I. THE PROBLEM IN CATEGORIES

One of the main problems addressed by Aristotle in his Metaphysic¹ is the ontological structure of reality. Although his pre-Socratic predecessors had put forward some theories in this regard, as had his teacher Plato, for the Stagirite the problem was far from being solved and, from his perspective, required further elaboration. A key distinction that Aristotle introduced in the philosophical understanding of the world is the idea that there are certain things exist on their own, and there are those that depend on others to exist. In other words, there are substantial items that exist on their own, and properties or qualities that require those substantial items for their existence. An apple exists by itself, but its red color and sweetness depend on it to exist. There is no sweetness and redness beyond sweet things and red things. This, which seems more or less obvious to us today, would have been understood differently by some pre-Socratic and Hellenistic philosophers (^{Frede, 1987}, pp. 72-73).

Aristotle is particularly interested in explaining how, when it comes to properties, their being depends "on particular objects as their ultimate subject" (^{Frede, 1987}, p. 73). These objects are called ousiai. The first treatment of ousia, or substance,² appears in Cat. It is there that the philosopher deals with this concept and points out:

A substance-that which is called a substance most strictly, primarily, and most of all-is that which is neither said of a subject nor in a subject, e.g. the individual man or the individual horse. The species in which the things primarily called substances are, are called secondary substances, as also are the genera of these species. For example, the individual man belongs in a species, man, and animal is a genus of the species; so these-both man and animal-are called secondary substances. (2a 11-17)

If we pay attention, the philosopher here distances himself from one of his favorite procedures, that is, he does not begin the discussion on substance by defining it or considering the existing opinions on the subject.³ Being a notion with philosophical content that had been under discussion for only a short time, there were probably no authors or ideas to discuss at length, except perhaps Plato. On the other hand, Aristotle also does not offer, in this passage, a definition that allows us to understand its meaning, but refers to it negatively, that is, pointing out what it is not, or mentioning attributes that cannot be referred to it (it cannot be «present in» nor be «predicated of»).⁴ This indicates that we are dealing with a concept that is both complex and difficult to understand, thus, with one of the most discussed passages in the Aristotelian corpus.

This atypical phenomenon in Aristotelian methodology could lead us to think that ousia is an incomplete notion or that it must be reconstructed by turning to other texts of the philosopher's corpus (i.e., Metaph.). However, some authors have argued that this metaphysical notion is complete and finished, and that what is expressed in Cat. coincides with his accounts in other works.⁵

On the other hand, this methodological anomaly could lead us to think that this notion is not definable, or that it exists beyond our comprehension, or that it does not exist at all. However, in 2a 34, Aristotle states that, if the ousia did not exist, nothing else would exist; and since we can confirm the existence of the world, we can confirm the existence of the substance. Some contemporary philosophers of mind have unsuccessfully tried to solve this problem by offering various linguistic and hermeneutical maneuvers, which only obscure the matter, deviating from the original Aristotelian conception. Medieval attempts, in turn, do not help its understanding either, as they tend to assume that "there is something to which [essentia and substantia] belong or from which they exist as a property, which can be identified as a substratum or base element" (^{Athanasopoulos, 2010}, pp. 217-218).⁶ After speaking negatively about substance, Aristotle gives some examples of what could be considered ousia and mentions things like «this man» or «this horse», which are individual particulars (tode ti: 'a this') that have no parts and are one in number (2a 16). Genus and species are not ousiai in a primary sense, so he considers them secondary ousiai. Furthermore, he adds that the species is closer to the particular tode ti than the genus (2a 14-19).

To understand how Aristotle conceived the role and importance of substance in his ontology, we must try to elaborate it from the non-definitional characterization he developed. In Cat. we find a key idea: ousiai are the underlying subjects (hypokeimenon) to other things. Now, in order to distinguish an underlying subject from a property or characteristic, the philosopher resorts, in Cat. 2, to predication. In simple terms, for something to be an object, one must be able to predicate things about it. If one cannot predicate things of it, but it itself must be predicated, then that something is a property. We have, on the one hand, objects, which are the subjects of predication and, on the other hand, properties, which are that which is predicated. Now, of this predication, there are two types: (a) when the predicate is inherent to the subject, in which case it receives the name of «essential predícate», and (b) when the predicate is simply in the object, in which case it is referred as «accidental predicate».⁷ Thus, when we encounter some item of reality, we must ask ourselves whether it is predicable of some object, either essentially or accidentally. If it is not possible to predicate it, it is an ousia and is understood as existing in itself and as a particular object of predication.

Another characterization that Aristotle introduces in Cat. is the understanding of ousia as tode ti, which, in turn, he associates with being indivisible and one in number:

Every substance seems to signify a certain 'this' (tode ti). As regards the primary substances, it is indisputably true that each of them signifies a certain 'this'; for the thing revealed is individual and numerically one. But as regards the secondary substances, though it appears from the form of the name-when one speaks of man or animal-that a secondary substance likewise signifies a certain 'this', this is not really true; rather it signifies a certain qualification (poion ti)-for the subject is not, as the primary substance is, one, but man and animal are said of many things. (3b 10-18)

It is evident from this passage that for the philosopher being a «this» and being «individual» and «numerically one» are related when it comes to the first substances. On the other hand, when it comes to the second substances, he does not speak of tode ti but ofpoion ti, that is, a «certain qualification», since they are said of many things. Thus, one of the qualities of the substance is to be a tode ti of which properties are predicated, but the substance itself is not the subject of any predication, since it can exist by itself, nor can it be divided into different parts and is a unity distinct and separate from other substances (this horse or this man).

For our purposes, what has been said so far will suffice to give us an idea of the concept of ousia in Cat. In the next section we will see how Aristotle brings these notions into Metaph. and introduces them within an ontological description of reality, again addressing the problem of substance.

2. SUBSTANCE IN METAPHYSICS Z

After Cat., the work that pays the most attention to the problem of ousia is Metaph. This topic has been the focus of numerous works in recent decades.⁸ There is, today, some agreement on what substance is, specifically in book Z, where the philosopher proposes the substantial forms as the ousiai par excellence.⁹ However, there has been an intense debate as to whether these forms of sensible objects are universal or particular. We will briefly review this debate from some of its exponents, and then review it critically.

At the beginning of Metaph. Z(1028a 10-12) Aristotle proposes two requirements for substance: it must be tode ti (a certain this) and ti estin (what is). As already mentioned, the requirement of being tode ti appears already in Cat. and implies that the ousia is particular, since the universal is poion ti (certain qualification) (3b 10-18). However, when he sets as a requirement that it must be ti estin, he comes closer to a universalist view of substance since, on the epistemological level, in the question of ti estin, the most cognoscible things are, by definition, universal. From this point on, a wide-ranging discussion opens up about the particular or universal nature of ousia.

Let us begin by addressing the universalist view of substance, which is the most traditional and widespread (^{Heinaman, 1979}, p. 249). Unlike the particularist view, those who defend the universality of the ousia will not find in Met. a passage where it is openly claimed that substantial forms are universal. This idea is concluded from some key passages. In Z 11 (1036a 26-29) he states that knowledge and definition are of the universal.¹⁰ If we want to affirm that ousia is susceptible of being known and defined, it must be universal. Moreover, in Z 15 (1039b 27-29) he clearly holds that there is no knowledge, definition, or demonstration of particulars.

The universalist view of ousia, then, can be summarized in four fundamental ideas:

(1) that Aristotle recognizes only one substantial form for each infima species, (2) that these species-forms are the first substances of Metaphysics Z, (3) that these species-forms, being common to each individual of their respective species, are universal, and (4) that matter is the principle of individuation (or pluralization) in the sense that it is that which distinguishes co-specific individuals (sharing one and the same form) from each other. (^{Whiting, 1991}, p. 608)

As is evident, this view considers ousia as universal, that is, as a form shared by all individuals of the same species, and whose differentiation occurs at the material level. There are, of course, different variants within universalism. Some authors defend some of these four ideas more tenaciously than others, just as other academics do not assume them all, but abandon those which seem weaker to them. Galluzzo, for example, mentions that, for universalists, the Aristotelian sentence of Z 13 (1038b 9), which denies that a universal can be a substance "does not refer to forms, but to other kinds of universals, for example, species and genus" (2013, pp. 212-213), so that Aristotle would not be referring to universals as such, but only to some of them.¹¹ On the other hand, among those who support this view, although they all address Metaph., especially book Z, some resort to other texts to give support to their understanding of substance.¹²

On the other hand, the particularistic approach to substance finds in the aforementioned passage of Z 13 its clearest pillar:

For it seems impossible that any universal term should be the name of a substance. For primary substance is that kind of substance which is peculiar to an individual, which does not belong to anything else; but the universal is common, since that is called universal which naturally belongs to more than one thing. Of which individual then will this be substance? Either of all or of none. But it cannot be the substance of all; and if it is to be the substance of one, this one will be the others also; for things whose substance is one and whose essence is one are themselves also one. (1038b 9-15)

This passage outright eliminates the possibility of ousia being universal. It is impossible for something to be tode ti (denoting the particular) and, at the same time, to be universal (said of many). Given its very nature, it cannot be said of the universal that it is one in number (Cat. 2 16). This passage seems to indicate that it is more appropriate to understand the substantial forms as particulars. Moreover, several particulars cannot share the same form without sharing the same essence; and if this happens, we are not speaking of two different things but of one and the same thing. Also, following this passage, Aristotle mentions that "substance means that which is not predicable of a subject, but the universal is predicable of some subjects always" (Metaph. 1038b 15-16). That is, if a requirement of substance is «being in itself» (Cat. 2a 11-12), it is evident that the universal, which «is always said of some subject» does not fulfill it, so it cannot be ousia. In other words, if the universal is predicated of many, and the substance is not predicated of anything (but things are predicated of it), it follows that the universal does not fulfill the requirements that Aristotle himself proposes for candidates to be ousia.

Thus, it would seem that "particular forms fulfill all the criteria for being substance in Aristotelian theory since every material object has [...] its own particular form" (^{Kar, 2018}, p. 28).¹³ Form, being ousia, is the principle of unity and identity of material objects and is their substrate in spite of and through change. If we take the example of Hartman who, contrary to the classical Heraclitean sentence, argues that it is indeed possible to bathe twice in the same river because there is a unity beyond its materiality; a unity of the water, the rocks, and the organisms that live in it. The form of the river is particular, not universal. The river may change, the water may flow, the torrent may change, the rocks may move, but the essence remains; this particular river remains itself, present in spite of change. Its particular form is what allows it to keep on existing as this particular river and not another, remaining identical to itself (Hartman, 1976). In the case of Socrates and Callias, they could not be the same person, even though they belong to the same species or genus. What makes Socrates to be Socrates is his own individual essence, which belongs uniquely to him and is peculiar to him. This, moreover, makes it possible to fulfill the requirement that the substance must be «one in number». The form of Socrates is not, nor can it be, the same as that of Callias. Therefore, the essence, which is identified with the form and, therefore, the substance, cannot be universal and be different in each individual. If they shared the same form, they could not be individual beings, one in number. In other words, if it is predicated of many, it can no longer be one in number and could not be ousia. Aristotle confirms this in Int. "Now of actual things some are universal, others particular. I call universal that which is by nature predicated of a number of things, and particular that which is not; man, for instance, is a universal, Callias a particular" (17a 38-17b 2).

What has been said so far suffices to show the central arguments of the particularist position on substance. With what has been presented so far, the universalist vision, although interesting and suggestive in some points, appears to us as incompatible with the ontological structure that the philosopher attributes to reality and to the requirements that he sets for something to be substance. However, the particularistic approach is not free of difficulties and must solve some problems of its own, which we will analyze in the following section.

3. THE EPISTEMOLOGICAL PROBLEM OF PARTICULARISM

The main problem this approach faces lies at the epistemological level. In Aristotle's theory of knowledge, definition, demonstration, and cognizability correspond to the universal.¹⁴ At the beginning of Metaph. Z, Aristotle says of substance: "Now, «first» is said in several senses; but in all substance is first: as to the statement, as to knowledge, and as to time" (Z 1, 1028a 32-34). Thus, if it is claimed that substantial forms are of a particular character, true knowledge about them would not be viable. This makes it incompatible as a candidate for ousia. In the face of this difficulty, various solutions have been offered.

Whiting mentions the common formula of "denying that Metaphysics retains the commitment of Categories about the priority of individual substances over the class to which they belong" (1991, pp. 614-615). This could imply that Aristotle inverts in Metaph. what is exposed in Cat. i.e., that the species is prior to or has priority over the individuals. Thus, Metaph. would turn out to be a kind of return to the Platonism against which Cat. would have rebelled. However, Whiting recognizes, this brings us back to the problem that no universal can be ousia (1991, p. 615). Moreover, this reasoning challenges an argument proper to particularism, namely, that the individual substances in Cat. are replaced in Metaph. by the substantial forms as first substances.¹⁵ As we shall see, Whiting offers another solution which she considers more adequate.

A second option is offered by various authors and proposed in different ways: the cognoscibility of particulars, far from being impossible by their very nature, is given to them by their relation of interdependence with universals. If the substance is the most real, but the universal is the most cognoscible, how does one solve the problem of the less real being more, or equally, cognoscible than the most real? (^{Kar, 2018}, p. 142). Leszl regards this problem as a «serious logical-epistemological difficulty» and offers the following solution: knowledge of particulars becomes possible to the extent that they are instantiations of universals. In this way, substantial forms can retain their particularity and, at the same time, fulfill the epistemological requirement of being cognizable, just as universals are, since what is said of the universal (definition), would also be said of the particular (Leszl, 1972, pp. 281-282). Baylis explains it as follows:

The existence of communicable knowledge requires shared meanings. Knowledge of this kind, in its simple form, is knowledge of the common characteristics exhibited by various objects and events. In the most advanced form of scientific knowledge is knowledge of the interrelationships of those characteristics in all their possible instantiations. (^{Baylis, 1970}, p. 50).

Frede, in turn, although he does not mention it explicitly, offers a variant of this solution: if what individualizes each particular is matter,¹⁶ and this permanently changes, how can we recognize a particular form at two different times, when its matter has changed? And he says: "it can be identified through time by its continuous history of being realized now in this matter and then in that other matter, of being the subject of these properties and then being the subject of those other properties" (Frede, 1987, p. 78). That is, he recognizes that the particular is not susceptible of being recognized as a particular, but because it is «realized» here and there. In other words, given its interdependence with the corresponding universal and given that it is an instantiation or «realization» of the latter, it is possible to know and recognize it.

Irwin, in turn, also takes part in this solution to the problem of the cognizability of particulars:

Aristotle cannot, for the reasons we have just seen, admit that the particular is, in itself, the object of definition and scientific knowledge; but he can still reasonably insist that scientific knowledge and definition apply to particular forms. A particular man is, essentially, a particular form, which is an instance of the universal species-form and, for this, our scientific knowledge applies to the particular. (1991, p. 263)

Like Frede, Irwin recognizes that the particular, as a particular, is incapable of fulfilling the Aristotelian epistemological requirement. However, if it is understood as a case of the universal, its properties of cognoscibility are transferred to it and its knowledge becomes possible.¹⁷ Thus, the particular form succeeds in fulfilling the requirements of substance, namely, to be tode ti, one in number and, moreover, being open to be known.¹⁸

Whiting, as we mentioned, offers another solution to this problem by resorting to a distinction that, from her perspective, is fundamental and settles the discussion: Aristotle denies the possibility of knowledge of material particulars, not of particulars per se. This distinction implies establishing a difference between the so-called «particulars» and «individuals». For the author, this distinction is based on the language used by Aristotle himself to refer to one and the other. The individuals represent the use of hen arithmoi (one in number), while the particulars are referred to with the use of kath 'hekaston. This distinction is clear, for example, when Aristotle "grants that the Prime Motor (which is immaterial and imperishable) is one in number (1074a 36-37) but says that this place is proper or peculiar (idios) to particulars (1092a 18-20), thus suggesting that a particular is a kind of individual, namely, a material one" (Whiting, 1991, p. 609). In this way, true knowledge of particulars is possible, since the epistemological limit is attributed to material individuals, not to particulars qua particulars. Finally, Whiting cites Z 15 and Rh. 1356b 29-33 and insists on the idea that Aristotle there "argues [...] only against the knowledge ofparticulars (i.e., material individuals) and not against the knowledge of individuals as such" (Whiting, 1991, p. 614).¹⁹ Albritton offers another variant of this solution, but understanding instantiation in a slightly more obscure way. From a series of passages in Metaph. Z and H, he claims that instantiations operate as follows: "a particular material substance not only shares with others of the same species a universal form, but also possesses a form of its own, an instance of that universal form, which is not the form of anything else" (Albritton, 1957, p. 700). Thus, the particular form would be tode ti and one in number by its individuality and, at the same time, cognizable by its relation to the universal form. To explain this, he offers the following example: "Suppose the species is sphere and its form the universal, sphericity: the thing is a sphere, and its particular form a sphericity, i.e., its sphericity" (Albritton, 1957, p. 701). This way of approaching the problem, however, evidently assumes the existence of two forms, and seems to be closer to understanding form as an entity rather than as a principle of entity. Thus, although interesting, this approach to instantiation seems to differ too much from its other variants, making it virtually unable to solve the issue.

4. SUBSTANCE IN THE DE ANIMA

As is well known, the De an. is not a metaphysical treatise on reality; rather, it focuses on one specific aspect of reality, i.e., the soul and its faculties. However, when approaching the problem of the definition of the soul in book 2, Aristotle gives certain clues as to what may allow us to clarify the problem of substance. In 2.1 he argues:

We say that among the things that exist one kind is substance, and that one sort is substance as matter, which is not in its own right some this; another is shape and form, in accordance with which it is already called some this; and the third is what come from these [...] It would follow that every natural body having life is a substance, and a substance as a compound [...] It is necessary, then, that the soul is a substance as the form of a natural body which has life in potentiality. (412a 6-21)

At first glance the reader notices that the philosopher picks up the discussion that takes place in Metaph. Z on the best candidate for substance (1042a 26-31) and seems to take its conclusion for granted, for he does not bother to explain it, but assumes his audience's familiarity with it. In this passage he employs all the senses of ousia: the matter, the compound, and finally the form, which, for the purposes of his psychology, is the soul. In the final lines of the quoted text -which correspond to the first definition of the soul- he explicitly states that the soul corresponds to an ousia in the sense of a form (hos eidos). Thus, there is little doubt about the linearity between De an. and Metaph. on the way in which he understands form as ousia. With this prior clarification, we can enter into other passages of the treaty to determine whether the soul is considered as particular or universal.

Let us review a crucial passage, found in 1.3:

These accounts merely endeavour to say what sort of thing the soul is without articulating anything further about the body which is to receive the soul, as if it were possible, as according to the Pythagorean myths, for just any soul to be outfitted in just any body. For each body seems to have its own peculiar form and shape. (407b 20-24)

Here the philosopher is explicit in criticizing those -the Pythagoreans- who maintain in their myths that any soul would be suitable for any material body. This is the famous theory of the transmigration of souls that Plato picks up later from the Pythagoreans. Aristotle argues against this notion by pointing out that the union of body and soul is specific and particular. This means that there is one soul for each body and one body for each soul. This understanding of the union of body and soul is, moreover, consistent with the hylomorphic theory that he applies in De an. and that he employs to his entire understanding of the nature of the soul and to the analysis of its faculties, especially perception and intellect.²⁰ It could be said that the philosopher is not referring here to the specific union of body and human soul, but is alluding to the types of soul (nutritive, sensitive and intellective) and that they can only be realized in a body apt to deploy those powers. While this criticism seems to make sense, it is implausible since the levels of life appear later in book 2 and have not yet been presented. Thus, that Aristotle is assuming a psychological structure of nature that he has not yet shown or explained makes little sense within the narrative of the work. It is much more feasible to think that he is indeed referring to the specific union of human body and human soul.

We have previously mentioned that one of the difficulties of the particularistic approach to substance is the incapacity we would have to know it in a definitional way. An argument in favor of this problematic -and which reinforces the idea of the soul as a particular and not a universal item- is that Aristotle, in fact, does not offer a definition of the soul stricto sensu, but rather a characterization. The problem of supposed definitions of the soul is long-standing and amply documented.²¹ The fact that the philosopher does not provide a definition of the soul may be due, among other things, to the impossibility of doing so, precisely because it is a particular and not a universal.

Despite this, some authors have tried to argue that the soul is universal and that it is not a particular notion. It is Aristotle himself who recognizes that, although Socrates and Callias may be different in virtue, they are the same in form (eidos) (Metaph. 1034a 5-8).²² By definition, a universal is said of many (legetai pollachos) or is predicated of several particulars. In this case, Socrates and Callias are not one and the same as individuals, but as a species. Moreover, if one follows the idea that the principle of individuation is matter, Socrates and Callias would be different as to it, but not as to their form. On the other hand, in Metaph. Z 7 Aristotle discusses the origin of forms and relates it to his naturalism. In the case of the generation of human beings, if each person had a unique form: from where is it given to him? What is the process of generation of these individual forms? The most appropriate, for universalists, is to think that at the moment of generation the person somehow receives a pre-existing form common to all. This has led some contemporary scholars to argue that there is a single universal soul-form, shared by all human beings and which gives them their essential properties, being individualized only by the matter-body (^{Galluzzo, 2013}, 213-124).

In the same vein, ^{Lear (1994}, p. 308) points out that there is but a single soul animating bodies that are numerically different. This reading of the idea of soul in Aristotle is extremely counterintuitive; no passage in the whole De an. allows us to think that there is only one soul for all living beings or, more specifically, for all human beings. On the contrary, if we pay attention to the quoted passage, the philosopher is explicit in saying that the union of body and soul is specific, which implies that there is a different soul for each specific living being. Just as those living beings possess specific bodies, they also possess souls specific to those bodies. If we take, in short, the problem of the universality or particularity of substance from Aristotelian metaphysics to the field of psychology, the most plausible conclusion seems to be only one: my soul is mine and mine alone.

CONCLUSION

The purpose of this paper was to develop an analysis of the universalist and the particularist positions on substance, as presented by Aristotle in his Metaph. At first, we posed the problem from the first text in which the notion of ousia appears, namely Cat. This was followed by a brief account of the universalist and the particularist views of substance. And finally, an attempt was made to offer a solution to the main problem of understanding substance as particular.

We were able to note that each view faced its own problems. On the one hand, universalism must deal with two main obstacles: first, explaining how substance can be universal and fulfill the requirement of being tode ti (and not poion ti) and, second, how to understand the passage quoted from Z 13 where Aristotle holds that no universal can be substance. Particularism, on the other hand, must solve the problem of the cognoscibility of substance, i.e., explain how substance can be particular and, at the same time, be cognoscible and definable. From what has been exposed throughout the text, it seems that the particularist view has better grounds to sustain itself and is better aligned with Aristotelian sources, specifically with the requirements established by the philosopher for substance, that is, to be a certain this, one in number, that which is, and to be epistemologically apprehensible. On the other hand, in this paper we have intentionally omitted those authors who, instead of assuming one position or the other, seek to demonstrate that either both are true and substance is, in turn, universal and particular, or that both are false insofar as they do not allow a complete understanding ofthe role played by substance in reality under the Aristotelian view.

Finally, an attempt was made to shed light on this problem in its application to psychology. In De an. Aristotle makes a clear and explicit defense of the particularity of the soul-form, so that there would not be many or solid reasons to think that it is a universal principle.²³ Thus, although the discussion on substance seems to move on the field of metaphysics and the structure of reality, when we apply it to other disciplines, the matter seems to become clearer. We thus conclude that when it comes to the soul as form, there is little doubt that we are dealing with a principle of a particular character.