St. Thomas Aquinas on the Separated Soul and Its Personhood: A Mixed View

Abstract

De Haan and Dahm have recently proposed a “Middle Way” to reconcile the long-standing conflict between Corruptionists and Survivalists in the ancient Thomistic debate over the personhood of the separated soul. While the Middle Way avoids some difficulties with the traditional positions, it relies on the unstable notion of an “incomplete person.” Building on the Middle Way’s insights, this paper proposes a “Mixed View.” Based on “Single-Part-Composition”, “Composition as Non-Identity”, “the Criterion of the Numerical Identity of Substances”, and the three criteria of personhood analyzed by De Haan and Dahm, I argue that the separated soul solely composes a substance that is numerically identical to the pre-mortem substance. This post-mortem substance satisfies the criteria for personhood but no longer under the species of human being, and the soul itself is not a person. The Mixed View preserves personal continuity without attributing personhood (complete or incomplete) to the soul, while also retaining the metaphysical seriousness of death as a substantial change, the abhorrence of death and the necessity of Resurrection.

1. Introduction

According to Thomas Aquinas, an individual human being, such as Socrates, is a substance composed of soul and body (ST. I, q. 75, a. 4).1 Death of body (mors corporis) is the separation of soul from body, and resurrection is their reunion (cf. CT I. 239). After death and before resurrection, the soul exists as a “separated soul” (anima separata). Aquinas explicitly discussed the question “whether a separated soul is a person” (In III Sent. d. 5, q. 3, a. 2). The issue bears not only on philosophical anthropology and metaphysics but also on theological doctrines, biblical interpretation, and Christian practice.

Two main positions once dominated the discussion. Corruptionists deny the separated soul is a person, in line with Aquinas’s repeated statements that “the separated soul cannot be called a person.”2 Survivalists, by contrast, maintain that the soul itself is a person, often appealing to texts that describe the soul as a “this something” (hoc aliquid).3 Each view, however, faces difficulties. Corruptionists struggle to explain post-mortem reward, punishment, and the supposits of rational activity.4 Survivalists, on the one hand, often require a radical reinterpretation of numerous texts in which Aquinas explicitly supports corruptionists and risk attributing to Aquinas a form of dualism that diminishes the metaphysical role of the body and the significance of resurrection.

In response, De Haan and Dahm (2019, 2020) propose a “Middle Way”. By articulating three criteria of personhood, they argue that the separated soul satisfies these only incompletely and should be regarded as an “incomplete person” (cf. De Haan and Dahm 2019, pp. 611–30). Their account, especially their systematic discussion of the criteria of personhood, represents an important advance, especially in clarifying the structure of personhood within a Thomistic framework. It has generated substantive engagement in the recent literature (cf. Spencer 2020). Nevertheless, despite these merits, important metaphysical tensions remain unresolved.

As I see it, the continued disagreement in the literature does not stem from a lack of metaphysical resources in Aquinas. Three Thomistic principles are recognized and independently defended in the recent literature: Single-Part-Composition, Composition as Non-Identity, and the Substantial-Form-Based Criterion of Numerical Identity. Each has already been invoked in discussions of the separated soul, most systematically by Jeffrey Brower (2014, pp. 279–310), who employs Single-Part-Composition in developing a survivalist reconstruction and in addressing Christological issues. What remains insufficiently explored is how these principles jointly work in the metaphysics of the post-mortem subject when applied together and how their implications interact with the criteria of personhood.

This paper develops a Mixed View that emerges from integrating these resources. Drawing on De Haan and Dahm’s analysis of personhood and inspired by Brower’s application of Single-Part-Composition, I argue that after death and before resurrection Socrates (1) survives and (2) remains a person, yet (3) he is no longer a human person, and (4) his soul, though his sole proper part, is not itself a person. In affirming survival and personal continuity, the view converges with survivalism; in denying that the soul is a person and in emphasizing the loss of humanity, it converges with corruptionist intuitions. At the same time, it avoids the Middle Way’s appeal to “incomplete person”, which seems to be problematic.

The paper proceeds as follows. I first review De Haan and Dahm’s criteria of personhood and their Middle Way proposal. I then examine Aquinas’s metaphysics of composition and numerical identity and develop the Mixed View on this basis. Subsequent sections address its implications for understanding death as a substantial change, the abnormality of the post-mortem state, and objections concerning dualism and species. The final section assesses the theoretical advantages of the Mixed View within Thomistic metaphysics.

2. The Middle Way: The Separated Soul as an Incomplete Person

2.1. The Criteria of Personhood

In Summa Theologiae, Aquinas examines Boethius’s classic definition of person: “a person is an individual substance of a rational nature.”5 Aquinas explicitly accepts this definition and responds to various objections. He notes: “in the aforementioned definition of a person, ‘individual substance’ is included insofar as it signifies a singular in the genus of substance; and ‘of a rational nature’ is added insofar as it signifies a singular among rational substances.”6 Aquinas maintains this definition throughout his other works as well (e.g., In III Sent, d. 5, q. 3, a 2, resp; CT. I. 210). By analyzing this definition, De Haan and Dahm distinguish three criteria of personhood: Subsistence Criterion, Rationality-of-the-Supposit Criterion, and Completeness Criterion (cf. De Haan and Dahm 2019, pp. 591–611).

The Subsistence Criterion of Personhood dictates that if a being is a person, it must be an individual that subsists per se (cf. De Haan and Dahm 2019, p. 598). Here, “an individual that subsists per se” refers to a hypostasis or a primary substance (substantia prima) (cf. ST. I, q. 29, a. 1, resp). The term “individual” further emphasizes the unique individuality of a person. Aquinas maintains that a person possesses the most specific kind of individuality. A person is “incommunicable” (incommunicabilis) in the following three senses: first, it is neither a part of any whole, nor a universal communicable to plural individuals, nor something that cannot be assumed by another person (cf. In III Sent, d. 5, q. 2, a. 1, ad. 2).

The Rationality-of-the-Supposit Criterion dictates that if a being is a person, it must be a supposit that performs rational actions by virtue of its rational nature (cf. De Haan and Dahm 2019, p. 608). This criterion involves an important distinction between the “rational nature in virtue of which one acts” and the “supposit which acts in virtue of that rational nature.” Aquinas maintains that the rational soul is the principle by which intellectual and volitional actions are performed, whereas the proper supposit of rational actions is the possessor of the rational soul. He states: “in creatures, actions belong to supposits; and that essence does not act, but is the principle of action in the supposit.”7 To illustrate this distinction, Aquinas draws an analogy between the soul’s understanding and the actions of the hands and feet. He states: “for a man sees with the eye, walks with the foot, and likewise understands through the soul.”8 For this reason, it is the supposit (the individual person) that is rewarded or punished for its actions, rather than in virtue of which the action is performed (such as the soul or bodily organs) (cf. ST. III, q. 7, a. 13). Therefore, according to Rationality-of-the-Supposit Criterion, a person must not only possess a rational nature but must also be the supposit or agent of rational actions. It should be noted that in the definition of a person, “rational” does not refer narrowly to human reasoning, but broadly to the intellect, encompassing the cognitive modes that transcend those of corporeal beings (cf. ST. I, q. 29, a. 3, ad. 4).

At first glance, the Subsistence Criterion and the Rationality-of-the-Supposit Criterion seem to exhaust Boethius’s definition of person. Aquinas explicitly points out that the human soul “is a this something and subsists per se, because it operates per se”9; furthermore, “’a this something’, properly speaking, designates an individual in the category of substance.”10 From this perspective, the separated soul appears to satisfy both criteria for personhood. However, Aquinas anticipates this point and notes: “a rational soul is called a ‘this something’ in the way that being subsistent is a ‘this something,’ even though it has the nature of a part; yet the nature of person further requires that which is a whole and a complete.”11 De Haan and Dahm summarize this as the third criterion for personhood: the Completeness Criterion—if a being is a person, it must be complete or a whole (De Haan and Dahm 2019, p. 611). As a being that subsists per se, the separated soul is complete in existence (esse), but because it lacks the body, it remains incomplete in species or essence (essentia).

Taken together, these criteria clarify Boethius’s definition. A person is a subsisting individual who is the agent of rational acts and who possesses completeness in both existence and essence.

2.2. Separated Soul as Incomplete Person

De Haan and Dahm argue that the separated soul satisfies these three criteria only incompletely.

First, with respect to the Subsistence Criterion, they appeal to Aquinas’s discussion of the soul as a “this something”. Aquinas maintains that “an individual within the category of substance is not only able to subsist through itself, but is also something complete belonging to some species or genus of substance.”12 However, the soul “does not have complete species, but the body comes to it for the completion of the species.”13 In this sense, “although the human soul subsists per se, it does not have a complete species per se.”14 For Aquinas, “the human soul is not a this something as though it were a substance having a complete species, but inasmuch as it is a part of a thing having a complete species.”15 Accordingly, De Haan and Dahm contend that while the separated soul subsists per se completely in existence, it is not a complete individual due to the lack of a complete specific nature. For this reason, they conclude that the separated soul satisfies the Subsistence Criterion only incompletely (De Haan and Dahm 2019, p. 615).

Secondly, regarding the Rationality-of-the-Supposit Criterion, De Haan and Dahm maintain that once separated, the soul is indeed the supposit of rational acts (De Haan and Dahm 2019, p. 622). In his discussion on whether the body is required for beatitude, Aquinas also points out that “after being separated from the body it has perfect being and that consequently it can have a perfect operation; although it does not have the perfect specific nature.”16 However, De Haan and Dahm contend that because the separated soul is incomplete in its specific nature, it functions as a supposit that performs rational actions through an incomplete rational nature. Thus the second criterion, too, is satisfied only in a qualified sense (De Haan and Dahm 2019, p. 622).

Third, and most explicitly, De Haan and Dahm argue that the separated soul incompletely satisfies the Completeness Criterion: “a separated soul is incompletely complete” (De Haan and Dahm 2019, p. 623). They distinguish several kinds of completeness relevant to personhood: completeness of perfect intellectual action, of subsistence, of the substantial form, of the supposit, and in species (De Haan and Dahm 2019, pp. 623–24). The separated soul satisfies the first four kinds but lacks completeness in species since it is not a whole human being. Consequently, it satisfies the Completeness Criterion only incompletely (De Haan and Dahm 2019, p. 630).

On this basis, De Haan and Dahm conclude that the separated soul is neither simply a person nor simply not a person but rather an “incomplete person” (De Haan and Dahm 2019, p. 630). The notion of incompleteness thus functions as the unifying strategy of their Middle Way: each criterion of personhood is met, yet only in an incomplete mode.

2.3. A Reflection on the Middle Way

Although De Haan and Dahm’s Middle Way successfully avoids many of the standard difficulties facing both corruptionists and survivalists, a natural concern arises regarding the coherence of the notion of an “incomplete person”: is the notion of being “incompletely complete” or “incompletely satisfying the criteria for personhood” conceptually self-contradictory? De Haan and Dahm seem to claim that “the separated soul both is and is not a person; it both satisfies and does not satisfy the criteria for personhood.”

De Haan and Dahm acknowledge the apparent tension, conceding that “the notion of an ‘incomplete person’ is an oxymoron—a contradiction in terms” (De Haan and Dahm 2019, p. 623). Their reply appeals to Aquinas’s claim that death is an unnatural (contra naturam) condition for a human being, and surviving death is extraordinarily unnatural. They think that “the notion of an incomplete person does not misrepresent death but draws attention to its unnaturalness by articulating a precise metaphysics of this unnatural incomplete being” (De Haan and Dahm 2019, p. 632).

However, appealing to the unnaturalness of death does not by itself resolve the conceptual difficulty. The fact that a state is contra naturam does not entail that its description must involve conceptual tension or contradictory predicates. Blindness, for example, is contrary to the natural functioning of sight, yet the concept of blindness is neither self-contradictory nor unnatural. The question, then, is not whether the separated soul exists in an abnormal state but whether “person” admits of partial instantiation in the relevant metaphysical sense.

Mark K. Spencer also notices this. He pointed out that “incomplete person, supposit or hoc aliquid each strike me as an alienans phrase, like dead animal, and as a self-contradictory phrase, like square circle” (Spencer 2020, p. 182). De Haan and Dahm respond that “’person’ is a putatively analyzable notion and it is always an open question of whether such notions admit of secundum quid instances” (De Haan and Dahm 2020, p. 172). They hold that an “incomplete person” is a person secundum quid, and a “person secundum quid” is not an alienans term (cf. De Haan and Dahm 2020, pp. 172–73).

The appeal to secundum quid predication likewise requires clarification. De Haan and Dahm suggest that “person” is an analyzable notion and that such notions may admit of qualified or secundum quid instances. “Person” is indeed an analyzable notion. However, one of the analysans is “substance”, which is precisely in the definition of “person”. Yet in Aquinas’s metaphysics, substantial terms do not admit of degrees in the same way accidental predicates do. Accidentals can be received by a substance “to a greater or lesser degree” (suscipere magis et minus); a substance may be more or less white. But “personhood” is not an accidental quality. It signifies a subsisting substance of a certain nature. To speak of something as “not entirely a person” risks introducing ontological vagueness. Aquinas does recognize hierarchical distinctions among persons: divine, angelic, and human. But this hierarchy concerns an ordinal difference in the perfection of rational substance kinds, not a gradual difference in the degree of personhood itself. Personhood, as a substantial property, inherits Aquinas’s metaphysical principle that substantial predicates admit of no magis et minu—just as a cow cannot be more or less a cow (a substantial kind), a rational substance cannot be more or less a person. Although “person” is a notion admit of secundum quid instance, the instances here do not seem to include an “incomplete person”. Instead, they are like a “white person” or a “material person”, etc. For this reason, the notion of “incomplete person” seems to be problematic.

A further consideration strengthens the concern for the Middle Way. Although De Haan and Dahm’s criteria of personhood are formulated universally, their discussion repeatedly emphasizes that “the separated soul is incomplete in species” (De Haan and Dahm 2019, p. 630), that is, incomplete as a human being. This suggests that the underlying issue may not be whether the separated soul is a person simpliciter, but whether it is a human person. If so, the debate shifts from the general metaphysics of personhood to the specific question of human personal identity. De Haan and Dahm rightly show that the separated state lacks the completeness of human personhood—a conclusion rooted in the metaphysical reality of human nature as a composite of soul and body. This paper extends their insight by asking whether the post-mortem prime substance retains personhood. This question is a deeper engagement with them. The aim of the present paper is not to reject the Middle Way but to retain its clarified criteria of personhood while re-examining the metaphysical framework within which they operate. The difficulty surrounding “incomplete personhood” indicates not merely a semantic tension but a need for a more systematic integration of composition, substantial identity, and species membership. The following sections pursue this task.

3. The Mixed View

As previously indicated, this section will propose a Mixed View. Its core tenets are that after death an individual, such as Socrates, (1) survives; (2) remains a person; (3) is no longer a human person; and (4) his soul is not a person. To argue for (1) and (2), we must sequentially introduce Aquinas’s views on composition and the Numerical Identity Of Substances.

3.1. Aquinas on Part, Whole and Composition

For Aquinas, composition can be understood as the relationship between parts and the whole: the whole is composed of its parts, and the parts compose the whole. Aquinas distinguishes between various types of parts and wholes, as shown in Figure 1 below.

For the scope of this discussion, we are concerned only with the substance as an integral whole and with matter and form as its essential parts. Contemporary Thomists also refer to such parts as “metaphysical parts”, distinguishing them from “physical parts” such as hands or feet (cf. Stump 2003, pp. 35–53; Brown 2005, pp. 53–103; Brower 2014, pp. 130–33). Correspondingly, the relationship between metaphysical parts and the substance can be termed “metaphysical composition”, distinguishing it from other kinds of part-whole relationships.17 For instance, the relationships Aquinas describes between “a universal part” (pars universalis) and a universal whole, or between “a potential part” (pars potentialis) and a potential whole (cf. In III Sent, d. 33, q. 3, a. 1, qa. 1, co), are not metaphysical composition. In the following text, unless otherwise specified, “composition” refers exclusively to “metaphysical composition”.18

There are two rules regarding composition that are closely related to the discussion in this paper. The first is that no whole is identical to its part(s). Aquinas states: “the composite itself must not be identical with its components, as a syllable is not its letters.”19 Therefore, in the sense of contemporary mereology, we can say that Aquinas (partly) opposes “Composition as Identity” (CAI). A classic example of CAI is that a six-pack of beer, as a whole, is composed of six bottles of beer; a six-pack of beer just is the six bottles of beer (cf. Varzi 2016). For Aquinas, however, a six-pack of beer is not composed of six bottles of beer, but merely an aggregation of them. Composition, by contrast, is a more “metaphysically loaded” relationship. In contemporary mereology, this rule is known as “Composition as Non-Identity”, and it does not lack defenders (cf. Koslicki 2008, pp. 45–68; Cameron 2014).

The second rule is what may be called the Single-Part-Composition: under certain conditions, a substance can be composed of a single proper part.20 In mereological terms, this means that composition in Aquinas does not require Weak Supplementation (Oderberg 2012). Single-Part-Composition is not an isolated Thomistic oddity but has been recognized both by Thomists (cf. Stump 2006; Brown 2005, pp. 77–78) and contemporary metaphysicians (e.g., Oderberg 2005). Its most systematic recent deployment is found in Brower (2014), who applies it to post-mortem survival and to Christological questions concerning the triduum (Brower 2014, pp. 291–301). The present discussion adopts this rule in a similar way. In the case at hand, the separated soul, as a substantial form, composes a substance on its own. This is not an isolated Thomistic peculiarity. It resonates with broader hylomorphism (both Thomistic and non-Thomistic) that allows form to play a robust role (e.g., Lowe 1998). At the same time, it is not without analogues in contemporary debate. Achille Varzi (2016) shows a range of disagreement with Weak Supplementation and, interestingly, includes Aquinas’s view of the separated soul as a significant case. Single-Part-Composition can also be extended beyond the human case to incorporeal creatures more generally. An angel, as a created immaterial substance, may be described as composed of its sole substantial form, lacking any material component yet still remaining metaphysically composite. Indeed, this framework may even help to illuminate a traditional Thomistic contrast between angels and God: whereas an angel, though immaterial, can be said to possess one proper part, God has no proper parts at all and is wholly devoid of form and composition, which explains absolute divine simplicity metaphysically.

3.2. Aquinas on the Criterion of the Numerical Identity of Substances

For Aquinas, the numerical identity or being numerically the same of a substance is guaranteed by the numerical identity of its substantial form: for substances S₁ and S₂, if S₁ and S₂ have a numerically identical substantial form, S₁ and S₂ are numerical identical. In other words, the numerical identity of the substantial form is the “Criterion of the Numerical Identity of Substances”. As such, this criterion is both synchronic and diachronic. The “numerical identity” of a substance is different from specific or generic identity. It refers to the substance being “one in number” (unum numero) or its “oneness” (unitas). Aquinas distinguishes between two kinds of “one” and “oneness”: one is “’discrete quantity’ (discreta quantitas) caused by the division of matter or a continuum”21, that is, “oneness in quantity”, which belongs only to material substances; the other “one” can be used interchangeably with “being”, which is a transcendental, not limited to any category and can be possessed by all entities (cf. In I Sent, d. 24, q. 1, a, 1 ad. 1). This kind of oneness is from the substantial form, as Aquinas states: “a thing has being and oneness from the same thing; for one and being are consequent upon one another. Now everything has being through its form. Therefore, the oneness of a thing is consequent upon the oneness of the form.”22 The “form” mentioned in the quotation is clearly the “substantial form”. The substantial form makes a substance exist simpliciter or have esse substantiale and makes it simpliciter one (cf. DPN, c. 1).

3.3. Core Claims of the Mixed View

Next, taking Socrates as an example, based on “Composition as Non-Identity”, “Single-Part-Composition”, and the “Substantial-Form-Based Criterion of the Numerical Identity of Substances”, we can derive the following propositions.

Let:

• S₁ = Socrates before death.
• SF₁ = the substantial form or soul of S₁.
• SF₂ = the separated soul of Socrates after death.
• S₂ = the substance composed solely of SF₂.

We affirm:

(i)

SF₁ is a proper part of S₁.

(ii)

S₁ is a person.

(iii)

SF₁ is numerically identical to SF₂.

(iv)

SF₂ is the sole proper part of S₂.

(v)

SF₂ is not numerically identical to S₂.

(vi)

S₁ is numerically identical to S₂.

(i) and (ii) are uncontroversial: Socrates is a human person; surely, he is a person, and his soul, as a substantial form, is a part or a component of himself. It should be emphasized that SF₂ (the rational soul), as a metaphysical part of S₁, is not a neutral or undifferentiated constituent. By its very nature, SF₂ is the soul of hoc caro, that is, it bears an essential, intrinsic referentiality to body—not to any indeterminate body or matter, but to a certain body that it actualizes. (iii) is entailed by the notion of a “separated soul”: death is the separation of Socrates’s soul from his body, not its annihilation and the generation of a new soul. (iv) is an application of “Single-Part-Composition,” while (v) applies “Composition as Non-Identity.” Finally, (iii) and (vi) are derived from the “Criterion of the Numerical Identity of Substances.” The present argument proceeds by showing that S₂ independently satisfies the criteria of personhood articulated by De Haan and Dahm.

First, S₂ completely satisfies the Subsistence Criterion of Personhood. De Haan and Dahm argue that SF₂ (the separated soul) only satisfies this criterion incomplete because, as a part of a human being, it is incomplete in its specific nature. However, according to (v), S₂ is a substance and is not a part of any other substance. A substance is an individual that subsists per se with complete being and essence. The nature of this essence is a separate question to be discussed later.

Second, S₂ completely satisfies the Rationality-of-the-Supposit Criterion. Since S₂ is composed solely of SF₂, which is a rational soul, S₂ possesses a rational nature and performs rational actions accordingly: S₂ understands and wills through SF₂. De Haan and Dahm might argue that S₂, like SF₂, only incompletely satisfies this criterion because it acts through an incomplete nature. This, however, presupposes that S₂ (or SF₂) is an incomplete human person. I make no such presupposition; as stated above, as a substance, the specific nature of S₂ is complete.

Finally, S₂ completely satisfies the Completeness Criterion. S₂ not only possesses the requirements for “completeness of perfect intellectual action”, “completeness of subsistence or existence”, “completeness of the substantial form”, “completeness of the supposit”, as De Haan and Dahm think SF₂ also possesses, but also possesses completeness in species as previously argued.

Therefore, S₂ is a complete person, and (vii) is true. Notably, if the conclusion of De Haan and Dahm is interpreted as “the separated soul is not a complete human person”, then (vii) does not actually conflict with their view. Furthermore, through the preceding discussion, we can derive (viii): S₂ is not a human person. A human person is essentially embodied. Since S₂ lacks any material principle, it cannot instantiate human nature, even though it remains numerically identical to the pre-mortem individual.

We can also derive (ix): SF₂ is not a person. If (vii) is true and S₂ is a person, then according to the Rationality-of-the-Supposit Criterion, S₂ is the supposit of rational actions. If SF₂ were also a person, the same rational action would have multiple supposita or “possessors”. This not only violates Aquinas’s principle that action belongs to the supposit and that one act has one agent simpliciter but also the Priority Principle (cf. Skrzypek 2017). Moreover, according to De Haan and Dahm’s distinction between the “rational nature by which one acts” and the “supposit which acts by its rational nature”, SF2 is more properly identified as a rational nature rather than a supposit.

(vi), (vii), (viii), and (ix) correspond, respectively, to the four core claims of the Mixed View introduced earlier: that an individual person, such as Socrates, after death and before resurrection, (1) survives and (2) remains a person; yet, at the same time, (3) he is not a human person, and (4) his soul is not a person. The Mixed View is not an ad hoc synthesis. It follows from jointly applying principles already accepted within Thomistic metaphysics. Once Single-Part-Composition, Composition as Non-Identity, and the Substantial-Form-Based Criterion of Numerical Identity are consistently integrated with the criteria of personhood, the four core claims follow with systematic necessity. In the following section, I will further demonstrate the plausibility and acceptability of the Mixed View by examining and resolving three potential objections.

4. Potential Objections and Responses

4.1. What Kind of Person S₂ Is?

The first concern regarding the Mixed View is this: if S₂ is a person (vii) but not a human person (viii), then what kind of person is it? More precisely, in what specific nature, if any, is S₂ complete?

I propose that S₂ is specifically a “quasi-angel”. Aquinas explicitly considers “whether the soul is of the same species as an angel” in the Summa Theologiae (I, q. 75, a. 7), rejecting the Origenist claim that human souls and angels are specifically the same. Notably, the third objection there notes that “it seems that the soul does not differ from an angel except in its union with a body.”23 Once separated, the difference indeed appears attenuated. Aquinas’s response provides two decisive principles: first, “The body is not of the essence of the soul; but the soul by the nature of its essence is unitable (unibilis) to the body;” second, “properly speaking, not the soul alone, but the composite, is in the species.”24 These two claims allow us to clarify why S₂ is not an angel, yet also not a human being, but a “quasi-angel”.

With respect to mode of being, composition, and action, S₂ resembles an angel. Both subsist per se; both perform rational actions without bodily organs; both lack matter as an actual component. In this sense, S₂ is closer to angelic substances than to embodied human beings. Yet Aquinas insists that the difference between soul and angel does not lie in actual embodiment, but in unitability. This unitability is a potentiality, a disposition, or an inclination. It is precisely due to this difference in disposition that Aquinas maintains that while an angel may assume a body under specific circumstances, it does not do so naturally or by an inherent inclination of its nature (cf. ST. I, q. 51, aa. 1-2). Similarly, although S₂ actually lacks a body or matter as a part, it remains naturally and essentially inclined toward embodiment due to the disposition of the rational soul. Thus, the difference between S₂ and an angel is essential.

Aquinas’s claim that “properly speaking, not the soul alone, but the composite, is in the species” is crucial. This perfectly aligns with the distinction emphasized in this paper between the “substantial form as a part” and the “substance composed solely of that substantial form”. Angels are sometimes called “subsistent forms”, but strictly speaking, it is the angelic substance, not a form considered as part, that belongs to a species.25 Likewise, in a strict sense, it is not the separated form of S₂ that is a quasi-angel; rather, S₂ itself is a quasi-angel.

Aquinas maintains that “things agree in species but differ in number, agree in form, but are distinguished materially.”26 Since angels are not composed of matter and form, it is impossible for two angels to belong to the same species (cf. ST. I, q. 50, a. 4, resp.). In other words, a crucial difference between the term “angel” and “human” is that the latter signifies species infima, whereas the former does not.27 However, the term “quasi-angel” is not intended to introduce a new natural species in the strict Thomistic sense. Rather, it functions as a metaphysical descriptor, indicating a mode of subsistence and operation that resembles that of angelic substances while remaining essentially distinct from them. The term “quasi-angel”, therefore, should be understood as designating a non-human rational kind characterized by immaterial subsistence and intellectual operation, yet essentially marked by an intrinsic disposition toward embodiment. This designation carries no implication of ontological superiority or an intermediate rank between human beings and angels. On the contrary, in line with Aquinas’s doctrine, this “quasi-angelic” mode of existence is an unnatural, ontologically deficient state for the rational soul—one that lacks the integral perfection of the embodied human person, and is far inferior to the perfected unity of the resurrected human person. The “quasi-” prefix denotes nothing more than a superficial similarity in operational and subsistential mode (immaterial intellective activity), not a kinship in ontological nature, perfection, or hierarchical rank.

Regardless, as a quasi-angel, S₂ remains distinct from an angel in its principle of individuality. Aquinas argues that since angels lack matter, they and their forms are individuated per se (cf. DEE, c. 4). The individuation of S₂ is more complex. One view holds that an individual human person (S₁) and her rational soul (SF₁) are individuated by matter, thereby acquiring individuality; once this individuality is conferred, it is retained. Thus, even when the soul (SF₂) is separated from the body, it preserves its individuality (cf. Pasnau and Shields 2004, p. 57). This “retained individuality” ensures that the disposition of the soul (SF₂) and the substance it composes (S₂) are individuated. That is to say, Socrates’s separated soul possesses not just a general “unitability” with a body, but an individuated “unitability with Socrates’s specific body.” Likewise, S₂ retains this specific “disposition to regain Socrates’s body.” This aligns perfectly with Aquinas’s doctrine that resurrection consists of the soul regaining the numerically same body (cf. CT. I, c. 154).

Here the divergence from Brower becomes precise. Brower does not claim that S₂ is a human person in the ordinary, fully actual sense. Rather, he broadens the term “human” to include a substance that retains a natural disposition to be human in virtue of the soul’s persistence. On this basis, Socrates survives death “as a human person” in a broad sense (Brower 2014, pp. 295–96). The Mixed View agrees on nearly all structural points: numerical identity, persistence of the soul as the sole proper part, and retention of an intrinsic ordination toward embodiment. The disagreement concerns species attribution.

Brower’s broadened usage allows the surviving Socrates to be called “human” in virtue of a retained disposition. However, a retained disposition toward humanity does not suffice for being human. The menstrual blood (in Aquinas’s biology), for instance, is dispositionally to be a human being yet is arguably not a human person. At the same time, dispositions are too weak to capture the metaphysically significant difference between S₁ and S₂: arguably, S₁ possessed the same disposition toward future embodiment without ceasing to be actually human. Dispositional criteria, therefore, fail to mark the metaphysical difference introduced by death.

For this reason, S₂ is described as quasi-angelic: continuous in numerical identity and substantial form, discontinuous in species. The dispute with Brower concerns not survival, nor whether the soul alone is a person (both views deny this), but how sharply the metaphysical difference introduced by death should be drawn.

Table 1. A Comparison of Survivalism, Corruptionism, the Middle Way, and the Mixed View.

Standpoint	What Survives After Socrates’s Death?	Is It a Person?	Is It a Human Person?
Corruptionism	Socrates’s soul.	No.	No.
Survivalism (standard)	Socrates’s soul.	Yes.	Yes.
The Middle Way	Socrates’s soul.	Not completely is, nor completely not.	Not completely is, nor completely not.
Brower’s Survivalism	Socrates.	Yes.	Yes, in a broader sense.
The Mixed View	Socrates.	Yes.	No.

below can clearly illustrate the differences between the Mixed View and Brower’s Survivalism, as well as the Middle Way and the Corruptionism and Survivalism (standard). We can observe that, compared to other Standpoints, the Mixed View and Brower’s viewpoint are extremely close.

4.2. How to Characterize Death as a Substantial Change?

Aquinas treats death as a substantial change, involving substantial generation and corruption (cf. DPN. c. 1). A primary criticism from Corruptionists against Survivalists is that the latter, by asserting the continuity of the person, fails to account for death as a substantial change (cf. Toner 2010). Since the Mixed View maintains both survival and personal status, it appears vulnerable to the same charge.

However, Aquinas distinguishes between two types of death: the death of the human body and spiritual death (cf. CT. I, c. 239). Our scope is the former. One straightforward response is that while Socrates survives bodily death without undergoing personal generation or destruction, new substances are indeed generated in the process—namely, the “corpse” as a complete substance, or the various body parts (hands, feet, or the elements) transitioning from potential substances to actual ones (cf. Brower 2014, pp. 291–301). Thus, we must distinguish between the “death of Socrates” and the “death of Socrates’s body”. The former does not occur. In this sense, Socrates is immortal, while the latter certainly occurs, accompanied by the generation of new substance(s).

Yet, this response might be criticized for failing to capture the abhorrence or unnaturalness of death. My further response is that death, as a substantial change for Socrates, involves not only the generation of a corpse but also the destruction of a substance of an old species and the generation of a substance of a new species. As discussed, S₁ is specifically a human, while S₂ is a quasi-angel. In other words, death is a substantial change for Socrates as a human, though Socrates as a substance or supposit survives. While S1 is numerically identical to S₂, they exhibit a specific difference. This allows us to explain the “abhorrence” and “unnaturalness” of death: S₁, a human species, possesses a natural disposition to preserve that specific nature and thus abhors death; S₂, as a quasi-angel, retains the disposition to regain a body but currently lacks one and cannot naturally recover it. This state is, therefore, ontologically unnatural (cf. CT I, c. 154). This explanation of “unnaturalness” appears more robust than that of De Haan and Dahm. While they rely on strained notions like “incompletely complete” to characterize death, my proposal is notionally and metaphysically natural.

At this point, an important clarification is required. I do not claim that Aquinas generally allows numerical identity to come apart from specific identity. Ordinarily, the substantial form that grounds identity also grounds species-membership. Within Aquinas’s metaphysics, the numerical identity of a substance is ordinarily accompanied by the persistence of the same specific nature. However, the Mixed View concerns an exceptional, contra naturam condition in which the form persists while its natural completion is interrupted. In such a condition, the substantial form’s role as the principle of a determinate species is suspended or altered due to the loss of the matter. Accordingly, the claim defended here is not that numerical identity in general fails to entail specific identity, but rather that under extraordinary, non-natural conditions, numerical identity may persist without the persistence of species. The Mixed View, therefore, extends Aquinas’s metaphysics only in this abnormal domain, rather than revising his general metaphysics.

4.3. Why Single-Part-Composition Is Exceptional?

A serious worry is that Single-Part-Composition reintroduces dualism. According to Single-Part-Composition, if the soul can compose a substance solely, why does it not always do so? Why does the soul not compose one substance solely while simultaneously composing another substance with the body? Why is the embodied human not simply one substance composed of soul and body in addition to a second substance composed by the soul solely? Furthermore, how may we characterize the non-necessity of Single-Part-Composition?

Aquinas’s arguments against Averroistic Monopsychism and Platonic dualism block these consequences. Monopsychism posits that the separate intellect is claimed to be functionally linked to individuals through their phantasms, precisely so it can remain one and the same for all humans (cf. De unitate intel. c. 1). This view is strikingly similar to the worry that a soul might compose a substance while simultaneously composing another one with body. Aquinas counters this by emphasizing the individuality of the “act of understanding” and the “act of being” (actus essendi). Since understanding is properly to the individual and performed through its form, “but the same numerical form cannot belong to that which are not numerically the same, as everything has being by its form.”28 In other words, because the act of being conferred by a substantial form cannot be shared by plural substances or is incommunicable in Aquinas’s terms, a soul cannot be a part of plural substances simultaneously.29 Thus, a soul cannot compose a substance solely and compose another substance together with body simultaneously. In addition, according to the Criterion of the Numerical Identity of Substances, whether the soul composes a substance solely or together with body, they are numerically one substance.

Platonic dualism posits that the soul is merely the “motor” of the body, and that the body, as a substance, possesses its own distinct substantial form (cf. ST. I, q. 76, a. 4, resp). This view aligns with the concern that the soul might compose one substance solely while the body exists as another. Aquinas, throughout his career, adamantly opposed the “plurality of substantial forms”, maintaining that a single substance can possess only one substantial form (cf. CT. I, c. 154). As the soul is the substantial form of the human being, it is necessarily unique. He writes: “one thing is of one substantial being. But a substantial form gives substantial being. Therefore, one thing is merely of one substantial form. But the soul is the substantial form of human. Therefore, it is impossible for there to be in human another substantial form besides the intellectual soul.”30 Since it is impossible for a human to possess any substantial form other than the rational soul, it follows that when the soul is united with the body, the soul does not compose a substance sole while the body possesses a separate substantial form as another substance.

Why, then, does the soul not always compose a substance solely, but instead unites with a body or matter in the majority of cases? My response proceeds in three steps: first, by establishing the possibility of union; second, by establishing the possibility of separation (or the non-necessity of union); and third, by explaining the naturalness of union. Together, these explain why the soul can compose a substance solely and together with a body, and why it predominantly does the latter.

As previously mentioned, the human soul possesses an inherent unitability, which accounts for the possibility that it composes a substance together with body. Yet, Aquinas maintains that this unitability “does not prevent the intellect being separated from the body.”31 Although the soul is the form of the body, its rational actions do not essentially depend on bodily organs; it retains actions independent of the body and is thus a subsistent being per se (cf. ST. I, q. 75, a. 2, resp). Consequently, Aquinas argues that human souls as forms “are not altogether material and wholly merged in matter.”32 This provides the metaphysical possibility of separation.

However, for Aquinas, separation is an unnatural state for the rational soul, termed “beyond the soul’s nature” (ST. I, q. 89, a. 1, resp). Conversely, union with the body is a natural disposition, as Aquinas states, “not such that being united to the body is accidental to it, but rather it is united to the body by the ratio of its nature.”33 In his view, “it is better for the soul to be united to the body.”34 For this reason, in the state of Original Justice, the body was perfectly subject to the soul, and there was no separation, death, or disease (CT. I, c. 83). The necessity of death and the separation of the soul are consequences of Original Sin (CT. I, c. 90). The possibility and naturalness of union, alongside the possibility and (post-lapsarian) necessity of separation jointly explain why the soul composes a substance solely only under the exceptional condition of death. Thus, the “quasi-angelic” state of S₂ is an exception and an unnatural state rather than the norm. This further underscores the inherent abhorrence of death and the absolute necessity of the Resurrection.

The Mixed View proposed here should not be read as a merely exegetical claim about what Aquinas explicitly states. Rather, it is a systematic clarification, application and reconstruction of Aquinas’ numerous viewpoints. The view preserves core Thomistic commitments: hylomorphism, the unity and incommunicability of substantial form, the natural disposition of the soul to the body, and the characterization of death as praeter naturam, while extending their explanatory reach to cases Aquinas did not explicitly theorize in detail. In doing so, the Mixed View shows that Thomistic metaphysics contains latent resources for distinguishing between numerical identity and specific identity. The resulting account therefore occupies a middle position not only between corruptionists and survivalists, but also between strict textual minimalism and unconstrained speculative metaphysics: it is an extension, not a revision, of the Thomistic framework.

5. Theoretical Advantages and Significance of the Mixed View

As established, this theory does not deny the intuition held by De Haan and Dahm that “the separated soul is not a complete human person”. Rather, by introducing “Single-Part-Composition”, it demonstrates the rationality of Socrates’s persistence as a person after death. Consequently, this approach not only preserves the positive fruits of the Middle Way but also surpasses it in several key aspects. More fundamentally, the view clarifies the metaphysical structure presupposed by Aquinas’s account of substance, personhood, and death, thereby reshaping the conceptual landscape of the debate.

First, this theory avoids inherently contradictory or strained notions such as being “incompletely complete” or “incompletely satisfying criteria of personhood” as the Middle Way does. The four core claims of this theory are conceptually natural and contain no contradictory expressions, thereby circumventing the ontological vagueness implied by the term “incomplete person”. Nevertheless, this theory can still emphasize the “unnaturalness of death” (a key concern of the Middle Way) without relying on such strained notions; as we shall see in the next section, (viii) inherently accounts for this unnaturalness and explains how death is understood as a “substantial change”.

Second, by upholding (v) (the deceased Socrates is not identical to his soul), we can offer a more robust interpretation of specific texts. For instance, Aquinas’s famous dictum, “anima mea non est ego” (My soul is not me) (Super I Cor. c. 15, I. 2), is effectively a statement of (v). In contrast, the Middle Way must interpret this as “my soul is neither the ‘complete me’ nor is it ‘completely not me’“, an interpretation that appears significantly more tenuous.

Third, the Mixed View yields a more precise account of death as a substantial change. Corruptionism preserves substantial change at the cost of personal annihilation; standard survivalism preserves the person but risks reducing death to a merely accidental alteration. The present account avoids this dilemma by locating substantial change at the level of species. Death involves the loss of the human mode of substantial actuality and the emergence of a quasi-angelic mode, even though the same substance and person persist. In this way, death remains metaphysically profound without entailing the destruction of the person.

Fourth, the view remains faithful to Aquinas’s anti-dualist commitments. By maintaining that the soul is not identical with the surviving substance, it upholds the principle that the human person is not merely a soul. At the same time, Single-Part-Composition allows for post-mortem substance without positing two substances during embodied life. The theory, therefore, explains survival without reintroducing a Platonic dualism.

Fifth, the Mixed View possesses explanatory power across doctrinal contexts central to Aquinas’s thought. It clarifies why the intermediate state is both real and metaphysically abnormal, grounding the necessity of resurrection. It also coheres naturally with the view that it is the persons themselves, rather than merely their souls, who are the supposits of post-mortem cognition, beatitude, and intercessory significance. In these respects, the Mixed View integrates metaphysical analysis with the theological structure within which Aquinas’s anthropology operates.

What ultimately distinguishes the Mixed View defended in this paper is not the introduction of new metaphysical principles, but the systematic coordination of several Thomistic commitments that have rarely been brought together within a single explanatory framework. Single-Part-Composition, Composition as Non-Identity, the Substantial-Form-Based Criterion of Numerical Identity of substance, and the personhood criteria articulated by De Haan and Dahm are all individually familiar. What has not been fully appreciated is how strongly they constrain one another once jointly applied to the post-mortem condition. When these principles are allowed to operate without restriction, they converge on a determinate ontological outcome: the separated soul cannot be the person; yet neither can the person cease to exist; and the post-mortem supposit must therefore be a substance composed solely of the rational soul. The Mixed View is thus less a speculative proposal than the result of taking Thomistic metaphysical structure with full consistency. In this respect, the long-standing impasse between Corruptionists, Survivalists, and defenders of the Middle Way reflects not an absence of resources in Aquinas but an incomplete integration of them. Seen in this light, the post-mortem state no longer appears as a marginal anomaly, but as a test case that reveals the internal coherence of Aquinas’s metaphysics.