St. Thomas and Avicenna on the Nature

of the One

In several of his major works St. Thomas attributed to Avi cenna certain doctrines on the nature of the one which, if verified, would limit the Arabian philosopher to a univocal view of reality in terms of quantity, and ultimately in terms of matter. This

judgment of Thomas on Avicenna's notion of unity has determined the attitude of most Scholastics toward him on the same point down

to the present time. Moreover, as an estimate that involves im

portant consequences in any total view of Avicenna's thought, it is in contrast with the indebtedness that Aquinas more than once

acknowledged to him in establishing fundamental principles in his own metaphysics.

St. Thomas based his evaluation on the only one of Avicen na's writings available to him. This was the Shifà, his most ex tensive but also his earliest work, of which the section on meta

physics had been put into Latin, rather imperfectly, by Dominicus

Gundissalinus in the previous century. It would, then, seem op portune to ask to what extent the doctrines ascribed to the Arabian

are actually his, especially by reference to the originai text of the

Shifà and to the works bv the same author that followed it.

The errors which Thomas attributed to Avicenna in regard to

the nature of unity may be formulated under four headings. First, Avicenna is said to have questioned the definition of one as being considered as undivided. « The true definition of one is being which is not divided, although Avicenna endeavors to find fault

with it »1. Second, in both his earlier and later works St. Thomas

expresses the opinion that Avicenna confused transcendental unity

with predicamental.

For Avicenna (III tract. Metaph. c. vi) says that one which is

converted with being is the same as one which is the principle of

number2.

11 In I Seni., d. 24, q. 1, a. 3, ad 3. 2 In I Seni., d. 24, q. 1, a. 3, c.

666 Τ. o'sHAUGHNF.SSY, S. I.

Avicenna... said... that one and being signify, not the substance

of a thing, but something added.

For he thought that the one which is convertible with being is the

same as the one which is the principle of number3.

From this second error of Avicenna, says Thomas, there

follows a third. If transcendental unity is the same as predica mental unity, which follows upon the real accident of quantity, distinct from substance, then transcendental unity must also add a real accident to being4. In fact, says St. Thomas, «Avicenna... believed that the one which is convertible with being adds some

thing to the substance of being, as white does to man »5. But he

evidently erred, he continues, because the superadded reality itself would be one by another reality, and this third by another, and so to

infinitye. The Arabian's mistake arises from the twofold meaning one has. As a measure of quantity, one is limited to a genus and

implies a real accident distinct from the substance modified, but, as convertible with being, one is not thus limited, as it is common to ali beings 7.

A fourth error, which is also a consequence of Avicenna's

confusion of transcendental with predicamental unity, says St.

Thomas, is his making every multitude a result of quantitative

division 8. But the truth is that, besides this material division of the continuum, there is division that depends on the opposition be

tween forms that present several degrees of perfection. The mul

titude resulting from this formai division is transcendental and is rriet with in the realm of immaterial beings 9. Although in the

proper sense number belongs only to the order of material plural

ity, it can be predicated in a transcendental sense by analogy, se

cundum prius et posterius10, of beings without matter and quan

3 In IV Metaph., lect. 2, nn. 556-57. 4 « Si ergo unum quod convertitur cum ente sit idem quod unum quod

est principium numeri, oportet quod etiam unum quod convertitur cum ente

aliquid positive superaddat enti : et hoc concedit Avicenna : unde vult, quod unum quod convertitur cum ente, addat supra ens aliquid quod ad genus men surae pertineat » (Quodl. X, q. 1, a. 1).

3 5". Τ., I, q. 11, a. 1, ad 1. 3 Ibid. 7 In X Metaph., 1. 3, 1980-81. Cf. In IV Metaph., 1. 2, 556, and Quod

libet. XII, q. 5, a. 5. 8 De Potenzias, q. 9, a. 7. 9 In III Phys., 1. 12; 5". Τ., I, q. 30, a. 3. 10 In V Metaph., 1. 8, 875.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 667

tity. « It is not true that ali number is caused by matter, for in

that case Aristotle's seeking the number of separateci substances

would have been useless » u. St. Thomas expresses these four points of disagreement in

clearer1 terms than any that are likely to be found on the same

subject in Avicenna. Nevertheless, by a closer examination of the

Shifà in conjunction with works not available to Aquinas, it may be possible to determine to what extent these statements on the

nature of unity can rightly be attributed to the Arabian. In regard to the definition of the one, Avicenna is explicit in

asserting that it is nothing but being viewed from the aspect of « what has no actual division »12. « One is said of whatever is

indivisible — indivisible in that respect in which it is said to be one » 13. The same conception of the one is implied in the De Ani

ma where it is contrasted with a multitude which arises from form

or matter or from causes that effect division 14.

In the face of such unequivocal statements by Avicenna about

the nature of one, it may be enlightening to look more closely at

the context of St. Thomas's remark that he questioned the tra

ditional definition. In I Sent., d. 24, q. 1, a. 3, 3, Thomas proposes the following difficulty : Since multitude implies a removal of uni

ty, unity necessarily occurs in the definition of multitude. But

this leads to a vicious circle (because the previous objection stated

that multitude must occur in the definition of unity). Thomas's

answer is : The true definition of one is being which is not divided,

although Avicenna in the Metaphysics 15, tract. Ili, c. vi, tries to find

fault with it by this objection. For there are two kinds of division :

first, quantitative (and quantitative division does not occur in the

definition of transcendental one) ; second, division according to

form or essence, and this division originates in affirmation and

negation, which two must precede in the mind the notion of one.

11 Leo W. Keeler, editor, De Unitate intell. centra Averroistas (Romae, Pont. Univ. Greg., 1936) c. V, n. 102, p. 65.

12 « Dicam igitur quod unum dicitur ambigue de intentionibus quae sic

conveniunt quod in eis non est divisio in effectu, in quantum unumquod

que eorum est id quod est » (Metaphysica Avicennae sive eius prima philoso

phia, Venetiis, Bernardinus Venetus, 1495, no pagination, tract. Ili, cap. 2.

Kitàb al-Shifà' (Tehran, 1886) voi. II, p. 425. 13 Nematallah Carame, trans., Avicennae Metaphysices Compendium,

Roma, Pont. Institutum Orientalium Studiorum, 1926, p. 64; Ibn Sina, Al

Najàt, Cairo, Al-Sa'àdah, 1331 A. H., p. 364. 14 George P. Klubertanz, editor, Avicenna — De Anima, liber excerptus

ex editione Venetiis 1508, St. Louis, St. Louis University, 1949°, pp. 119-120.

Kitàb aì-Shifà', « Al-Tabi'àt », VI, 3 (Tehran ed., voi. I, p. 353).

668 Τ. o'sHAUCHNKSSV. S. I.

It should be noted that St. Thomas does not say that Avicenna

denies that one is being which is not divided. Rather he says that Avicenna nitatur eatn improbare, that is, « tries to find fault with »

that definition. This Thomas himself also does by presenting an

objection that might be made against it. Avicenna offers the same

objection, not in the sixth, but in the third chapter of tract three, and not as his own opinion, but rather as an illustration of the

difficulty of defìning one and as an introduction to the explanation of one which he here proposes to give 16.

A brief summary of this chapter in Gundissalinus's Latin version used by St. Thomas will help to make this clear : (1) It is difficult to define one, for, if we say it is that which is not divided

(that is, multiplied), we use multitude to explain one. But one in turn necessarily enters into the definition of multitude. Although an adequate explanation is for this reason difficult, we can never

theless say that multitude and unity are among those things which we first grasp : multitude by the imagination and unity by the intellect. Unity, then, is understood immediately and multitude be means of unity. Since unity is first understood in itself, we do not really define unity by saying that it is that in which there is no multitude. Multitude, moreover, is not rightly defined by num

ber, because multitude is the genus of number. Rather, multitude

is made up of units of the same species; units not of the same

species can be said to be many, but not a multitude. (2) Both ac cidente and substances can have one as a predicate. When pre

dicated of substances, one is not part of the essence as genus or

difference but is predicated as an inseparable logicai accident (co mitans). Although unity is not a constitutive part of the essence of a substance, yet it is impossible for it to be separated from sub stance. The one, then, in both substances and accidents, is being (esse) which is not divided. Accidents have unity because of the

unity of the substance17.

St. Thomas himself gives evidence of recognizing Avicenna's

15 References to Avicenna's Metaphysics are to the Latin translation of

Gundissalinus, Metaphysica Avicennae sive eius prima philosophia Vene tiis Bernardinus Venetus, 149S.

:ie Similarly it might be inferred from the way in which Avicenna is cited in In I Sent. d. 24, q. 1, a. 3, 1 that he holds one to be the privation of a privation. In the chaipter there referred to (Metaph. tr. Ili, cap. 6) Avicenna says that certain philosophers tried to show a privative opposition between one and many by this kind of reasoning — which he then proceeds to prove fallacious.

17 Avicenna, Metaph., tr. Ili, cap. 3.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 669

real position on the nature of one, when in the first article of the same Distinction (the twenty-fourth) he cites the Arabian as up holding the distinction between numerical and transcendental unity. « According to Avicenna the unity and number which the arith metician deals with are not the unity and multitude found in ali

things »18.

Is it exact, then, to say, as Thomas does elsewhere, that Avicen

na confused numerical or predicamental unity with transcendental? At first sight it might seem so because of the peculiar way in which the Arabian philosopher sometimes uses the term number. For

example, finite immaterial substances in as much as they laek

matter, the principle that enables the essence to be shared by many,

cannot be multiplied within the species, and so « such a species is one in number » 1B. But here number is evidently to be understood in a transcendental sense — a sense occasionally employed by St. Thomas himself 20. Again, according to Avicenna, that which is one in number may be actually many in another way, by compo

sition or aggregation. If it is many, not actually, but only po tentially, then it will be a continuum, predicamentally one. If it is not even potentially many, then it is « one in number in an absolute sense »21. Avicenna distinguishes the two kinds of unity more

clearly in one of his last works, 'Uyùn al-Hikmah 22. There we are told that being, to be one, need not pertain to the realm of

mathematics or sensible nature. Unity is numbered among the

essential accidents (al-a!ràd al-dhàtiyah) present to existent being which are adventitious to it in so far as it is existent being. Other

wise the one being would necessarily belong to the realm of ma

thematics or sensible nature 23. The same opposition between pre

Τη Τ <\pnt Η 74 η 1 a 1 ad ? 19

Shifà', V, 2 (Teh'ran ed., voi.' II, p.'490) ; Metaph., tr. V, cap. 2. 2° Τ., I, q. 50], a. 3, ad 1. 21 Carame, op. riè,, p. 65; Najàt, p. 365. 22 Among the more important writings of Avicenna which contain trea

tises on logie and metaphysics are, in the order of their appearance, the

Shifà («Healing»), the Najàt (« Deliverance »), and Al-Ishàràt wfal-Tan

bìhàt (« The Directives and Remarks »). His Dànish-Nàmeh (« Book of

Knowledge»), a work of smaller scope, was composed while the Shifà was

stili unfinished. Mantiq al-Mashriqiyin (« The Logic of the Orientale ») seems to be a fragment of a larger composition now lost. Among his many shorter

works 'Uyùn al-Hikmah (« The Sources of Wisdom ») merits special mention

as a brief summary of his philosophical thought written in the last years of

his life. Ali these works are in Arabie except Dànish-Nàmeh which is in

Persian. 23 Abdurrahmàn Badawi, editor, 'Uyùn al-Hikmah, Cairo, Institut fran

cali d'archéologie orientale du Caire, 1954, p. 47.

670 Τ. o'SHAUGHNESSY, S. I.

dicamental and transcendental unity is implied in the Mantiq al

Mashriqiyìn where the subject matter of logie is said to be those

things sometimes associated with matter, sometimes not, « such as

unity and multiplicity »24. The Dànish-Nàmeh speaks more ex

plicitly of the division of the real ση e (1) into the one that is multiple in no respect, like God, and (2) the one potentially or actually many,

actually if it is one composite or aggregate, potentially if it is a continuum and so subject to quantitative division 25. The objects of primary concepts, however, are transcendental, that is, « common

to ali things, as being, thing, and one are »26.

Thirdly, can it rightly be said that Avicenna looked on trans cendental unity as resulting from the addition of a predicamental accident to being? St. Thomas regards this added accident of

Avicenna as quantity27 and, if it is held to be such, the question is really answered in the point immediately preceding, as Avicenna

considered transcendental unity to be independent of matter and therefore also independent of quantity. Moreover, he speaks of

transcendental unity in a way that excludes its connection with

any real accident. The Necessary Being is one, he asserts, be

cause He is not divided quantitatively nor by constitutive parts nor by the (logicai) parts used in defining. Besides the unity that

every being has, that is, unity proper to it by its essence, He is also one because His manner of existing

— necessity

— is proper

to Him alone2S. « When He [the necessarily existent] is called

one, the meaning is a being that has no equal or a being that has

no part » 29. Since modification by a predicamental accident implies composition, a being without parts of any kind is one without the addition of a predicamental accident. Its unity therefore is trans cendental and coextensive with being itself ; « ... ali that can be

trulv said to be being can also be truly said to be one »30.

124 Mantiq al-Mashriqiyin, Cairo, Al-Muayad Press, 1910, ρ. 7.

25 Mohammed Achena et Henri Masse, trad., Avicenni — Le lime de science, Paris, Les Belles Lettres, 19SS, I, p. 121.

26 Shifà' I, S (Tehran ed., voi. II, p. 291). « Quae autem promptiora sunt ad imaginandum per seipsa sunt ea quae commissa [i.e., communia, for al

'ammali] sunt omnibus rebus sicut res et ens et unum et caetera» (Metaph tr. I, libri 2', c. 1). «Imaginandum» is an inexact translation of mutasawwa

rah, « formed » or « conceived » as an obj ect of thought. 27 « Avicenna... vult, quod unum quod convertitur cum ente addat supra

ens aliquid quod aid genus mensuraje pertineat » (Quodlib. X, q. 1, a. 1). 28

Carame, qρ. cit., p. 80; Najàt) p. 375. 129 ' Uyùn al-Hikmah, p. 59. The same description is found in Dànish

Nàmeh, Achena et Masse, op. cit., I, 149. 30 Carame, op. cit., p. 2; Najót, p. 323.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 671

Finally, does Avicenna make every kind of multitude a result

of quantitative division? Evidently not, as is clear from his teach

ing already referred to31, that is, that multiplicity is possible even

independently of matter. Consequently, beings that have no prin ciple of multiplication in the order of essence form a transcendentai

multitude composed of many distinct and opposed species.

A nature which needs no matter to remain in existence or to begin to exist cannot be multiplied but its species subsists as one in number 32.

The question that now occurs is how St. Thomas carne to attri bute to the Arabian doctrines that are not verifìed in the latter's works. Since his fundamental objection is to Avicenna's making both transcendentai and predicamental unity result from a real accident added to substance, it is clear that in his criticism Thomas followed Averroes 33. Although the latter, with his great weight of authority, might have been expected to interpret correctly a

philosopher who also wrote in Arabie, yet it was precisely in regard to the present subject — the nature of unity — that he accused Avicenna of serious error:

Avicenna confused the nature of the one which is the principle of number with the absolute one common to ali the predicaments, and, since the one which is the principle of number is an accident, he

thought that the absolute and transcendentai one is also an accident34.

If Averroes's misunderstanding was sincere, it may have

arisen from the fact that Avicenna looks on both kinds of unity as logicai accidents in the order of predication 35. In this order

131 See note 24 supra. 32 Shifà', V, 2 (Tehran ed., voi. II, ρ. 490); Metaph. tr. V, cap. 2. 33 St. Thomas's indebtedness to Averroes on this point has often been

noted; for example, by S. Munk, Mélanges de philosophie juive et arabe, Paris, Vrin, 19SS, p. 359; Aimé Forest, La structure métaphysique du con erei selon Saint Thomas d'Aquin, second edition, Paris, Vrin, 1956, p. 41 ; and Etienne Gilson, Le Thomisme, fifth edition, Paris, Vrin, 1947, p. 56.

34 Carlos Quiros Rodrìguez, editor, Averroes Compendio de metafisica, Texto arabo con traducción y notas, Madrid, Imprenta de Estanislao Maestre,

1919, p. 104 (III, n. 41). Averroes is even more explicit in his Commen

tary on Aristotle's Metaphysics, lib. X, summae primae cap. 4 : « Et Avi

cenna ... non opinatur quod res est ens per se, sed per dispositionem additam

ei : ut dicimus aliquid esse album. Unum igitur et ens apud ipsum significant accidens in re» (Aristotelis Stagiritae Metaphysicorum Libri XIIII cimi

Averrois Cordubensis in Eosdem Commentariis, Venetiis, apud Iuntas, 1553, voi. 8, p. 121 r, col. 1, lin. 1-5).

35 See A. M. Goichon, La distinction de fessence et de l'existence

d'après Ibn Sina, Paris, Desclée De Brouwer, 1937, pp. 9-12.

672 X. o'SHAUGHNESSY, S. I.

a real accident is regarded as not constitutive of the essence of

the substance it modifies and so is, in Avicenna's understanding of

the term, a logicai accident. So far, however, was he from confus

ing the two kinds of accident that he explicitly warns against such

a mistake in one of his major works:

The property and the common accident are among the accidental

predicates ... An example of the common accident is 'white' with a

man of the white race... Some modem logicians [the Arabs as con

trasted with the Greeks, the ancients] think that this accident is the

one mentioned as opposed to substance (yuqàl ma'a Ί-jawhar), but it

is by no means so... These five expressions, genus, species, difference,

property, and common accident... are attributed to particular things which are their [logicai] inferiors 3e.

From Avicenna's viewpoint this connection between unity and

logicai accident seems to have occurred naturally. One evidence

of this is the dose association of the two in the Najàt where his treatment of being and the one includes a chapter on the

various kinds of predicables 37. In the Shifà he speaks even more

plainly of the accidental character of one :

When unity is predicated of substances it is not predicated of them as a difference nor as a genus ; for it does not enter into what deter mines the quiddity of any substance; but it is something that accom

panies substance, as is clear. So it is not predicated of them as a genus nor as a difference but as an accident3S.

For Avicenna a logicai accident properly so called is « an accidental universal », namely, « that by which the essence is de scribed after [being constituted] »39. An accidental universal is a

property if it is coextensive with one species and hence predicable only of it, but it is a common accident, if predicable of many species or of the individuals of many species40. St. Thomas recognizes a like division when he says that certain accidents belong to the

3β Α. Μ. Goichon, trad., Ibn Sina, Livre des directives et remarques, Paris, Vrin, 1951, pp. 100-102; Ibn Sina - Le livre des théorèmes et des avertissements publié d'après les mss. de Berlin, de Leyde et d'Oxford, 1*

partie - texte arabe, J. Forget, editor, Leyde, E. J. Brill, 1892, pp. 15-16. 37 Carame, op. cit., pp. 2-3 ; Najàt, p. 323. 38 Shifà' III, 3 (Tehran ed., voi. II, p. 431) ; Metaph., tr. Ili, c. 3. 39 'Uyun al-Hikmah, Badawi ed., p. 2. 40 Ibid. Cf. Goichon, La distinction, p. 120, and A. M. Goichon, Lexi

que de la langue philosophique d'Ibn Sina, Paris, Desclée De Brouwer, 1938, pp. 217-18.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 673

species and are called properties, like risible in man, while others

belong to individuals of the species 41. It is in this sense (with the accommodations required by a

transcendental subject) that Avicenna speaks of unity in general as one « of the accidents that inseparably follow (al-làzimah) upon

things », and as « an attribute (sifah) inseparably following upon the essence », and in the same context warns that « the one is not

a constituent part (muqawwin) of the quiddity of anything »42.

Unity in the narrower sense, that is, predicamental unity which results from real quantity, is also in the order of reflex universals a logicai accident :

Clearly the nature of unity is an accidental nature and so also is

the nature of number which follows upon unity and is made up of

it43.

We say that number is an accident because number comes from

unity, and the unity found in things is an accident, for example, one

man and one water. Humanity and aqueity are things other than

unity. Unity is an attribute of both, but an attribute extrinsic to

their essence and quiddity. For this reason one water becomes two

and two become one, as has already been shown [where it was de

monstrated that a body is not made up of actual parts]. But one

man cannot become two because [his unity] is an accident inseparable from him44.

According to Avicenna, therefore, the adequate concepì of any finite45 essence does not include unity as a constitutive note.

« From the fact that you understand the quiddity of anything, you do not on that account understand one, nor would [your under

standing of the quiddity of a thing] justify you in saying that the

thing is one » 46. Predicamental unity ontologically coexists with the material substance of whose number it is the principle, but

logically this same unity is related to its subject as an accident47.

Consequently any essence absolutely considered, that is, apart

from its existence in the individuai or in the mind, is neither one

nor many.

41 Quaest, disp. de anima, a. 12, ad 7.

42 Carame, op. cit., p. 28; Najàt, pp. 340-41. 43

Carame, op. cit,, p. 29; Najàt, p. 341. 44 Achena et Massé, op. cit., I, pp. 111-112; cf. also p. 104. 45 The unity of the Necessary Being is treated separately - in Carame,

op. cit., p. 80; Najàt, p. 375. 46 Carame, op. cit., p. 28 and note 3; Najàt, p. 340. 47 See Beatrice H. Zedler, Saint Thomas and Avicenna in the 'De

Potentia Dei', Traditio, 6 (1948) 153.

5 — « Gregorianum » XLI (i960) - voi. XLI.

674 Τ. o'SHAUGHNESSY, S. I.

Equinity in itself is nothing but equinity, for in itself it is nei

ther one nor many, nor existing in concrete individuals nor in the

mind 4S.

When the question is proposed : ' The individuai substance of man

in so far as he is man, as something one — is it one or many?' no reply is necessary, for it, in so far as it is the individuai substance

of man, is something other than both [one and many], for in the defi

nition of this thing nothing is found but humanity only49.

A nature is specifìcally one from its forra50, but individuai

unity — based on unicity of form or on matter, depending on the nature of the being — is related to the essence as a logicai accident. « For if multiplication were owed to human nature of itself, then man would not be predicated of anything numerically one »51.

Nevertheless, though not part of any finite essence, individuai

unity is inseparable from the existing individuai. In a similar way Avicenna argues that multiplicity cannot be

part of human nature, because then « every individuai... would be many from the fact that he is a man. And so multiplicity comes

accidentally to him by a cause » 52. St. Thomas uses the principle implied in this reasoning to prove that existence is predicated of finite beings as a logicai accident. The argument proceeds from the premise that whatever is had from a cause is something other than the essence.

Ali that anything has ... from another is over and above its es

sence, and so Avicenna proves that the existence of each thing, except the first being, is over and above its essence, because ali [creatures] have existence from another 53.

Finite unity too, depends on a cause and is therefore, as a logicai

accident, extrinsic to the essence. « For », says St. Thomas, « exist

ence, unity, and multitude in [finite] things proceed from the same

principle »54. Even for matter, Avicenna adds, which is the po

48 Shifà' V, 1 (Tehran ed., voi. II, p. 483). 49 Ibid., p. 484. 50 « Forma etenim humana... est natura, in qua conveniunt omnia sin

gularia speciei aequaliter; cuius est una definitio » (Avic. De Anima, II, 2, fol. 6v. bA, Klubertanz ed., p. 28); cf. ibid., fol. 24 r a, p. 119. Cf. Aristo

tle, Metaph. V, 6, 1016 b 33. 51 Ibid., II, 2. fol. 6vb, p. 28; Shifà', «Al-Tabi'àt» VI, ii, 2 (Tehran

ed,, voi. I, p. 296). , 53 'Uyùn al-Hikmah, Badawi ed., p. 57. 53 De Ventate, q. 8, a. 8. 54

Compend. Theol., I, cap. 102.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 675

tential constituent of a material essence, unity and multiplicity are

only logicai accidents 5S. This extrinsic relation of unity to essence holds not only for

substances but also for any predicamental accidents which may modify them.

If the nature of unity were the nature of substance, only sub

stances would be called one. If its nature is that of an accident, sub

stances may be described as one, because accidents are predicated of

substances, but not vice versa... Therefore... unity... is predicable of

accidents ®®.

But, though predicable of accidents, unity is never part of their

essence, but again is always a logicai accident. Like existence,

unity is not a predicable belonging to the essence of anything coming under the ten supreme genera. Both are adventitious to

the essence.

Existence is neither genus nor property nor anything else of

these ten categories. The sanie is true of the accident of unity which,

though applied to ali ten, is neither anything essential nor genus nor

property 57.

The one may coincide with existing being in that the one, like

existing being, is said of each predicament. Their comprehension dif

fers, as is clear, but they are alike in that neither indicates the sub

stance of anything 5S.

Unity, moreover, is applicable not merely of the predicaments, but it is predicable of being itself, for, according to Avicenna,

« first philosophy... seeks... the accidents essential to being in so far as it is being — like unity, multiplicity, and causality »59. It

is in this sense too, that he speaks in the beginning of the Meta

physics of the one and the many as accidental properties :

55 Cakame, ο ρ. cit., ρ. 29; Najàt, ρ. 341. 56 Ibid. 57 Achena et Masse, ap. cit., I, p. 116. 58 Shifà' III, 2 (Tehran ed., voi. II, p. 429). 59 'Uyùn al-Hibnah, Badawi ed., p. 47. The editor notes that the word

« essential » is missing in two of the three complete manuscripts on which

this edition of the 'Uyùn al-Hikmah is based. The reading with «essen

tial », however, seems preferable, as indicating an attribute outside the es

sence but inseparably following upon it. Regarding the non-essential char

acter of causality or relation to cause in a finite being, St. Thomas has a

similar doctrine : «... licet habitudo ad causam non intret definitionem entis

quod est causatum, tamen sequitur ad ea quae sunt de eius ratione: quia ex

hoc quod aliquid per participationem est ens, sequitur quod sit causatum

ab alio. Unde huiusmodi ens non potest esse, quin sit causatum ; sicut nec

homo, quin sit risibile» (5*. Τ., I, q. 44, a. 1, ad 1).

676 Τ. O'SHAUGHNESSY, S. I.

The subject of this science is being as being. Its objects of in

vestigation are those which follow upon being as such without any condition. Some of these are quasi species, like substance, quantity, and quality... and some... are quasi accidental properties, like one

and many...60.

If unity is regarded as an attribute inseparably following upon an

essence, more explicit references to it in other places are better

understood.

Unity is an attribute (sifah) which is joined to equinity, and

with this attribute this [equinity] is one61.

Unity, then, is neither the essence nor part of the essence of any

thing... Rather it is an attribute inseparably following on the essence

of a thing (sifatum làzimatum lidhàtih) — the difference between some

thing inseparably following and something essential (bayn al-làzim

wa Ί-dhàtì) you already know from logie62.

The modem Latin version of the Najàt translates the Arabie term for attribute (sifah) as qualitas, a rendering which might make it seem that Avicenna regarded unity as a predicamental quality. Reference to the Arabie text, however, clearly excludes such an interpretation, since predicamental quality is kayf, while

sifah (said of unity) is an attribute or property, the πάθος of Aristotle and the passio of St. Thomas expressing a property of

being63. It was in this last sense that St. Thomas understood Avi

cenna to take unity, that is, as something inseparably following upon an essence, like risible in relation to humanity.

But [Avicenna] said that one is convertible with being, because

it signifies, not the essence itself of any thing or being, but an acci

dent which is in every being, like risible which is convertible with

man ®4.

The reason for some of the obscurity that surrounds unity

and the other transcendental properties of being is that, when used

to designate them, « property » is taken in a broad sense. Strictly understood, property is something .not expressed by the definition' of a species, but being is not a species and its notion implicitly

60 Shifà' i, 2 (Tehran ed., voi. II, p. 281). " Ibid., V, 1 (p. 483). 62 Carame, op. cit., p. 28; Najàt, p. 340. 63 Carame, ibid. ; Aristotle, Metaph., IV, ii, 17, 1004b 5-6; St. Tho

mas, In Metaph. IV, 1. 4, 571. Cf. a. m. Goichon, Vocabulaires comparés d'Aristote et d-'Ibn Sina, Paris, Desclée De Brouwer, 1939, p. 39.

64 In Metaph. IV, 1. 2, 557.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 677

includes even its own attributes. When being and these attributes, moreover, are said to be convertible, it is understood that the con version is merely material, never formai, since they differ in their determined comprehension — a point that was not missed by Avi cenna. « The one, like actual being, is said of each predicament. Their comprehension differs, as is clear, but they are alike in not

indicating the essence » 65.

Consequently Avicenna, when speaking of unity, uses sifah, attribute, rather than khàssah, property in the strici sense, which latter he defines as « a non-essential universal, predicable of one

species »β6. As with the early Scholastics, so with Avicenna sifah or passio connotes a subject (1) prior to the attribute and (2) upon which the attribute follows inseparably. « The quiddity », he says, « is an essence (shay'), a man or a horse or an intellect or a soul.

Afterwards it is qualified as being one... »67.

* * *

St. Thomas, then, while using much of what Avicenna had to offer in constructing his own metaphysics, followed Averroes's

rejection of his doctrine on the one. Not only does he repeat in almost the same words68 Averroes's accusation that « Avicenna

sinned much in saying that one and being signify dispositions (sifàt) added to the essence of a thing »ββ, but his argument in

QuodUhet. X and the Sutnma 70 that transcendental one conceived

as a predicamental accident would lead to an infinite series closely approximates the following attack of Averroes on the same point :

Avicenna thinks that being and one indicate something added to

the essence... We have already mentioned elsewhere the impossibil ities that follow on this position. First, if there is question of this

disposition or that accident by which the one becomes one ... has it

become one by something superadded or by its essence? If he says, ' By

65 Shifà', III, 2 (Tehran ed., voi. II, p. 429). See Goichon, Lexique,

p. 430. 66 'Uyùn al-Hikmah, Badawi ed., p. 2. 67 Carame, op. cit., p. 28; Najàt, p. 340. 68 For example, In IV Metaph., lect. 2, n. SS6, supra, note 3. 68 Averroes, In IV Metaph., c. 3, Averroès tafsir ma ba' d at-tabi' at,

Texte arabe inédit établi par Maurice Bouyges, S. J., Beyrouth, Imprime rle Catholiqua, 1938, voi. I, p. 313. The parallel in the medieval Latin trans

lation can be found in Aristoteli Opera, Venetiis, apud Iuntas, 1553, voi. 8, in lib. IV, cap. 2, p. 32 r, col. 1, lin. 56 ff.

70 In Quodl. X., q. 1, a. 1 and in 5". Τ., I, q. 11, a. 1.

678 Τ. O'SHAUGHNESSY, S. I.

something superadded', the consequence is an infinite process, and if

he says, ' By its essence it is conceded that there is found something

which is one by its essence. The man [Avicenna] erred... in believing that the one which is the principle of quantity is the one convertible

with being. Consequently he thought that, because this one is num

bered among the [predicamental] accidents, one which indicates ali

the predicaments is also an accident n.

It may have been that St. Thomas in attributing such teach

ings to Avicenna was using his name as a convenient label to

designate a class of doctrines that made the one univocal. In an earlier work, as has already been noted, Thomas admitted that « according to Avicenna the unity... which the arithmetician con siders is not that unity... found in ali beings »72. This might favor the view that he was opposing a tendency rather than an

individuai. Stili it is trae that his practice in earlier works of

citing Avicenna with approvai is gradually relinquished for a less benevolent interpretation in his later years. This change of at titude on Thomas's part seems to have been prompted by the wider reaction in the Church against the heterodox Aristotelianism in

spired by Arabian philosophy which occurred in the last decade of his life 73.

It is likely too that certain errors in Gundissalinus's Latin translation of the Shifà, from which Thomas drew his informa tion about Avicenna's doctrines, confirmed his opinion of the Arabian's teaching on the nature of the one. Some of these errors

rose from defects in the Arabie text, some from an insufficient knowledge of the special terminology employed by Avicenna, and some from the use of the Romance vernacular as a medium be

tween the Arabie and the final Latin version74. Moreover, as

Gundissalinus was a Platonist75, his translation would also have reflected the Platonic confusion between ontological and predica

71 Averroès tafsir ma ba'd at-tabi'at, lib. X, c. 8, b, in Bouyges's ed., Ili, pp. 1279-80. For the reference to the Latin text see footnote 34 supra. Forest, op. cit., p. 41, has already noted this borrowing by St. Thomas.

72 In I Sent., d. 24, q. 1, a. 1, ad 2. 73 See The Modem Schoolman, 36 (1958-59) 259-60. 74 Μ. T. d'Alverney, Notes sur les traductions médiévales des oeuvres

philosophiques d'Avicenne, Archives d'histoire doctrinale et littéraire du moyen àge, 19 (1952-53) 339 and 344. Several of these errors are pointed out by M. Alonso, Traducciones del arcediano O\omxngo Gundisalvo, Al-Andalus, 12 (1949) 335-36.

75 Marie-Thérèse d'Alverny, Les traductions d'Avicenne (Moyen Age et Renaissance), in Avicenna nella storia della cultura medioevale, Quaderno No. 40, Roma, Accademia Nazionale dei Lincei, 1957, p. 75.

ST. THOMAS AND AVICENNA ON THE NATURE OF THE ONE 679

mental unity that carne from making quantity a transcendental in

stead of a supreme genus or predicament76. It is noteworthy

that the very mixing of the two kinds of unity that St. Thomas

finds in Avicenna appears in a traci, De imitate et uno, composed

by Gundissalinus himself and manifesting strongly Neo-Platonic tendencies. It is introduced by a comparison illustrating the

author's notion of unity which was later taken as the teaching of

Avicenna himself on the same subject.

It is by unity that each thing is said to be one, for, whether it is

simple or composite, spiritual or corporeal, a thing is one by unity

and cannot be one except by unity, just as it cannot be white except

by whiteness nor quantitative except by quantity 77.

Here transcendental unity, convertible with being, is made to ap

pear as a reality added to being and comparable to quality or

quantity. It would not be surprising, then, if in a translation

made by the author of this opinion a certain bias should appear that might occasion the interpretation of the Arabian philosopher that St. Thomas actually adopted.

Even the most favorable construction put on Avicenna, how

ever, cannot obscure the fact that in his metaphysical system the

real order tends often to appear as a projection of the logicai. His thought never developed the clarity in distinguishing the two

which characterizes the writings of Aquinas. Yet credit is owed

him for his real contributions to metaphysics which were not

always discernible in an age when his works were only partially known and imperfectly transmitted.

Thomas O'Shaughnessy, S. I.

76 A. D. Sertillanges, La philosophie de S. Thomas d'Aquin, nouvelle

édition, Paris, Aubier, Éditions Montaigne, 1940, pp. 28-29. 77 Paul Correns, editor, Dominicus Gundisalvi de Unitate (Beitrage

zur Geschichte der Philosophie des Mittelalters, Texte und Untersuchungen, Bd. 1, Heft 1) Miinster, Aschendorff, 1891, p. 3. Cf. Forest, op. cit., p. 42.