiteness is only called a being because by it something is white. That is why
Aristotle says that an accident not so much is but is of. So, accidents and forms and
the like, which do not subsist, are rather coexistent than existent, and likewise
they should be called concreated rather than created. What really gets created are
subsistent entities. (ST 1a. 45. 4c)
The passage as quoted is admirable as a statement of forthright Aristote-
lianism against any Platonic reiWcation of forms, whether substantial or
accidental. But in that very passage, in a sentence that I deliberately omitted,
Aquinas divides the subsistent entities, which alone really have being and
are created, into two classes: hylomorphic material substances on the one
hand, and separated substances on the other. But separated substances—
angelic spirits and the like—are, as understood by Aquinas, forms that are
not forms of anything, and his way of conceiving them seems open to all the
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objections an Aristotelian would make against a Platonist. It seems diYcult
to render Aquinas’ teaching coherent on this topic, other than by saying
that he is an Aristotelian on earth, but a Platonist in heaven.
The most important way in which Aquinas, for better or worse,
ampliWes the Aristotelian system of potentiality and actuality is by applying
it to the pair of concepts essence and existence , which he took over from
Avicenna. For Aquinas, as for Avicenna, there are not just generic essences,
such as humanity, but also the individual humanities of Peter and Paul. There
are also two diVerent kinds of existence, or two di Verent senses of ‘esse’, the
Latin verb ‘to be’ when it is used as equivalent to ‘exist’. There is, Wrst,
generic existence, the existence of a kind of thing: as in ‘Angels exist’ or
‘There are angels’. There is also the individual existence of particular
objects as in ‘The Great Pyramid still exists, but the Pharos of Alexandr ia
does not’. (In Latin the use of ‘est’ and ‘non est’ is quite natural in such
contexts; but in English ‘Rome is, but Troy is not’ has an archaic X avour.)
Generic existence is the kind of existence that philosophers, since Kant,
have insisted ‘is not a predicate’; it is expressed in modern logic by the use
of the particular quantiWer (for some x, x is an angel). Individual existence,
on the other hand, is a perfectly genuine predicate.5
With regard to generic existence, Aquinas’ teaching is quite clear. A
classic text is from De Ente et Essentia:
Whatever [belongs to a thing and] is not part of the concept of an essence or
quiddity is something that arrives from outside and is added to the essence;
because no essence can be conceived without the elements which are parts of
the essence. But every essence or quiddity can be conceived without anything
being understood with respect to its existence; for I can understand what a human
being is, or what a phoenix is, and yet be ignorant whether they have existence in
the nature of things. Hence it is clear that existence is diVerent from essence or
quiddity ...(DEE 4. 94–105)
Whether there are things of a certain kind is quite a diVerent issue from
what things of that kind are: whether there are any angels is not at all the
same question as what ‘angel’ means. If this is what is meant by saying that
essence and existence are really distinct, then the doctrine is undoubtedly
correct.
5 In my book Aquinas on Being (Oxford: Oxford University Press, 2002) I have listed twelve
diVerent senses of ‘esse’ in Aquinas.
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It is not so easy to work out what, for Aquinas, is the relation between
individual essences and individual existence. Is there a real distinction
between Peter’s existence and Peter’s essence—or between either of these
and Peter himself? Surely not: it seems that Peter, Peter’s humanity, and
Peter’s existence all have exactly the same duration; they all begin, roughly
speaking, a few months before Peter’s birth and end with Peter’s deat h.
But perhaps one could argue for a real distinction between essence and
existence in the following way. While it is true that any creature’s existence
persists for exactly the same length of time as its essence, there is this
diVerence, that its existence at one time does not have consequence s for
its existence at a later time in the way that its essence at one time may have
consequences for its existence at a later time. A human being tends to go on
living for a certain time; a radioactive element tends to go out of existence at
a certain rate. These tendencies are part of the relevant essences: it is because
of the kind of thing they are that these creatures tend to continue or to
cease to exist. Essence, therefore, would be distinct from existence, as a
cause—a formal cause, in this case— is distinct from its eVect.
Aquinas’ teaching on the relation of essence and existence is obscure
partly because the word ‘esse’, in addition to meaning ‘existence’ in both of
its senses, has a variety of meanings in which it corresponds to the word
‘being’. Sometimes, for instance, St Thomas tells us that all the things of
diVerent kinds in the universe—mice and men, storms and seasons, virtues
and vices, times and places—have it in common that they are. Being in this
sense is a very thin and universal predicate. (Gilbert Ryle once character-
ized it as ‘like breathing, only quieter’.) At other times the verb ‘to be’ is
used to mark a transition from potentiality to actuality. A caterpillar has
the capacity to become a butterXy, but as long as it remains a caterpillar it
is not a butterXy. Only when the magic day comes can we say: now it is a
butterXy.
These senses of ‘be’ are important in Aquinas’ system only when he uses
them in order to clarify his thesis that in God, unlike creatures, there is no
distinction between being and essence. God is, he claims, pure Being. Not
only the distinction between essence and existence, but also the distinctions
between other forms of potentiality and actuality—substance and accident,
matter and form—hav e no place when we want to give an account of God,
for he is pure actuality. These doctrines will be analysed in the Wnal chapter
of this book, on philosophy of religion.
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The Metaphysics of Duns Scotus
In the system of Duns Scotus, metaphysics occupies a fundamental place. It
is a metaphysics stated in Aristotelian terms, but given a very personal
interpretation. Like Aristotle, Scotus deWnes metaphysics as the science that
studies being qua being; but whereas in Aristotle, to study som ething qua
being was a special way of studying, in Scotus, being qua being is a special
object for study. Being qua being is indeed the broadest possible object of
study, including Wnite and inW nite being, actual and possible being.
In Scotus as in Aquinas it is a principal concern of metaphysics to
establish the existence and attributes of God, so that natural theology is a
branch of the discipline. But for Scotus the scope of natural theology, and
therefore of metaphysics, is both broader and narrower than it is for
Aquinas. It is broader, because Scotus believed that the terms that signify
the fundamental properties of being qua being—such as ‘good’, ‘true’, ‘one’,
and so on—applied not just analogously, but univocally to God as well as
to creatures. But it is narrower, because many truths about God that
Aquinas had treated as accessible to natural reason are regarded by Scotus
as graspable only by faith. Aquinas had thought that reason could prove
that God was omnipotent, immense, omnipresent, and so on. Scotus, on
the contrary, thought that reason was impotent to prove that God was
omnipotent. A Christian, he argued, knows that among the powers of an
omnipotent God is the power to beget a Son; but this is not a power that
pure reason can show God to possess. Thus many topics that, for Aquinas,
were within the scope of the metaphysician are by Scotus assigned to the
dogmatic theologian.
It was common place among scholastics to say that ‘being’ was a tran-
scendental term that applied across the Aristotelian categories, and to say
further that every being of every kind had properties like goodness and
unity. Scotus’ innovation in this respect was the claim that transcendental
predicates such as ‘being’ and ‘good’ were univocal, not analogical.6 But
there is a diVerent kind of transcendental to which Scotus attached great
importance: the transcendental disjunction. He drew up a list of pairs of
terms of which one or other must apply to whatever there is: every being
must be either actual or potential, W nite or inWnite, necessary or contingent.
6 See Ch. 3 above.
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