Metaphysics is the branch of philosophy that studies the nature and structure of reality. Questions metaphysicians ask and try to answer include the following: What exists? How do the different kinds of things that exist relate to one another? What aspects of reality are fundamental and derivative? These questions, and many more like them, have been asked as long as human beings have sought to provide a rational account of the world.
These questions are not trivial. Metaphysics matters. The beliefs we hold about the world shape our experience of the world and our behavior in the world. Even our eternal destinies are at stake, as C. S. Lewis (1898–1963) powerfully illustrates through a series of fictitious letters between a senior devil and a junior/apprentice devil named Wormwood. In the first of these imaginary letters, the senior devil instructs Wormwood as follows:
Jargon, not argument, is your best ally in keeping him [that is, the patient whom they are trying to keep from becoming a Christian] from the Church. Don’t waste time trying to make him think that materialism is true! Make him think it is strong, or stark or courageous—that it is the philosophy of the future. . . . The trouble about argument is that it moves the whole struggle onto the Enemy’s [God’s] own ground. He can argue too; whereas in really practical propaganda of the kind I am suggesting He has been shown for centuries to be greatly the inferior of Our Father Below. By the very act of arguing, you awake the patient’s reason; and once it is awake, who can foresee the result? Even if a particular train of thought can be twisted so as to end in our favour, you will find that you have been strengthening in your patient the fatal habit of attending to universal issues and withdrawing his attention from the stream of immediate sense experiences. Your business is to fix his attention on the stream. Teach him to call it “real life” and don’t let him ask what he means by “real.”1
The book, of course, was Lewis’s classic The Screwtape Letters. He painted for us, in a wonderfully delightful way, a picture of the battle taking place between the forces of good and the forces of evil over humans’ beliefs regarding the nature of reality.
This battle over the nature of reality has been going on for some time.2 In the Sophist, Plato describes “something like a battle of gods and giants,” an interminable “dispute” over the nature of reality. In one camp, the giants “drag everything down to earth from the heavenly region of the invisible,” arguing that true reality is found only in the world of our sensible experience. In the other camp, the gods maintain that “true being is certain nonbodily [i.e., immaterial] forms.”3 In our own day, the battle over the nature of reality continues to rage. For example, in a well-known series of lectures delivered in 1960 at the University of Pittsburgh, the philosopher Wilfrid Sellars distinguishes between the “manifest image” of the world—our ordinary perception of the world as rational, beautiful, and mysterious—and the “scientific image” of the world, a disenchanted world of mathematical formulas, particles in motion, and blind forces.4 Sellars argues that the two perspectives of the world are incommensurate and that our manifest image—the world of “appearance”—is not the world in reality; in reality, the world is the complex physical system of the “scientific image.”
In this chapter we shall consider, in broad outline, three prominent views about ultimate reality, highlighting their merits and drawbacks, as we seek to answer our fundamental questions about the nature and structure of reality.5 We begin with perhaps the dominant views of our day, the view of Plato’s giants and Sellars’s “scientific image.”
According to materialism, everything that exists is material. The material cosmos is “one gigantic spatio-temporal whole,” composed of (in ascending order) particles, molecules, medium-sized objects, planets, stars, and galaxies.6 Materialism is a kind of monism. There is just one kind of thing that exists: the material thing.
Closely associated with this theory of reality is a theory of knowledge called empiricism. Roughly, empiricism is the idea that all knowledge is of the sense-perceptible kind. It is currently more fashionable to speak of “the scientific” instead of “the sense perceptible,” and thus many in our culture who adopt a materialistic metaphysics also adopt a theory of knowledge called scientism.7 According to a particularly strong version of scientism, all knowledge comes from the deliverances of science. If you want knowledge, you must turn to the scientist.
For the materialist, notice the tight connection between epistemology and metaphysics, as articulated by the philosopher Alex Rosenberg: “If we’re going to be scientistic, then we have to attain our view of reality from what physics tells us about it. Actually, we’ll have to do more than that: we’ll have to embrace physics as the whole truth about reality.”8 Science today, as Rosenberg’s comment shows, is exalted as the paradigm of rationality. If you want to be reasonable (and who doesn’t?), then you must be scientistic, and if you are going to be scientistic, then you must embrace that all of reality is captured by physics. Rosenberg continues: “Why buy the reality that physics paints? Well, it’s simple, really. We trust science as the only way to acquire knowledge.”9 This is a bold statement, especially since it is self-defeating!10 But let that pass. We want to notice one implication of scientism as a theory of knowledge and materialism as a theory of reality: naturalism, the view that there is no supernatural aspect to reality. As Rosenberg concludes, since physics tells us everything about reality, “that is why we are so confident about atheism.”11 Thus if materialism is true, then so is naturalism: there is no God, no immaterial soul, and no abstract reality (more on this below).
The materialistic view of reality has a lot going for it. As already noted, it is widely thought to be the view of reality backed by the scientific enterprise. Given the fact that science is often equated with reason, there are strong sociological factors for thinking materialism to be true. No one, after all, wants to be labeled as antiscience. Moreover, philosophically, materialism is a simple theory, positing one kind of thing only, the material; since simplicity is a theoretical virtue (and hence truth indicative), we have a reason to think that materialism is rationally preferable to its competitors.
Materialism is not without problems, however. One theoretical virtue, such as ontological simplicity, must be weighed against other theoretical virtues, including explanatory power and scope. Many argue that materialism fails miserably in its ability to adequately explain many of the phenomena of the “manifest image”—in particular, facts about human persons and their mental lives.12
Two features of our mental lives that seem to be at odds with a materialist metaphysics are the first-person perspective and intentionality. When I (Paul) say I am hungry, I am in pain, I am here, and the like, I am reporting something about which I cannot be mistaken. I have privileged access to these mental states. They are mine. I am a self-conscious agent who can refer to myself using indexicals such as “I” and “here” and “now.” However, as Thomas Nagel has pointed out, there is no place for indexicals in science: a complete scientific description of the world, identifying all particles and forces and their locations in space and time (from a third-person perspective) would leave something out: me.13 As Roger Scruton states, “Science cannot tell me who I am, let alone where, when or how.”14
Intentionality is the “aboutness” or “ofness” of my mental life. I have a thought of my wife, a belief about London, a hope for the afterlife. This aboutness that characterizes our mental life is, again, very difficult to account for on a purely materialistic metaphysics. Materialists typically try to reduce intentionality to physical causal relations of input and output.15 My thought of London is reduced to certain inputs (I see a picture of Big Ben), which in turn produce an output, a certain behavior, such as my claiming that London is a grand city. John Searle, however, has advanced the famous Chinese Room Argument, showing how attempts to explain intentionality in terms of physical causal inputs and outputs fails.16 What is left out, according to Searle, is genuine understanding: physical inputs and outputs can mimic understanding, but they do not possess it, and thus they do not adequately account for the phenomenon of intentionality. Moreover, intentionality possesses qualities that physical states do not (e.g., intentionality can be about nonexistent entities; physical causal relations hold only between existent entities), and this provides reason to think that intentionality cannot be reduced to the purely material.17
A deeper problem for materialism concerns its intelligibility. As Lewis puts it, “Thus a strict materialism refutes itself for the reason given long ago by Professor Haldane: ‘If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true, . . . and hence I have no reason for supposing my brain to be composed of atoms.’”18
Lewis is noticing a deep conflict between materialism and the reliability of our cognitive faculties. More recently, Alvin Plantinga has advanced a more rigorous argument highlighting the self-defeating nature of materialism.19 The basic idea is this: The conjunction of materialism and evolution means that our cognitive faculties select beliefs for their survival value rather than truth. But then, if my beliefs are selected for their survival value and not truth, I have no good reason to think my beliefs are true. But then, if I have no good reason to think my beliefs are true, I have no good reason to think materialism is true. Therefore if materialism is true, I have no good reason to believe materialism is true. Materialism is self-defeating.
While much more could be said, we offer one final thought. If Christian theism is true, then materialism is a nonstarter. If God, an immaterial self-conscious substance, exists, then materialism is false. Moreover, if theism is true, advances in science are just discoveries of the world that God has created, not evidence for materialism.
Dualism
Metaphysical dualism is the view that two kinds of things exist in the world. One prominent form of metaphysical dualism is called Platonism, roughly the view that in addition to the material cosmos, there exists an abstract realm of nonmaterial objects. Platonism, as the name implies, has its roots in the thought of Plato (427–347 BC), who argued that reality is constituted by a visible world, which is temporal, changing, and contingent, and by an invisible world of the Intelligible Forms, which is eternal, unchanging, and the source of all in the visible realm.
Another prominent form of metaphysical dualism, advocated in the seventeenth century by René Descartes (1596–1650), is called substance dualism. According to substance dualism, each human is composed of two basic kinds of substances, an immaterial soul and a material body. Descartes argued that the body operates according to mechanical laws of nature and is extended through and located in space. The soul, however, has no spatial location or extension; is that which thinks, feels, and wills; can survive the death of the body; and causally interacts with the body through the pineal gland (located in the brain).
Finally, Christian theism is another important kind of metaphysical dualism. As noted above, according to Christian theism there exists, in addition to the material cosmos, an immaterial divine substance. Since the viability of substance dualism and God’s existence are discussed in detail in chapters 11, 12, and 15, in the remainder of this section we shall focus on Platonism and the claim that, in addition to the spatiotemporal universe, there exists an abstract realm of reality populated by entities such as properties, relations, propositions, sets, numbers, states of affairs, possible worlds, and the like.
It will be helpful to first understand just what an abstract object is and how it differs from a concrete object. While the issue is debated, there is somewhat of a consensus among philosophers as to the following: An abstract object is a nonspatial, nontemporal, necessarily existing,20 causally impotent entity. A concrete object—a table, chair, rock, electron, or star—is defined, in contrast, as that which is not abstract.21
Why think that abstract objects exist? Two important arguments for Platonism are the One over Many Argument, to be discussed in chapter 8, and the Indispensability Argument, which we shall explore here. The Indispensability Argument can be formulated as follows:
Consider familiar sentences of the form “a is F” such as “The apple is red” or “Socrates is wise.” In these sentences, the subject terms—the apple and Socrates—are the singular terms, and if these singular terms are part of a true sentence, then it is reasonable to think that the objects referred to by way of these singular terms really exist. If it is true that “the apple is red,” then the object denoted by the singular term—the apple—really exists and is red. (In chap. 8 we’ll discuss the question of what to do ontologically with the predicate “is red.”) If it is true that Socrates is wise, then the object denoted by the singular term—Socrates—really exists and is wise. Premise 1 rests on a criterion of ontological commitment, in a tradition that broadly follows the work of Willard V. O. Quine, such that we are ontologically committed to singular terms and existential expressions (we focus here only on singular terms) of literally true simple sentences.23
Regarding premise 2, consider the sentences “Two is prime” and “Courage is a virtue.” Assuming both are true, the singular terms refer, according to the criterion of ontological commitment, to the objects denoted by the singular terms. But in this case, the objects denoted by the singular terms are not concrete objects: they are abstract objects—the number two and the property courage, or being courageous. Thus if the criterion of ontological commitment is true and there are true atomic sentences in which the singular term can be understood only as an abstract object, it follows that abstract objects exist (and Platonism is true).
Since the Indispensability Argument is valid, the nominalist, who denies the existence of abstract objects, must deny either premise 1 or premise 2. William Lane Craig, for example, rejects premise 1 and the criterion of ontological commitment that undergirds it. Craig finds it astonishing that so many philosophers take existential expressions (“There is/are”) and singular terms to be ontologically committing. When considering singular terms, Craig argues, “Far too many philosophers, I think, are still in the thrall of a sort of picture theory of language according to which successfully referring terms have corresponding objects in the world.”24 To support this claim, Craig lists example sentences, such as “Wednesday falls between Tuesday and Thursday” or “He did it for my sake and the children’s,” arguing that it would be absurd to think that there really are Wednesdays or sakes in the real world. Craig thinks singular terms that refer to real-world objects are probably the exception rather than the norm.25
We are in deep waters here. Questions about how to establish whether something exists, what “ontological commitment” means, and the relationship between language and the world are perennial topics of philosophical dispute. By way of reply to Craig, it won’t do simply to assert the unbelievability of a thesis. The fact that Craig finds such recondite objects as Wednesdays or sakes as absurd is beside the point. What is needed are philosophical reasons for thinking that the criterion of ontological commitment is defective. One advantage of the Quinean approach to ontological commitment is that it offers a clean and straightforward way to determine what exists: “to be is to be the value of a bound variable” (for existential claims), or “the function of a singular term is to refer to existent objects.”26 For certain kinds of Meinongians, who think existential expressions and singular terms are not ontologically committing in any sense, the question becomes, How, given your view, do we establish that something exists?27 Whatever answer is given to this question may prove more troubling than the Quinean approach.28
Two prominent attempts to reject premise 2 are (a) the paraphrase strategy, which accepts the truth of the sentences in question yet finds a nominalist-friendly paraphrase that gets rid of the purported abstract object; and (b) the fictionalist strategy, which holds that the sentences in question are literally false and thus do not denote abstract objects.29 According to paraphrase nominalism, sentences such as “Two is prime” and “Courage is a virtue” can be paraphrased without loss of meaning as, for example, “If there were numbers, two would be prime” and “Courageous persons are virtuous persons.”30 As long as the paraphrase removes the troubling entity (the number two, the property being courageous) without a corresponding loss of meaning, we have found a nominalistically acceptable sentence. The problem, however, is that the proposed paraphrases, and many others, seem to fail. As Balaguer observes, the proposed paraphrases do not seem to capture the ordinary meaning of such simple sentences. “Two is prime” is about the number two, whereas the proposed paraphrase is about what would be the case if there were numbers.31 With respect to the sentence “Courage is a virtue,” the proposed paraphrase doesn’t even share the same truth value (and thus, again, does not share the same meaning). While “Courage is a virtue” is a necessary truth, the truth value for the sentence “Courageous persons are virtuous persons” is contingent: it could turn out that a courageous person is in fact not virtuous, given moral or intellectual vices in other areas.32
The fictionalist isn’t worried about translating sentences into proper nominalistic form. Rather, all sentences that appear to commit us to the existence of abstract objects are false. The sentences “Two is prime” and “Courage is a virtue” should be treated the same way as the sentence “Oliver Twist is an orphan.” Oliver Twist doesn’t exist, yet we can still coherently make reference to him as long as we understand that we are talking about a fictional character in a story written by Charles Dickens. In the same way, argues the fictionalist, we are to construe talk about numbers, properties, and the like as make-believe. The fictionalist proposal strikes many as implausible. It seems too easy: if you don’t like the ontological implications of certain sentences, then just deny that the sentence is true. However, it seems obvious that “Two is prime” or “Courage is a virtue” are true, and necessarily so. For these reasons, while there are sophisticated proposals on offer, many are unwilling to follow the fictionalist down the antirealist path.33
Idealism
The final view of ultimate reality we shall consider is idealism. While there are many versions of idealism, we shall focus on a particularly influential one developed by the British empiricist George Berkeley (1685–1753). The only kind of things that exist, according to Berkeleyan idealism, are mental things: minds and ideas. To be is to be perceived or to be a perceiver.34 While the denial of material objects seems to go against common sense, idealism is important to consider for at least two reasons. First, the arguments in favor of idealism are a good bit stronger than one might initially suppose and thus warrant further investigation. Second, there is renewed interest in Berkeleyan idealism today, particularly among Christian theologians and philosophers, and thus it is important to understand why Christians in particular find this theory of reality attractive and superior to its competitors.35
The starting point on the path toward idealism is the modern era’s debate over the nature of perception. A commonsensical theory of perception, called direct realism, holds that what one is directly aware of in perceptual experience is a mind-independent reality. For example, in perceiving the table, I am directly aware of the table itself. The problem with direct realism is that it does not seem to adequately account for special cases, such as illusion. Consider a straight stick that appears bent when placed in water. If the object of perceptual experience is the stick itself, then according to direct realism there should be no difference between appearance and reality.
In order to handle the problem of illusion, early modern philosophers such as Descartes and John Locke (1632–1704) advocated a theory of perception called representative realism. According to representative realism, in perception we are directly aware of a mental item—our sensory ideas—and indirectly aware of a mind-independent reality. We perceive physical objects—tables, rocks, trees—by way of our sensory ideas. By making a distinction between direct and indirect awareness, the representative realist can account for why, in the case of illusions, reality and appearance are distinct. For example, in the case of the straight stick, in normal circumstances the only medium between the stick and our sensory idea of the stick is the air. In the illusory case, however, the additional medium of water causes the light from the bottom part of the stick to refract, generating a difference between our sensory idea of the stick and the stick as it is in reality.
Berkeley agreed with the representative realist that the objects of our direct awareness are sensory ideas. He disagreed, however, that the objects of our sensory experience point beyond themselves to some mind-independent reality. This is because in the end, argued Berkeley, representative realism leads to skepticism. How, he asked, could we ever know that our sensory idea of a table is caused by a mind-independent table instead of a mad scientist or an evil demon? By arguing that there is only the mind-dependent reality of sensory ideas, the threat of skepticism is removed once and for all. It is important to emphasize: Berkeley is not denying that tables, rocks, and trees exist. He is simply denying their mind-independence. Physical objects are collections of ideas. Whose ideas? For Berkeley there could be only one answer: God’s ideas. Thus there are, according to Berkeleyan idealism, two kinds of minds, divine and nondivine, and two kinds of ideas, sensory and imaginary (sensory ideas are “given”; we are passive recipients of them, whereas imaginary ideas are ideas that we “dream up” or produce through the activity of thinking).
Berkeleyan idealism, with its focus on the primacy of the mental, has a lot working in its favor, particularly for the Christian theist. For example, as a version of substance monism (only immaterial substances exist), it is simpler than pluralistic ontologies, such as metaphysical dualism; all things being equal (i.e., assuming the two types of ontologies are explanatorily on par), simplicity counts in its favor. Moreover, the idealist theory of perception is argued to be more consistent with the findings of quantum mechanics and is immune to skepticism since what we are directly aware of in perception is the mind-dependent physical reality.36 Finally, if, as its adherents claim, it is consistent with Christian orthodoxy, then, contrary to initial reactions, idealism is a viable option for many theists.
However, Berkeleyan idealism is not without problems. On reflection, it is not obviously simpler than its dualist competitors. For example, idealists argue that the problem of causal interaction between immaterial and material substances dissolves under idealism, since all causal interactions are between mental objects only.37 Unfortunately, the causal interaction problem is not solved: it is relocated.38 Consider the age-old mind-body problem. The question becomes, How does my mind enjoy two-way causal interaction with the collection of divine ideas that is my body? If, as those following Berkeley think, occasionalism is true, then the interaction problem dissolves again (since God is the only causal agent in the universe), but the explanatory benefits accrued to the idealist are negated (for many philosophers) by an unattractive theory of causation. Moreover, in the end it is not clear that Berkeleyan idealism is consistent with Christian orthodoxy. Consider this: if divine ideas are part of God (and how could they not be?) and physical objects are collections of divine ideas, then physical objects are part of God. But then creation is part of God, panentheism is true, and Christian orthodoxy is called into question.39 Finally, it could be argued that there are more sophisticated versions of direct realism that handle the problem of illusion (and other related issues) adequately. If so, then a chief motivation for idealism is significantly undercut.40
Conclusion
In this chapter we’ve explored three prominent views of reality: materialism, dualism, and idealism. Each view has something going for it as well as certain costs or problems that need to be overcome. Given Christian theism, we think that materialism is a nonstarter. We’re not particularly attracted to idealism either but think it should be given its due. For our part, we can learn from the materialist to value the physical world—in its beauty, diversity, and abundance—as part of the giftedness of creation. We can also learn from the idealist to remember the primacy of the spiritual or immaterial. Mind is before matter in a very important sense because God—an immaterial Mind—is the source of all concrete finite reality. Moreover, there is more to life than the constant stream of sensual and physical experience. There are immaterial and spiritual goods too, including, most importantly, communion with God through the union of our finite spirit with the infinite Spirit. Much more, of course, can be said about each of these views and more besides. What should be clear is that the interminable battle over the nature of reality shows no signs of waning anytime soon.41
1. C. S. Lewis, The Screwtape Letters (Westwood, NJ: Barbour Books, 1990), 11–12.
2. Given Christian theism, it could be argued that this battle over reality has been going on since at least the fall of Adam and Eve.
3. Plato, Sophist 246a–c, in Plato: Complete Works, ed. John M. Cooper (Indianapolis: Hackett, 1997), 267–68.
4. These lectures were later published in Wilfrid Sellars, Science, Perception, and Reality (London: Routledge & Kegan Paul, 1963), 1–40.
5. While discussing materialism, dualism, and idealism, in rough outline we follow Steven B. Cowan and James S. Spiegel’s discussion of ultimate reality in The Love of Wisdom (Nashville: B&H, 2009), 152–72.
6. Reinhardt Grossmann, The Existence of the World: An Introduction to Ontology (New York: Routledge, 1992), 8.
7. Dallas Willard, “Knowledge and Naturalism,” Naturalism: A Critical Analysis, ed. William Lane Craig and J. P. Moreland (New York: Routledge, 2000), 25.
8. Alex Rosenberg, The Atheist’s Guide to Reality: Enjoying Life without Illusions (New York: Norton, 2011), 20 (emphasis in original).
9. Rosenberg, Atheist’s Guide to Reality, 20.
10. Notice that the claim “Science is the only way to acquire knowledge” is itself a piece of knowledge. But importantly, this piece of knowledge is not a deliverance from science. Rather, it is a philosophical statement about the nature of knowledge. But then, if scientism is true, it is false. It is self-defeating. So there is, contrary to Rosenberg’s claim, at least one piece of knowledge that does not come from science. If there is one piece of knowledge, it is reasonable to think there may be other pieces of knowledge from nonscientistic sources.
11. Rosenberg, Atheist’s Guide to Reality, 20.
12. Other phenomena that are difficult to explain in a materialistic metaphysic include free will (see chap. 10); morality (see chap. 16); knowledge (see chaps. 2 and 3); meaning (see chap. 17); the unity amid the diversity in the world (see chaps. 8 and 9); and the origin of the universe itself (see chap. 12).
13. Thomas Nagel, The View from Nowhere (New York: Oxford University Press, 1986). Cited in Roger Scruton, The Soul of the World (Princeton: Princeton University Press, 2014), 31.
14. Scruton, Soul of the World, 31.
15. For more, see J. P. Moreland, The Recalcitrant Imago Dei: Human Persons and the Failure of Naturalism (Norwich, UK: SCM, 2009), 92–95.
16. John Searle, “Minds, Brains, and Programs,” Behavioral and Brain Sciences 3 (1980): 417–57.
17. For a discussion of six differences between intentionality and physical states, see Moreland, The Recalcitrant Imago Dei, 91–92. For another argument from the reality of conscious intentional states to the falsity of materialism, see Laurence BonJour, “Against Materialism,” in The Waning of Materialism, ed. Robert C. Koons and George Bealer (Oxford: Oxford University Press, 2010), 15–21. For a sustained argument that the reality of consciousness cannot be accounted for by a materialist metaphysic of human persons, see the collection of essays included in Waning of Materialism. As the editors state in the introduction, “It is . . . surprising [given the supposed dominance of a materialist metaphysics regarding human persons] that an examination of the major philosophers active in [philosophy of mind over the last sixty years] reveals that a majority, or something approaching a majority, either reject materialism or had serious and specific doubts about its ultimate viability.” Waning of Materialism, ix.
18. C. S. Lewis, Miracles (New York: Touchstone, 1975), 24.
19. See, e.g., Alvin Plantinga, Where the Conflict Really Lies (Oxford: Oxford University Press, 2011), chap. 10.
20. This sets aside sets with contingent members, which are traditionally considered abstract but nonnecessary.
21. See, e.g., J. P. Moreland, Universals (Montreal: McGill-Queen’s University Press, 2001), 17–18; Grossmann, Existence of the World, 7; and E. J. Lowe, The Possibility of Metaphysics: Substance, Identity, and Time (Oxford: Clarendon, 1998), 212–13.
22. This formulation of the Indispensability Argument is from Mark Balaguer, who calls this “The Singular Term Argument” in “Platonism in Metaphysics,” in The Stanford Encyclopedia of Philosophy, ed. Edward N. Zalta, last modified March 9, 2016, §4, http://plato.stanford.edu/entries/platonism. The Indispensability Argument is historically associated with Willard V. O. Quine and Hilary Putnam and was originally formulated as an argument for the reality of abstract objects within mathematics. For other formulations of the Indispensability Argument, see Mark Colyvan, The Indispensability of Mathematics (New York: Oxford University Press, 2001).
23. See Willard V. O. Quine, “On What There Is?,” in From a Logical Point of View (Cambridge: Harvard University Press, 1953), 1–19. Quine thought we are committed ontologically only by existential expressions and not singular terms, but as Balaguer notes, most philosophers today consider both singular terms and existential quantifiers to be ontologically committing when considering a broadly Quinean criterion of ontological commitment. See Balaguer, “Platonism in Metaphysics,” §4. In fact, simple sentences with singular terms seem to entail true existential expressions; for example, “The apple is red” logically entails “There is something that is red.”
24. William Lane Craig, “Anti-Platonism,” in Beyond the Control of God? Six Views on the Problem of God and Abstract Objects, ed. Paul M. Gould (New York: Bloomsbury, 2014), 121.
25. Craig, “Anti-Platonism,” 121.
26. For a defense of the Quinean criterion of ontological commitment, see Peter van Inwagen, “Being, Existence, and Ontological Commitment,” in Metametaphysics: New Essays on the Foundation of Ontology, ed. David J. Chalmers, David Manley, and Ryan Wasserman (Oxford: Oxford University Press, 2009), 472–506.
27. For more on Meinongians (named after Alexius Meinong, 1853–1920) and linguistic approaches to ontology, see Matti Eklund, “Metaontology,” Philosophy Compass 1, no. 3 (2006): 317–34.
28. With respect to existential expressions, Craig favors a theory defended by Jody Azzouni called neutralism, where the quantifier of first-order logic does not imply any ontological commitments, and a deflationary theory of reference (defended by Arvid Bave) with respect to singular terms, where a person can use singular terms without thereby committing to the existence of the objects to which one is referring. See Craig, “Anti-Platonism,” 119–23.
29. Balaguer, “Platonism in Metaphysics,” §4.1.
30. The first, according to Balaguer, is an example of what is known as if-thenism (“Platonism in Metaphysics,” §4.1). The second is discussed by Michael J. Loux, Metaphysics: A Contemporary Introduction, 3rd ed. (New York: Routledge, 2006), 57–58.
31. Balaguer, “Platonism in Metaphysics,” §4.1.
32. Loux, Metaphysics, 57–58.
33. For a sophisticated defense of fictionalism that tries to dispense with numbers in science, see Hartry Field, Science without Numbers (Princeton: Princeton University Press, 1980). For a robust defense of nominalism with respect to the Indispensability Argument, see Craig, “Anti-Platonism,” in Beyond the Control of God?, chap. 4, including the response to Craig by Keith Yandell, Paul M. Gould, Richard Brian Davis, Greg Welty, Scott A. Shalkowski, and Graham Oppy.
34. The classic articulation and defense of Berkeleyan idealism can be found in George Berkeley, Principles of Human Knowledge and Three Dialogues, ed. Howard Robinson (New York: Oxford University Press, 1999).
35. For recent works by Christian theologians and philosophers defending Berkeleyan idealism, see the two-volume series Idealism and Christianity, with James S. Spiegel as general editor, published in New York by Bloomsbury in 2016: vol. 1, Idealism and Christian Theology, ed. Joshua R. Farris and S. Mark Hamilton; vol. 2, Idealism and Christian Philosophy, ed. Steven B. Cowan and James S. Spiegel.
36. For a discussion of quantum mechanics and idealism, see especially Howard Robinson, “Idealism and Perception: Why Berkeleyan Idealism Is Not as Counterintuitive as It Seems,” in Cowan and Spiegel, Idealism and Christian Philosophy, 84–87.
37. James Spiegel argues this way in “Idealism and the Reasonableness of Theistic Belief,” in Cowan and Spiegel, Idealism and Christian Philosophy, 16–17.
38. It could be argued that the interaction problem is about how two radically different kinds of substances, material and immaterial, interact and thus, by removing material objects from the furniture of the world, idealism does dissolve the interaction problem. If this is correct, the general point still stands; however, another kind of problem surfaces, a near cousin of the original, now over how an immaterial substance relates to the collections of divine ideas that constitute its material body. The latter problem is not the same as the former, but it is within the vicinity of it, and the question of how two radically different kinds of things interact still stands.
39. For a defense of the orthodoxy of Christian idealism with respect to panentheism, see Adam Groza, “Idealism and the Nature of God,” in Cowan and Spiegel, Idealism and Christian Philosophy, chap. 6.
40. For more sophisticated contemporary defenses of direct realism, see J. P. Moreland and Garrett DeWeese, “The Premature Report of Foundationalism’s Demise,” in Reclaiming the Center, ed. Millard J. Erickson, Paul Kjoss Helseth, and Justin Taylor (Wheaton: Crossway, 2004), chap. 4; and Dallas Willard, “How Concepts Relate the Mind to Its Objects: The ‘God’s Eye View’ Vindicated,” Philosophia Christi 1, no. 2 (1999): 5–20.
41. Thanks to Ross Inman for comments on an early draft of this chapter.