2. Thomistic approaches to matter and essence

In the Thomistic tradition, an entity is considered a being (ens) in virtue of its act of existence (actus essendi), and a thing (res) according to its essence under the aspect of quiddity (essentia qua quidditas).Footnote ³ In all things apart from God, existence is distinguished from essence qua quiddity.Footnote ⁴ Yet, they remain connected, since every entity has being (ens) in virtue of its existence (esse), which comes in and through its essence qua quiddity.Footnote ⁵ It is according to the same essence qua quiddity, by which an entity is considered a thing, that it is named as a particular type of thing.Footnote ⁶ Consequently, the identity of an entity depends upon the essence qua quiddity in and through which it has existence.Footnote ⁷

To elucidate the tension between survivalists and corruptionists, consider the example of a living human being, Socrates. As an entity, Socrates is considered a being in virtue of his act of existence, and a thing according to his essence under the aspect of quiddity. The act of existence by which Socrates is considered a being is in and through Socrates’ essence qua quiddity. It is according to the same essence qua quiddity that Socrates is called a human being (homo). After his death, the soul of Socrates subsists apart from his body. Unlike the substantial forms of other material objects, the human soul of Socrates is considered a being, since it retains an act of existence apart from the body after death.Footnote ⁸ Additionally, Socrates’ soul is a thing because it has an essence qua quiddity, in and through which it has an act of existence. What is disputed is whether the essence qua quiddity of the human soul remains identical to that of the human composite, with the answer having considerable implications for whether the separated soul continues or ceases to be the existence of a human being in any ontologically meaningful way.

Survivalists have typically argued that the subsisting soul is the partial existence of a human being. On this view, the soul remains a being that has an act of existence in and through an essence, and that essence contains the essential principles of the human species. They concede that the soul’s mode of existence is imperfect, since the soul’s substantial existence is only immaterial. As a result, the soul does not constitute the existence of a whole human being, whose ordinary mode of existence is as a composite of both soul and matter. However, since the essential principles of the soul remain identical to the essential principles of the composite human being, the soul’s essence qua quiddity remains human. The subsistent soul and human composite differ in categories of existence, not essence qua quiddity. Consequently, the soul survives death as the partial existence of a human being, lacking the substantial and accidental perfection of its human essence.Footnote ⁹

Some corruptionists have challenged this reading on metaphysical grounds. They argue that the essence of the soul changes after its separation from the body, so that it no longer constitutes even a partial human existence; it ceases to be a human existence altogether. Prominent corruptionist Turner Nevitt argues that, since corruption involves the loss of material existence, and matter is part of the human essence, the soul alone cannot have a human essence. Furthermore, he contends that because the essence of a thing is strictly necessary for its existence, and it cannot be anything other than its essence, the soul, apart from the body, cannot be constituted by the essence of a human being, and thus the subsistent soul ceases to be the existence of a human being.Footnote ¹⁰ Put another way, while the soul retains being according to an act of existence in and through an essence, that essence ceases to have the essential principles of a human being since it loses its matter at death. And so, the soul’s act of existence ceases to be in and through a human essence. Consequently, the quiddity of the soul changes so that it can no longer be said to be the existence of a human being in any real metaphysical sense.Footnote ¹¹

Both the survivalist and corruptionist positions accept that matter belongs to the essence of human beings, since Aquinas is unambiguous about this in De ente et essentia.Footnote ¹² Where they differ is whether the loss of the material body at death necessitates a change in essence. The corruptionist approach to essence interprets the loss of the material body as requiring a change in essence. If correct, it would significantly undermine the survivalist’s position as an interpretation of Aquinas.Footnote ¹³ Yet, this paper defends the survivalist account by clarifying how Aquinas attributes matter to the essence and demonstrating that the loss of the body does not cause an essential change in the soul.

3. Aquinas’ three aspects of essence

Central to the discussion at hand is Aquinas’ account of essence and whether it differs between the composite and the separated soul. What complicates the concept of essence is that it is used in different senses. In De ente et essentia, Aquinas notes three ways that the essence might be approached. These ways can be distinguished as follows: (1) essence qua nature, as understood by the intellect through a thing’s accidental operations; (2) essence qua form, as it is actualised in the individual; and (3) essence qua quiddity, that by which a thing is a particular thing.Footnote ¹⁴ While the three ways of approaching the essence are conceptually rather than really distinct, attending to the differences between these aspects will highlight which are relevant to predicating things of the essence and thus how it is that Aquinas attributes matter to essence.

First, essence qua nature refers to the essence of a thing as grasped by the intellect.Footnote ¹⁵ The intellect comes to know a thing’s nature by abstracting from sensory impressions, or phantasms, which, once understood, can be expressed in the form of a word or a definition.Footnote ¹⁶ For this reason, Aquinas states that a thing’s definition signifies the essence.Footnote ¹⁷ However, this aspect of essence only signifies the essence of a thing as it is ordered towards its proper operations. For Aquinas, a human being belongs to the species ‘humanity’, which, in turn, belongs to the genus and differentia of ‘rational animal’.Footnote ¹⁸ In turn, ‘rational animal’ designates the kinds of operations that human beings can perform,Footnote ¹⁹ its powers and operations. However, since these are only accidental to the essence, a term such as ‘rational animal’ can only signify the essence indirectly.Footnote ²⁰ This is because, for Aquinas, essential differences, like forms in general, are unknowable directly,Footnote ²¹ and so are signified through accidental differences as causes are signified through their effects.Footnote ²² While this makes a thing actually intelligible, what is contained in the intellect is not the essence itself, but the essence as abstracted from accidental operations.

Second, essence qua form refers to the essence of a thing as it is actualised by form. Aquinas observes that essence is understood in this way because ‘the certitude of every thing is signified through its form’.Footnote ²³ This aspect of essence follows Avicenna’s distinction between nature, which refers to a thing with respect to its motions and actions, and form, which has the power to ensure that any actualised matter is constituted as a particular species.Footnote ²⁴ When Aquinas attributes form as the certitude of every thing, he makes a similar assertion that form makes an existing subject what it is and maintains it as that thing by actualising the essence in that substance.

The third aspect is essence qua quiddity. This highlights the essence as it describes what it is to be a thing, that by or through which ‘something has being as a particular kind of thing’.Footnote ²⁵ While the previous concepts approach the essence through its operation or its actualisation, this aspect directly describes a thing’s whatness. This aspect of essence relates to a thing’s operations as a cause relates to its effects.Footnote ²⁶ It can also be understood as the internal principle responsible for a thing’s properties,Footnote ²⁷ as well as ‘species-specific potentiality’,Footnote ²⁸ or ‘inherent capacities’.Footnote ²⁹ It is this aspect of essence that is considered apart from existence in all things but God.Footnote ³⁰

As noted above, an entity is considered a being in virtue of having some act of existence, which comes about in and through its essence qua quiddity. Aquinas’ threefold account of essence highlights why a thing has existence in and through essence qua quiddity, rather than essence qua form or essence qua nature. Both essence qua form and qua nature describe the essence as it has some existence. The former describes the form’s role in ensuring an existing substance is a particular species, while the latter expresses a thing as it is understood by the intellect via abstraction. Since these two types of essence already enjoy some mode of existence, they cannot be the aspect of essence in and through which the act of existence comes. Therefore, in Aquinas’ account, essence qua quiddity is the aspect of essence in and through which an entity’s act of existence comes.

4. The double meaning of names and species-predicates

Having outlined Aquinas’ account of essence, it is worth commenting upon how Aquinas attributes names and species-specific predicates to entities. In Sententia super Metaphysicam, Aquinas highlights that the name of a species, such as human being (homo), can be derived from either its nature or its quiddity.Footnote ³¹ Additionally, in De spiritualibus creaturis, he notes that things predicated of a species, such as ‘sensible’ or ‘rational’, can either be differences derived from a thing’s powers or from differences in the essence of the soul.Footnote ³² The naming of a species and the attribution of predicates to a species share in common that they can refer to either a thing’s accidental operations, and thus describe a thing according to the essence qua nature, or to a thing’s essence qua quiddity.

Attributing names or predicates to an entity according to its essence qua nature is more natural to human beings, since the object of the intellect is not essence directly, but rather the essence as it exists in corporeal matter,Footnote ³³ abstracting predicates from determinate parts.Footnote ³⁴ Aquinas notes that ‘[s]ubstantial differences being unknown to us, or at least unnamed by us, it is sometimes necessary to use accidental differences in place of the substantial … for proper accidents are the effects of substantial forms, and make them known’.Footnote ³⁵ Understood in this way, when Socrates is named a human being (homo), and human beings are defined by predicates such as ‘sensible’ or ‘rational’, it is according to the observable accidental operations which are cognised by the intellect. For instance, one may observe Socrates operating his senses by looking around the room or smelling flowers, or recognise his rationality through his verbal explanation of complex ideas.

Names and predicates can also be derived from and attributed to the essence qua quiddity directly. Given that quiddity is void of any existential act, when a name or predicate is attributed to an entity in this way, it is not referring to any observable accidents that signify the essence. Instead, when names and species-predicates refer to the quiddity of a thing directly, it refers to the essence as the principle that can give rise to particular properties. Taken in this sense, when Socrates is named a human being (homo), or the human species is defined as ‘sensible’ and ‘rational’, it refers to essence qua quiddity as the principle that can give rise to a certain type of existence, with the predications delineating the properties that Socrates’ essence qua quiddity can give rise to.Footnote ³⁶

5. Implications for Aquinas’ account of matter

Having outlined Aquinas’ account of essence, and the way that names and species-predicates can refer both to the essence qua nature and qua quiddity, it is now possible to analyse how he attributes matter to the essence of composite things. Although the corruptionist account outlined above treats matter as a unitary category, Aquinas has three types of matter that can be attributed to human beings in some sense: prime matter (materia prima), designated matter (materia signata), and non-designated or common matter (materia communis).

In Aquinas’ account, prime matter is that which is in a state of pure potency to substantial being. Pure potency implies that it has no active powers, no determinate quantity, and no actual existence in the world apart from form.Footnote ³⁷ As Aquinas notes, since ‘all knowledge and every definition comes by the way of the form, prime matter cannot be defined or known in itself but only through the composite’.Footnote ³⁸ Some, such as Jeffrey Brower, read this ontologically, arguing that prime matter is best understood as ‘non-individual stuff … a distinctive type of being that is infinitely divisible and incapable of existing apart from material substances’.Footnote ³⁹ Others, such as Robert Pasnau, read this ideologically, arguing that prime matter functions as a necessary metaphysical principle that highlights that ‘through substantial change, [material substances] can, eventually, become any sort of body’.Footnote ⁴⁰

In either sense, prime matter is generally considered to lie outside the essence qua quiddity.Footnote ⁴¹ As Joseph Bobik notes, the essence under the aspect of quiddity must furnish an answer to the question ‘what is it?’.Footnote ⁴² Taken ontologically, prime matter is excluded from the essence qua quiddity since it lacks any definition per se apart from form. Considered of itself, then, it lacks any quidditative content. Therefore, it would be a category mistake to include prime matter per se in the essence qua quiddity, since it does not contribute to grounding a thing’s identity or definition. The same can be said of the ideological view, since prime matter merely highlights that material substances can become any other type of body. It does not provide any quidditative content that defines what a thing is. Therefore, taken in either sense, prime matter lacks the definitive role that the essence qua quiddity requires.

Designated matter is the specific matter of the individual. Aquinas notes that this type of matter exists under ‘determinate dimensions’,Footnote ⁴³ or as Patrick W. Hughes states, it is ‘the matter that is existent in the world and is readily apparent to us’.Footnote ⁴⁴ In contrast to prime matter, it has a definition and is intelligible. But while this type of matter has a definition, it does not belong to the human species. Instead, Aquinas affirms that one can only predicate designated matter of individuals, forming part of the definition of Socrates, if he had such a definition.Footnote ⁴⁵ For Aquinas, human beings do not have the same designated matter: Socrates’ flesh and bones differ from Plato’s flesh and bones. If it were the case that designated matter belonged in the definition of humanity, then it would be impossible for there to be more than one person in the human species.Footnote ⁴⁶ Instead, designated matter acts as the principle of individuation,Footnote ⁴⁷ by which a species has multiple members.Footnote ⁴⁸ Consequently, since designated matter is attributed to the individual, and not to the species, this type of matter cannot be attributed to the essence qua quiddity of the human species. Thus, although designated matter is lost at death, and this loss entails the dissolution of Socrates’ composite existence, it does not alter the individual’s essence qua quiddity that is considered apart from a thing’s existence.

Common matter (also called non-designated matter) is that which Aquinas explicitly associates with the human species.Footnote ⁴⁹ One way of understanding common matter is to consider what is common to the species that is not predicated of the individual. For example, Socrates and Plato are both human beings who belong to the species humanity. Since they have different bodies, designated matter cannot be predicated of the species; otherwise, it would only be possible to have one member of humanity. But they can both be described as having some material existence. As Aquinas states, ‘[i]n the definition of man … is included non-signate matter: in the definition of man we do not include “this bone” and “this flesh” but only bone and flesh absolute, which are the non-signate matter of man’.Footnote ⁵⁰

At this point, it is worth drawing on Aquinas’ double meaning of species-predicates. Since common matter is predicated of the human species, it can either refer to the essence qua nature or qua quiddity. When understood as referring to a human being’s essence qua nature, common matter can be seen as referring to the various proper accidents that arise from material existence (e.g. quantity) in a similar way to how ‘sensible’ refers to multiple proper accidents that arise from a thing’s existence as a sensitive being (e.g. sight). At death, these accidents cease to exist on account of the separated soul. As such, common matter cannot be attributed as a species-predicate of the subsistent soul’s essence according to observable accidental operations, since the soul ceases to produce operations that have a sensible impression and thus ceases to be the subject of the intellect’s process of abstraction.Footnote ⁵¹ And if this were the only way one could predicate common matter of a thing’s essence, the corruptionist would be right to assert that death causes both the cessation of all material categories (prime, designated, and common matter) and that this indicates an essential change in the soul.

However, species-predicates can also refer to a thing’s essence qua quiddity even when they cannot be established from the essence qua nature. As noted above, the essence qua quiddity refers to the internal principle responsible for a thing’s properties, with the result that the attribution of species-predicates delineates the capacities that a thing’s essence qua quiddity can produce. For example, when ‘sensible’ is predicated of the essence qua quiddity, it refers to the essence of the soul as being the root or principle of the sensitive powers in the individual.Footnote ⁵² When such powers cease to exist after the soul’s separation from the body, the soul continues to be the root or principle of these powers.Footnote ⁵³

Although Aquinas’ account of common matter is underdeveloped,Footnote ⁵⁴ it shares analogous features to this example. Common matter is explicitly predicated of the human species by Aquinas.Footnote ⁵⁵ As a species-predicate, it refers to a thing’s essence qua quiddity. Aquinas makes this explicit in Sententia super Physicam, where he outlines how definitional constituents of the species pertain formally to individuals:

This extended quotation makes clear that it is common matter, rather than individual matter, that is predicated of the species. But more importantly, it articulates an important principle: that all predicates of the human species, whether these are predicates like ‘sensible’, ‘rational’, ‘living’, and even ‘form’ and ‘common matter’, pertain to the formal cause or, as the broader context of this passage makes clear, the essence qua quiddity of the individual.Footnote ⁵⁷

Since Aquinas attributes common matter to the human species, and then explicitly relates it to the essence qua quiddity of individuals, it follows that common matter must delineate some determinate mode of actualisation in the individual for which the essence qua quiddity is the principle. As noted above, common matter refers to flesh and bones absolutely, rather than this flesh and these bones. Therefore, by logical extension, when common matter is predicated of a thing’s essence qua quiddity, it should be understood as referring to the essence of the soul as being the principle of flesh and bones in the individual, or more straightforwardly, the individual’s material existence.Footnote ⁵⁸ While Aquinas does not characterise common matter directly in this way, it follows as a conclusion from Aquinas’ treatment of other species-predicates, even if he does not draw out the implications of attributing common matter to an individual’s quiddity explicitly.

That common matter refers to the essential principle of an individual’s material existence is supported by Aquinas’ affirmation that such a principle exists in the essence of the soul after death in a similar manner to how the soul remains the principle or root of the sensitive powers. He notes ‘[t]o be united to the body belongs to the soul by reason of itself … so the human soul retains its proper existence when separated from the body, having an aptitude and a natural inclination to be united to the body’.Footnote ⁵⁹ Furthermore, he notes that ‘[t]he body is not of the essence of the soul; but the soul by the nature of its essence can be united to the body’,Footnote ⁶⁰ and ‘it is essential to the soul that it be the form of a body’.Footnote ⁶¹ The pattern seen across Aquinas’ writings is that the separated soul retains an essential proclivity to be united to a body. In fact, it is the soul’s ability to be united to a body that distinguishes human souls from angelic beings.Footnote ⁶² Consequently, common matter, as it describes the essential principle of an individual’s material existence, persists in the essence of the soul after its separation from the body, explaining why the subsistent soul has an irreducible orientation towards bodily union.

Returning to the question at hand: does death necessitate the cessation of the material categories relevant to the essence qua quiddity, so that the separated soul undergoes an essential change? It has been established that neither prime nor designated matter pertains to the essence qua quiddity, with the result being that their loss at death does not cause an essential change. But Aquinas does explicitly connect common matter with the essence qua quiddity, with the result being that any change in this material category would imply a change in the soul’s essence. However, on this interpretation, common matter, defined by Aquinas as flesh and bones absolutely considered, relates to an individual’s essence qua quiddity as being the essential principle of material existence. This persists in the essence of the soul, as demonstrated by the soul’s natural proclivity towards material existence apart from the body. In light of this analysis, Aquinas’ attribution of matter to the essence of composite things in De ente et essentia should be understood as referring to common matter. But since common matter does not refer to any actually existing matter but instead denotes an individual’s essential principle of material existence, the subsistent soul continues to retain the category of matter which Aquinas attributes to the essence of composite things.Footnote ⁶³

6. Essence, matter, and the imperfect survival of the human soul

To take stock, on Aquinas’ account, essence can be considered under the aspect of nature, form, or quiddity. Essence qua nature and qua form include some type of existence, with essence qua quiddity being the only aspect that does not include any existence. Thus, it is in and through the essence qua quiddity that an entity receives its act of existence, in virtue of which it is considered a being. Additionally, it was noted that the name of an entity and predicates that are placed in the definition of a species can refer to the essence as it is abstracted from observable accidental operations (essence qua nature), or to the essence as being the root or principle of those operations (essence qua quiddity). Finally, in considering Aquinas’ account of matter, it was shown that neither prime nor designated matter pertains to the definition of the human species. Common matter was found to be the only type of material category that could be attributed to the essence qua quiddity of human beings in Aquinas’ framework. While Aquinas does not elaborate on how common matter should be understood when applied to the essence qua quiddity of individuals, given his treatment of other species-predicates, it was established that common matter should be considered the essential principle of an individual’s material existence. That such a principle exists in the soul after death is demonstrated by Aquinas’ repeated affirmation that the separated soul retains an orientation towards bodily union.

Aquinas’ account of essence and matter exposes the central equivocation at the heart of the debate. Corruptionist positions that assert that the loss of the body at death necessitates a change in essence assume that the matter that is attributed to the essence of composite things refers to an individual’s designated matter. However, Aquinas restricts the type of matter that enters the definition of the human species to common matter and then attributes this to the internal formal cause or quiddity of individuals. Common matter persists in the soul by virtue of its essence being essentially ordered towards material existence, so that souls can be substantially united to a body rather than all such unions being accidental. This was the primary concern of Aquinas when he attributed matter to the essence of composite things in De ente.Footnote ⁶⁴ Therefore, while death strips the subject of substantial and accidental material existence, common matter continues to pertain to the essence qua quiddity of the subsistent soul.

Once this is in view, the survivalist position that the subsistent soul is the existence of a human being follows straightforwardly. After death, the soul retains the material category required to be a member of the human species, so that its essence qua quiddity remains identical before and after death. Since the names of things are drawn primarily according to quiddity, the subsistent soul’s identity remains identical to the composite: a human being (homo). The soul’s act of existence continues to come in and through its human essence qua quiddity, retaining all the principles proper to the human species. Therefore, the subsistent soul continues to be the existence of a human being in a metaphysically significant way.

While the subsistent soul’s essence is considered human, the existence of the soul is not considered the perfect existence of a human being, since it lacks the substantial and accidental perfection proper to the human species. As Aquinas notes, the subsisting soul is a part of a human being.Footnote ⁶⁵ Contrary to some corruptionist claims,Footnote ⁶⁶ partial existence does not imply a change of essence; instead, it merely implies that the soul is subject to evil: the privation of the material mode of being it ought to have according to its essential principles. For Aquinas, a thing experiences privation if there is an existence that is both lacking and can be received by a subject,Footnote ⁶⁷ and privation becomes evil if such a lack denies that which is naturally due.Footnote ⁶⁸ As Montague Brown puts it, ‘[e]vil is a particular failure of some thing to fulfil its nature’.Footnote ⁶⁹ Aquinas notes that ‘the fullness of human being requires a compound of soul and body’, and that any lack of these implies that the human being is ‘lacking in something due to the fullness of his being’.Footnote ⁷⁰ By virtue of common matter pertaining to the subsisting soul, its essence being the principle of its material existence, the soul is naturally orientated towards material existence, even though it does not inform any material body. This suggests that the soul’s separation from the body deprives it of a material existence that is naturally due to it.Footnote ⁷¹

Now, insofar as a thing is subject to evil, it lacks being proper to its perfection. Accordingly, if the subsisting soul is subject to evil, at least in the sense that it lacks substantial and accidental material existence, then this soul has an imperfect existence. This clarifies Aquinas’ claim in Summa contra Gentiles that:

His argument here does not rely on any corruption or change of the subsistent soul’s essence, but on its separation from the bodily whole to which it is naturally ordered. The separated soul is imperfect precisely because it remains human, with its essence continuing to be naturally orientated towards a bodily existence that it lacks. As such, its imperfection is not an admission of essential change, but a privation of the being it ought to have. Therefore, although the subsistent soul can survive being separated from the body, this existence is considered imperfect, since it retains all the essential principles, including common matter, by which it can attain a perfected human existence, a restoration that, for the Christian tradition, is realised in the resurrection of the body.