1. Introduction
For years, interpreters of Aquinas have debated his view on the status of the human being (homo) or person (persona) immediately after death and before the resurrection.Footnote 1 The debate concerns whether, for Aquinas, the survival of the human soul in separation from the body is sufficient for the survival of the human being or person – Socrates, Plato, and so on – as well. Survivalists hold that the separated soul’s survival is indeed sufficient for the human being’s continued existence; corruptionists deny this, insisting that the body is also necessary for a human being to exist, absolutely speaking. The early years of the debate tended to focus on specific things that Aquinas says about the separated soul and human beings or persons in the interim period between death and resurrection. More recently, however, the debate has begun to turn to broader metaphysical considerations. This turn has revealed that survivalists and corruptionists in fact disagree about how to understand some of Aquinas’s most basic metaphysical principles.Footnote 2 In this paper, I want to focus on their disagreement about essences.
Most survivalists and corruptionists agree that Aquinas includes matter in the essence of human beings, since he defines human beings as rational animals, i.e., rational, sensing, living, material substances. But then how can a human being survive the loss of its body at death? Many survivalists have answered this question by saying that a thing’s essence and its parts are not strictly necessary for the thing’s existence; rather, a thing’s essence only represents what the thing is under natural, normal, or typical circumstances.Footnote 3 As a rational animal, a human being naturally, normally, and typically has a body, but it can exist outside of its natural, normal, and typical state, as it does immediately after death up until the resurrection.Footnote 4 I believe that this view of essences as merely normative rather than strictly necessary for a thing’s existence is not Aquinas’s own. For him, a thing’s essence, which its definition signifies, is strictly necessary for the thing’s existence; a thing cannot exist without all the parts of its essence. One place where this view of essences comes out is in Aquinas’s treatments of the logical limits of God’s absolute power or omnipotence.
For Aquinas, the limits of a thing’s power are a function of the limits of its essence. Since God’s essence is limitless existence itself, God’s absolute power extends to making anything exist that can exist. Thus, only things that involve or imply a contradiction fall outside the scope of God’s power, since such things cannot possibly exist, and thus cannot be made to exist, not even by God. Now, for Aquinas, a contradiction results from the opposition between terms: if terms signify things that are mutually incompatible, then their combination in a definition or proposition is self-contradictory, and what they signify is absolutely impossible. But, for Aquinas, the terms combined in a thing’s definition signify its essence or nature. Hence, for Aquinas, not even God can make things to be contrary to their own essences, since doing so would imply a contradiction, and is thus impossible. That is why, for example, Aquinas says that God cannot make a horse rational,Footnote 5 or a human being non-rational,Footnote 6 since he thinks that a horse is non-rational and a human being is rational by definition.
Yet if essences were merely normative for the existence of things, then this way of explaining the limits of God’s power would be inappropriate. Instead, Aquinas should say that God can make things to be contrary to their own essences. God can make a horse rational, for example, or a human being non-rational; that is not their natural or normal state, of course, but things can exist outside their natural or normal state. Yet Aquinas does not say that. Instead, he consistently appeals to the natures of things to explain why not even God can make them to be other than they are by definition. And that is because he thinks of a thing’s nature or essence, which its definition signifies, as strictly necessary for the thing’s existence. This includes the material parts of a human being’s essence. Thus, Aquinas says: ‘supposing that God intends to make a human being, it is necessary and required that he grant it a rational soul and an organized body, without which a human being cannot exist’.Footnote 7
Thus, with this paper, I would like to bolster the case for corruptionism, at least as an interpretation of Aquinas, by adding to the evidence that Aquinas held a view of essences and their parts as strictly necessary for the existence of things, rather than merely normative, as many survivalists hold. In the next section, I begin by presenting a summary of Aquinas’s account of essences and definitions, highlighting his regular comparison of them to numbers, which cannot survive the loss of any parts. In the following section, I consider the logical limits that Aquinas places on divine action in his main treatments of God’s absolute power or omnipotence. In the last section, I examine a number of specific questions about miracles that test those logical limits, in response to which Aquinas appeals to the essences of things in order to explain why God cannot make things to be other than they are by definition. Aquinas’s use of the essential definitions of things to limit even God’s absolute power to perform miracles, on pain of logical contradiction, shows that he thinks of the essences of things as strictly necessary, and not merely normative, for their existence. Yet if a thing’s essence is strictly necessary for its existence, and if matter is part of a human being’s essence, then a human being must, absolutely speaking, cease to exist with the loss of its body at death, and only begin to exist again at the resurrection. Thus, corruptionism rather than survivalism is more in line with Aquinas’s own view of natures or essences, one of his most basic metaphysical principles.
2. Essential definitions
The first chapter of Aquinas’s De ente et essentia presents a brief summary of his understanding of essences and their definitions.Footnote 8 He says that the term ‘essence’ (essentia) derives from the term ‘an existent’ (ens), the present active participle of the verb ‘to be’ (esse), in the sense in which that term posits something in reality and is divided by the ten categories of substance and accidents. Thus, ‘essence’ applies to all the natures by which different existents are placed in their genera and species. Since the definition indicating ‘what a thing is’ (quid est res) signifies its essence in this sense, the term ‘quiddity’ (quidditas) is sometimes substituted for the term ‘essence’, Aquinas says. Aristotle often called this ‘what a thing was to be’, he then notes, explaining the phrase as meaning what makes a thing to be what it is. It is also called a thing’s form,Footnote 9 in the sense of the determination of each thing, and it is called a thing’s nature, in the sense in which anything that can be grasped by the intellect is called a nature, since a thing is only intelligible through its definition and essence, Aquinas says. He adds that the term ‘nature’ refers to a thing’s essence insofar as it is ordered to its proper activity, while the term ‘essence’ is used because an existent (ens) has existence (esse) in and through its essence (essentia).
In the second chapter of the De ente, Aquinas then turns to the essences of natural substances composed of matter and substantial form, as a human being is composed of a body and rational soul. He argues that the essences of such things must include both their substantial form and matter. For ‘essence is what is signified by a thing’s definition, and the definition of natural substances includes not only form, but also matter’.Footnote 10 Such definitions do not make reference to matter as something outside the thing’s essence, as an accident’s definition makes reference to its subject, which is outside its own genus. Nor does a composite thing’s essence signify the relationship between its matter and form, or something added to them. Rather, ‘in the case of composite substances, the term essence signifies that which is composed of matter and form’.Footnote 11 As Aquinas explains:
This accords with reason, since the existence of a composite substance is not [the existence] of its form alone nor of its matter alone, but of the composite [of both]. For an essence is that according to which a thing is said to exist. Hence, the essence, by which a thing is called an existent, must not be only the form alone, nor the matter alone, but both…Footnote 12
Aquinas goes on to discuss the difference between the essence of a species and that of an individual, such as the species human being and the individual Socrates. He says that the difference between them lies only in what is designated and undesignated, that is, between what is particular and can thus be pointed out and what is general and thus cannot be. The definition of a human being contains undesignated matter, such as flesh and bone, he says, but it does not contain designated matter, such as this flesh and this bone, although Aquinas says that such designated matter would be in the definition of Socrates, if he had a definition.Footnote 13
Thus, Aquinas thinks of a thing’s essence as what the thing is, which is signified by its definition. Indeed, he often identifies a thing’s essence as what its definition signifiesFootnote 14 and identifies a thing’s definition as the phrase signifying what it is.Footnote 15 He thinks that a thing exists in and through its essence, and can only be understood through its essence and definition.Footnote 16 And in the case of composite substances such as human beings, he thinks that their essence includes both form and matter. Hence, in his commentary on Boethius’s De Trinitate, Aquinas cites human beings, whose definition he says must include flesh and bone, as an example of the kinds of things studied by physics, which he says cannot exist or be understood except in matter.Footnote 17 This is how he distinguishes the things studied by physics from the things studied by mathematics, which Aquinas says can be understood without matter although they cannot exist without matter, and from the things studied by metaphysics, which he says can both be understood and can exist without matter. Human beings cannot exist or even be understood without matter because they are natural substances whose essence and definition includes both form and matter, and a thing can only exist and be understood in and through its essence and definition.
Aquinas’s view of essences and definitions comes largely from Aristotle. In his commentary on Aristotle’s Posterior Analytics, Aquinas discusses the requirements that a thing’s definition must meet in order to signify its essence in the sense of what it is.Footnote 18 One of these requirements is that the definition must only contain terms predicated universally and always of the thing being defined.Footnote 19 For example, the definition of a human being must be true of all human beings and at all times. Something that is only true of some human beings but not others, or only true of human beings at some times but not others, cannot be what it is to be a human being. Presumably this is why Aquinas assumes that, for example, being white, and a musician, and seated, are per accidens predications of a human being; they do not tell you what a human being is per se, even if they are true of a human being,Footnote 20 since they are obviously not true of all human beings at all times. The requirement that the terms in a thing’s definition must be true of it at all times already suggests that a thing’s essence and its parts are necessary for its existence.
Another requirement for a thing’s definition is that it must contain the whole thing, and nothing but the thing, being defined. As Aquinas says in his commentary on Aristotle’s Peri Hermeneias:
A definition is called a boundary, since it includes the thing totally, namely in such a way that nothing of the thing is outside the definition, i.e., [there is nothing of the thing] to which the definition does not apply, nor is something else inside the definition, i.e., [there is nothing else] to which the definition applies.Footnote 21
Because a thing’s definition must be wholly commensurate with the thing, so that nothing within its essence falls outside the scope of its definition, and nothing outside its essence falls within the scope of its definition, a thing’s essence and its definition allow for no subtraction or addition.Footnote 22 This is one of the ways in which Aquinas, following Aristotle, says that essences and definitions are like numbers – a comparison he makes throughout his works.Footnote 23
Aristotle compares essences to numbers in book VIII of the Metaphysics. In his commentary, Aquinas notes several ways in which essences and definitions are like numbers. One way is that any addition to or subtraction from the essence signified by a thing’s definition results in a specifically different essence and definition. If anything at all is added to or subtracted from a number, the resulting number is specifically different. The same is true of a thing’s essence and definition, Aquinas says. ‘For with even the slightest thing added or subtracted, it is another definition and another specific nature’.Footnote 24 To illustrate this point, Aquinas gives the example of an animal, which he says is only defined as a sensing living substance. If ‘rational’ is added to this definition of an animal, it then signifies the nature of a human being: a rational, sensing, living substance. If ‘sensing’ is subtracted from the definition of an animal, it then signifies the nature of a plant: a living substance. Like numbers, then, a thing’s essence and its definition cannot survive the loss of any parts; any subtraction of parts makes for a change in the definition and essence.
Not only can a thing’s essence and definition not survive the loss of any parts, but the thing itself cannot survive their loss either. For a thing’s essence is that in which and through which the thing itself has existence. So, if the thing’s essence ceases to exist, and its definition no longer applies to it, the thing itself ceases to exist as well.Footnote 25 As Aquinas says in the De potentia:
An effect must depend on its cause. For this is of the nature of an effect and a cause, which comes out clearly with formal and material causes. For with any material or formal principle subtracted, the thing immediately ceases to exist, since such principles enter into the thing’s essence.Footnote 26
Thus, Aquinas considers a thing’s essential principles to be necessary for its existence. As he says in the Summa contra Gentiles: ‘Since a thing cannot exist without its essential principles, which are matter and form, whatever applies to a thing by reason of its essential principles, necessarily has an absolute necessity in all [such things]’.Footnote 27 Aquinas goes on to argue that the parts of a composite substance’s matter and form are absolutely necessary for it. His chosen example concerns the parts of a human being’s proper matter and form:
Since, then, a mixed and tempered and organized body is the proper matter of a human being, it is absolutely necessary for a human being to have in itself each of the elements and humors and principal organs. Similarly, if a human being is a rational mortal animal, and that is the nature or form of a human being, then it is necessary for it to be both an animal and rational.Footnote 28
Since matter and form are a human being’s essential principles, its ‘principles of existing’,Footnote 29 the parts of a human being’s matter and form are absolutely necessary for its existence. A human being can no more exist without a body than it can exist without being rational – the comparison Aquinas himself makes. For essences and their definitions are like numbers and do not admit the least subtraction. Indeed, not even God can make a thing exist without all the parts of its essence.
3. Divine omnipotence
It is important to consider the relationship of essences to divine omnipotence because one might wonder whether Aquinas is only speaking of what is naturally possible, that is, possible by the power of natural agents, when he says that a thing cannot exist without the parts of its essence, especially given the Aristotelian background to Aquinas’s view of essences and definitions. After all, in his commentaries on Aristotle, Aquinas says that certain things are impossible that he thinks are in fact possible for God. For example, in both his Physics and Metaphysics commentaries, Aquinas says that two bodies cannot be in the same place.Footnote 30 And yet in other works he argues that while this is not naturally possible, God can in fact make two bodies to be in the same place.Footnote 31 So, he must not think that this is altogether impossible. Again, Aquinas claims that the existence of angels and heavenly bodies is absolutely necessary, since such things contain no potentiality toward non-existence, and he claims this in the very same passage of the Contra Gentiles in which he argues that the parts of a composite substance’s essence are absolutely necessary.Footnote 32 Yet elsewhere Aquinas makes clear that he thinks God can in fact annihilate the whole of creation, making it so that no creature exists.Footnote 33 So, again he must not think that the non-existence of angels and heavenly bodies is altogether impossible.
Hence, it is crucial to know whether Aquinas thinks that the impossibility of a thing existing without the parts of its essence is only a natural impossibility, that is, impossible by the power of natural agents, or a strictly logical impossibility. Aquinas distinguishes between these two kinds of possibility in his main treatments of God’s omnipotence.Footnote 34 He says that something is ‘possible’ in one sense relative to a thing’s power. It is possible in this sense for a builder to build, for example, since a builder has the active power to build; it is possible for wood to burn, since wood has the passive power to be burned. Yet there is another sense of ‘possible’ that is not relative to any thing’s power but is rather absolute. Something is possible in this sense when the terms of a statement are not mutually contradictory, Aquinas explains. For example, he argues that it is not impossible in itself for something other than God to have always existed, since ‘existing from another’ and ‘always existing’ are not mutually contradictory.Footnote 35 Thus, a creature that has always existed is not absolutely impossible, he thinks. When the terms of a statement are mutually contradictory, however, Aquinas thinks that what it signifies is absolutely impossible, that is, impossible in itself. For example, he says that it would be absolutely impossible for something other than God to have always existed if the thing in question came to exist through a process of change.Footnote 36
In the De potentia, Aquinas says that the contradiction between terms that makes something absolutely impossible is a function of the definition of those terms.Footnote 37 It is not absolutely impossible for no creatures to exist, he says, since the statement ‘no creature exists’ does not imply a contradiction, as it would if not existing were contrary to the definition of a creature. That is, if the definition of a creature included its existence, then the statement ‘no creature exists’ would imply a contradiction and would be absolutely impossible, just like the statement ‘a human being is not a rational animal’, Aquinas says. This already suggests that Aquinas thinks of anything contrary to a thing’s definition as absolutely impossible. Indeed, he says that such self-contradictory statements are in themselves unintelligible and inconceivable.Footnote 38 And in the De potentia, he says that such absolutely impossible things are not naturally subject to any power.Footnote 39 In other words, nothing – not any creature nor even God – has the power to bring them about.Footnote 40 Not even a miracle can make contradictory things true, Aquinas thinks.Footnote 41
This brings me to Aquinas’s treatments of the logical limits of God’s power. Aquinas’s major treatments of God’s power all take the same basic line.Footnote 42 For Aquinas, a thing acts insofar as it is actual. Hence, the limits on a thing’s power to act are a function of the limits of its own essence, by which it actually exists. If a thing had an unlimited essence or nature, then it would have the power to bring about all the effects suited to that nature. If there existed an unlimited heat subsisting in itself, for example, then it would have the power to produce all the effects of heat. But, for Aquinas, God’s essence is unlimited existence subsisting in itself. Hence, he thinks that God’s power to act extends to bringing about everything that can have the nature of an existent. The only thing that cannot have the nature of an existent, he thinks, is something self-contradictory and thus absolutely impossible in itself. Hence, God’s power to act extends to making anything that does not involve or imply a contradiction. If something does involve or imply a contradiction, then Aquinas thinks that not even God can bring it about, not because God lacks any power, but because the thing cannot possibly exist, and thus cannot be made to exist.
So, it might seem as if, for Aquinas, God’s active power is coextensive with absolute logical possibility: if it can exist in itself, then God can make it exist. The only things impossible for God would then be things impossible in themselves. But, in fact, Aquinas recognizes a further limit on God’s power, since he thinks that some things are impossible, not because they are self-contradictory, but because something contrary to them is necessary. It is in this sense that Aquinas thinks God cannot commit a sin such as lying, for example.Footnote 43 God’s nature is goodness itself: God is essentially good and the ultimate good, and, hence, he necessarily wills his own goodness. Thus, God cannot will anything incompatible with that goodness, such as lying, on pain of contradiction. Of course, lying is possible in itself, since it obviously happens. But lying is impossible for God, since something contrary to lying is necessary for God to do.
Now, although God cannot act contrary to his own nature, Aquinas does think that God can act contrary to a created nature, but only in an importantly limited sense. In the De potentia, Aquinas divides the miracles that God performs into three different categories.Footnote 44 Some miracles are above nature, he says, insofar as no natural thing has the power to bring about the effect in question. This is the case, for example, with God raising the dead to life. Other miracles are outside nature, insofar as no natural thing has the power to bring about the effect in the way that God does. This is the case with Christ turning water into wine. But other miracles are contrary to nature, Aquinas says, in the sense that a disposition for the contrary effect remains in nature. Recall that for Aquinas the term ‘nature’ refers to a thing’s essence insofar as it orders a thing to its proper activities.Footnote 45 Thus, what is contrary to a thing’s nature can be either contrary to its very essence or contrary to the proper activities to which its essence is disposed. But it is only in the latter sense that Aquinas allows that God can act contrary to nature. When God kept the three boys in the fiery furnace from harm, for example, Aquinas says that the power to burn remained in the fire; or when God stopped the water of the Jordan from flowing, he says that the water still retained its weight, that is, its disposition to flow down.Footnote 46 Yet it is crucial to realize that God performing miracles contrary to nature in this sense, by bringing about effects contrary to those that things are naturally disposed to produce themselves, does not involve God making things to be contrary to their very own natures, as if things did not remain what they are by definition. For that is something that Aquinas thinks God cannot do; indeed, this is the only sense in which Aquinas thinks that God’s effects are necessitated.
Aquinas insists that God creates freely by will, and in no way necessarily.Footnote 47 Yet he does think that God’s effects are necessitated in one sense, namely with respect to the natures of the things that God intends to create. If God is to create something, then he must necessarily give it the parts of its own nature, without which it cannot exist. As Aquinas explains:
… something among divine works can be required only on the part of the form that is the end of [God’s] action. For, since it [i.e., the form] is not infinite, it has determinate principles, without which it cannot exist, and a determinate way of existing, as when we say that, supposing God intends to make a human being, it is necessary and required that he grant it a rational soul and an organized body, without which a human being cannot exist.Footnote 48
Aquinas’s example of a human being requiring both soul and body shows that by the necessities of form here, he means ‘form’ in the sense of a thing’s essence or nature, which in the case of composite substances includes both their substantial form and matter.Footnote 49 Although Aquinas thinks that God can act contrary to nature, in the sense of bringing about effects contrary to those that natural things are disposed to produce, he does not think that God can make things exist in a way contrary to their own natures, in the sense of lacking their essences or any parts of their essences, on pain of contradiction. Thus, Aquinas thinks that the essences of things, which their definitions signify, are logically necessary for their existence. This can be confirmed by considering some of the specific questions Aquinas addresses about the limits on what God can and cannot do.
4. Logical limits of omnipotence
It is worth considering some of the specific questions Aquinas addresses about what God can and cannot do, since in response to these questions Aquinas often appeals to the essences of things in order to explain why God cannot make things to be other than they are by definition. This use of a thing’s essence and definition to limit God’s absolute power confirms that Aquinas thinks of a thing’s essence and its parts as strictly necessary for its existence.
Consider, for example, the question whether God can make things to be better than they are. In response to this question in the Summa Theologiae, Aquinas distinguishes between two different kinds of goodness. One kind is of a thing’s essence, he says, as being rational is of the essence of a human being. Another kind is outside its essence, as being virtuous and wise is for a human being. With respect to a thing’s essential goodness, Aquinas says that God cannot make a thing to be better than it is, although he can make something else that is better than it. He then compares this to how God cannot make the number four greater, since if it were greater, it would no longer be four, but another number. ‘For thus the addition of a substantial difference in definitions is like the addition of a unit in numbers, as Aristotle says in book VIII of the Metaphysics’.Footnote 50 It is only with respect to a thing’s accidental goodness that Aquinas allows that God can make a thing to be any better than it is.
In the parallel passage in his early commentary on the Sentences, Aquinas is even more explicit that this limit on God’s power to change the essences of things for the better is a matter of logical necessity. He begins with the same distinction between essential and accidental goodness, giving only slightly different examples, and then offers the same explanation for why God cannot make a thing’s essence any better, employing an even more extended comparison of essences and definitions to numbers. He then concludes:
Hence, just as God cannot make the number three have four units while remaining three … so he cannot make this thing remain the same [thing] and have a greater or lesser essential goodness. For from all these things it would follow that an affirmation and a negation were true at the same time, which God cannot bring about, as was said in dist. 42, q. 2, a. 2.Footnote 51
It is noteworthy that in this more extended response, Aquinas insists that God cannot make a thing’s essence any better or worse without it ceasing to be. Any loss to a thing’s essence makes for a different thing; not even God can make this otherwise, on pain of logical contradiction.
To take another example, consider the question whether God can make an actual infinity of things. When this question comes up in the De veritate, Aquinas decides not to settle it, though he lays out the same framework that he will use to answer it in the Quodlibetal Questions.Footnote 52 In the De veritate, he explains that an actual infinity could be impossible either because of what an infinity is, or because of something other than what an infinity is. If an infinity can actually exist, given the thing’s nature, or if an infinity cannot exist only because of some impediment other than the very notion of an infinity, then God can make an actual infinity, Aquinas says. But if actual existence is incompatible with the very notion of infinity, then not even God can make an infinity actual, he says, ‘just as God cannot make a human being a non-rational animal, since that would make contradictory things to be the case simultaneously’.Footnote 53
In the Quodlibetal Questions, Aquinas begins his reply to the question by distinguishing two reasons to say that God cannot make something, neither of which involves a lack of power on God’s part. One reason has to do with what it means for a thing to be made. For instance, God cannot make a creature that preserves itself in existence, Aquinas says, since the fact that a thing has God as a maker means that it needs God as a preserver. Another reason God cannot make something has to do with what it is that is supposed to be made. For instance, Aquinas says:
… we might say that God cannot make a horse rational. Of course, something rational can be made, given what it means to be made, since some rational things are made. But a horse cannot be made rational, given what a horse is, since a horse is non-rational by definition.Footnote 54
Aquinas goes on to survey a number of opinions about whether the notion of an actual infinity is possible in itself. He ends up siding with Averroes, who argues in his commentary on Aristotle’s Metaphysics that there is no way something infinite can be actual. Aquinas then explains why he thinks the notion of an actual infinity is impossible in itself, concluding, ‘Therefore, just as God cannot make a horse rational, God cannot make an actual existent infinite’.Footnote 55
Aquinas’s reasons for thinking that an actual infinity is impossible in itself are not that important for present purposes, especially since he seems to have changed his mind on the matter.Footnote 56 What is important is to recognize the framework Aquinas uses for dealing with the question. Whether God can make something actually exist has partly to do with what it is that God is supposed to make, since God cannot make something self-contradictory. Aquinas’s paradigm examples of such self-contradictory things are things that are other than they are by definition, such as a non-rational human being or a rational horse. The fact that he thinks that not even God can make things to be other than they are by definition shows that Aquinas considers a thing’s essence, which its definition signifies, to be logically necessary for its existence.
As a final example, consider the question whether God can make accidents exist without a subject, as God is supposed to do in the Eucharist. This question is important to consider because some survivalists have thought that Aquinas’s answer shows that he thinks of essences as dispositional rather than as strictly necessary.Footnote 57 The case of accidents also helps to make Aquinas’s view of essences and definitions clearer. For in fact Aquinas does not think that accidents have essences in the proper sense, nor does he think that an accident can be properly defined. At the beginning of the De ente, after summarizing his view of essences as we saw above, Aquinas immediately points out that since ‘an existent’ is said absolutely and primarily of substances, and only subsequently and with qualification (secundum quid) of accidents, an essence is found properly and truly in substances, while in accidents it is only found in a certain sense and with qualification (secundum quid).Footnote 58 Hence, one cannot argue from things that are true of the essence of accidents to things that are true of the essence of substances, since such an argument would commit the fallacy secundum quid et simpliciter.Footnote 59
There are many reasons that Aquinas thinks that an accident cannot be properly defined. Accidents are defined by addition, Aquinas says, meaning that their definitions include reference to something outside their own genus, namely the substance on which they depend.Footnote 60 Yet, as I explained above, one of the requirements for an essential definition is that it must contain the whole thing, and nothing but the thing, being defined. Hence, accidents cannot be defined in the proper sense, since their definitions include something in addition to them. Another requirement for a thing’s definition, which I have not yet mentioned, is that the parts of the definition must be related as genus and specific difference.Footnote 61 This requirement is the solution to a problem about how the parts of a definition can signify just one thing, a being per se.Footnote 62 Unfortunately, I do not have time now to discuss this further.Footnote 63 The important point to note here is that substance and accident are the most general genera and, hence, cannot themselves be defined in terms of a genus and specific difference, since there is no higher genus that contains them. ‘For a genus is not defined’, Aquinas says, ‘unless it is also a species’.Footnote 64 Hence, an accident cannot be defined in the proper sense. As Aquinas says, ‘some things are not defined, such as quantity and quality and things of this kind, which are not defined because they are the most general genera’.Footnote 65
Given that Aquinas thinks that accidents do not have essences in the proper sense, and that an accident cannot be properly defined, one must be very cautious in trying to draw any conclusions about his view of essences and definitions from his treatment of accidents. Nevertheless, it is telling that in response to the question whether God can make an accident exist without a subject, Aquinas is careful to show that God never makes an accident to be other than it is by definition. In both the Quodlibetal Questions and in the Summa Theologiae, Aquinas considers objections to the miracle of the Eucharist that have to do with the nature and definition of substances and accidents. For a substance is commonly defined as ‘something existing in itself’ and an accident as ‘something existing in a subject’. But in the Eucharist, the accidents of bread are supposed to exist without a subject, which would seem to imply a contradiction, and thus be impossible even by a miracle of God, since an accident would then exist without its definition applying to it, or even with the definition of substance applying to it instead.Footnote 66
In reply to these objections, Aquinas clarifies the definition of substance and accident.Footnote 67 He points out that ‘existent’ is not a genus, and that existence is not part of the essence of any creature. Thus, ‘existing in itself’ and ‘existing in a subject’ cannot be the true definitions of substance and accident. Instead, he says that their true descriptions are, ‘a substance is a thing whose nature is due existence not in something else’ and ‘an accident is a thing whose nature is due existence in something else’.Footnote 68 Hence, even if God makes an accident miraculously exist without a subject, ‘it still does not gain the definition of a substance … nor does it lose the definition of an accident’,Footnote 69 Aquinas insists, since an accident can still be due existence in a subject, even if it does not in fact have it. Like the previous questions we have considered about what God can and cannot do, this way of dealing with the question shows that Aquinas thinks of a thing’s nature and its definition as strictly necessary for the thing’s existence. That is why he is so careful to insist that ‘existing in a subject’ is not the essence and nature of an accident, so that its own definition will still apply to it even when God makes an accident exist without a subject. For Aquinas does not think that even God can make a thing to be other than it is by definition.
The survivalist could try to say here that Aquinas’s way of understanding the essence of substance and accidents shows that he thinks of a thing’s essence or nature as dispositional, at least with respect to its existence. But it is crucial to realize that since existence is not part of any creature’s essence, this essential disposition is to something other than the thing’s essence and its parts. Nothing about Aquinas’s way of defining substance and accidents suggests that he thinks a thing might be merely disposed to have the parts of its own essence, as if a human being might be merely disposed to being rational or material, for example.Footnote 70 Aquinas never says such a thing about the parts of a thing’s essence. Rather, he says explicitly that not even God can make a human being to be non-rational or to exist without an organized body, as quoted above. Aquinas says such things because he thinks of a thing’s essence and its parts as strictly necessary for the thing’s existence. His consistent use of the essences and definitions of things to limit even God’s absolute power to perform miracles confirms this to be the case.
5. Conclusion
Much more could be said about Aquinas’s view of essences and definitions and the limits of God’s power, and more specific questions could be considered about what God can and cannot do. Nevertheless, I hope to have said enough to show that Aquinas thinks of a thing’s essence and definition as strictly necessary for its existence. His use of a thing’s nature and definition to limit God’s absolute power on pain of logical contradiction confirms that he thinks of essences and definitions as strictly necessary, not merely as a matter of natural necessity stemming from the powers of natural agents, but as a matter of strict logical necessity limiting God himself. Not even God can make a thing to be other than it is by definition. Along with corruptionists, most survivalists acknowledge that Aquinas includes matter within the essence signified by a human being’s definition. Yet many of them have claimed that Aquinas sees a thing’s essence and definition as merely normative or natural or typical, so that a human being could still exist without a body after death. I hope to have shown that this view of essences as merely normative, rather than strictly necessary, is not Aquinas’s own. For him, nothing can exist without all the parts of its essence; nothing can be other than it is by definition, not even by a miracle of God. Since he defines a human being as a certain kind of material substance, Aquinas thinks that not even God could make a human being exist without a body. When a human being loses its body at death, therefore, the human being ceases to exist, absolutely speaking. Thus, corruptionism rather than survivalism is more in line with Aquinas’s own way of understanding the necessity of natures or essences, one of his most basic metaphysical principles.
