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And they ask you about the spirit—Say: The spirit is from the affair of my Lord

Qur’an 17:85

Human nature has been a central theme of intellectual and mystical contemplation from ancient times and across civilizations. By virtue of distinctive traits like rationality, knowledge, speech, and moral agency, man was considered a world apart from the rest of nature, and the spirit of man was recognized as something unique and wondrous. In Islam, knowledge of one’s soul is the point of departure for its purification and for attaining divine love, given that an authentic life of piety and altruism emanates from a sanctified soul absorbed in the remembrance of God.

With the advent of modernity, new philosophical commitments brought new terminology and novel theories. What most civilizations traditionally named spirit or soul is often called “mind” today due to the theological implications of the classical terms.1 The branch of modern philosophy that deals with what the medievals called soul is the philosophy of mind, a field of inquiry that relates to many critical issues in both academic and public discourse. For example, is transhumanism—the theory that through science and technology, humans can evolve beyond current physical limitations and elude aging or even death—a genuine possibility if there is such thing as a human soul? Is atheism, which attempts to explain all of reality through materialism, rendered incoherent if man has an immaterial intellect? Do human consciousness, thought, and rationality signify the existence of the soul? With the scientific method as its governing approach to knowledge, modernity has attempted to unpack man’s inner mystery through a variety of somewhat contrasting paradigms, such as neuroscience, Freudian psychoanalysis, behavioral genetics, and evolutionary psychology.2 So much of human culture, society, and even politics hinges on our awareness of ourselves as human beings and our relationship with the world we inhabit. How we understand the mind is central to that awareness.

Historically, Muslim theologians generally espoused an integrative substance dualism of body and soul. As Syed Naquib al-Attas defines, “Man has a dual nature, he is both body and soul, he is at once physical being and spirit.”3 While Muslim scholastics deemed the essence of the soul to be a mysterious divine secret—what the mystic Ibn ʿAjībah (d. 1224/1809) termed “a luminous, lordly subtlety”4—it was evident that the soul is (a) distinct from the body, though deeply integrated with it, and (b) the locus of human consciousness. Yet as spiritual substance, the soul is inaccessible to empirical investigation: consciousness is located in a realm beyond the physical—not in mulk, the corporeal world, but in malakūt, the spiritual world. The question of its artificial replication is for most theists a nonstarter, since human manipulation is limited to the physical domain. The possibility of replicating consciousness (or generally, any feature of the mind) largely emerges from what is termed naturalism—the view that all things and events in nature can be explained physically, even if the hard sciences have yet to discover their explanations, because natural processes take place of their own accord. As an explanatory idea, naturalism is most often associated with materialism—or physicalism—an ontological position which holds that only “physical matter” really exists.5

In Death of the Soul: From Descartes to the Computer, William Barrett has traced the gradual exclusion of mind from intellectual deliberations on reality.6 The seventeenth century inaugurated a new science that viewed the world as a machine, based on a theory of matter that deems physical objects to be composites of particles in empty space. The mechanism of this Newtonian science was coupled with John Locke’s famous distinction between primary and secondary qualities. According to Locke, since physical objects are merely quantifiable aggregates of molecules, they have only “primary qualities” like extension and shape, while “secondary qualities” like color, taste, or sound are absent from the objects-in-themselves and exist only as sensations in people.7 What is “out there” is only the quantitative and measurable. Unsurprisingly, if quality is generally removed from one’s account of what actually exists, then the mind with all of its qualitative features is also susceptible to being reduced to the quantitative brain/body.

The eighteenth century brought another watershed moment with the skepticism of David Hume, who reduced human experience to a succession of sense impressions, and moreover considered the “self” to be nothing more than a bundle of perceptions. Barrett laments, “The I, or ego, suffered here a blow from which the fragmentation of the Modern Age has never rescued it. We live in a world where the flow of sensations, copiously fed to us by all the devices of technology, can virtually turn the ordinary citizen into a heap of perceptions.”8 Barrett notes that Hume’s categorical mistake, though, was to search for the self in objective sense-data rather than to recognize his own subjectivity in that search. Yet subsequent thinkers were captivated by Hume’s ideas; and as technology and the hard sciences rapidly advanced, materialism would emerge as a reigning paradigm for modern science. Nevertheless, in the eyes of many philosophers of mind, materialism has now reached an insurmountable quandary in the question of consciousness.

Physicalist Theories About the Mind

Physicalist theories that attempt to explain mental states include eliminative materialism, behaviorism, identity theory, and functionalism.9

In light of the continued success and explanatory power of modern physics, physiology, and neuroscience, eliminative materialism [EM] denies the existence of psychological states (sensations, thoughts, feelings, etc.): notions like “John is in pain” and “Fred enjoys vanilla ice cream” are eliminated and replaced by “John’s brain is in neural state X” and “Fred’s brain is in neural state Y.” For eliminativists like Paul Churchland, the commonsense view that mental states are real—what he terms “folk psychology”—is simply a theory, and one that is devoid of explanatory power. So he argues that it is a false theory: its history of failure to provide scientifically useful explanations leads to the conclusion that the mental states of folk psychology are merely illusions. However, opponents of this view argue that (a) our psychological states do not themselves comprise a theory but require a theory (or metaphysical worldview) to explain them; and (b) EM as a theory proves incoherent and self-refuting, insofar as its claims that it is true, and that folk psychology is false, reveal intentionality, itself a profoundly salient state of the mind.10 Truth claims are propositional attitudes that EM denies. Acceptance of EM presupposes folk psychology, since EM rejects notions like “acceptance.”

Another materialist/physicalist theory of mind is philosophical behaviorism [PB], according to which psychological states are logically equivalent to “dispositions” of behavior: pain is not a subjective reality, but is only the tendency to wince or cry or say “Ouch!,” etc. To justify PB, proponents adduce as evidence the strong connection between mental states and behavior, which for them can readily be explained as a connection between behavioral dispositions and behavior. To be “in pain” is to be “disposed” to certain behaviors (crying, wincing, …); to be “happy” is to be “disposed” to certain other behaviors (smiling, laughing, …); and so forth.

PB is also supported by the Vienna Circle’s theory of verificationism in the philosophy of language, a theory that was central to the Circle’s broader philosophy of logical positivism, a form of empiricism that denied the possibility of metaphysics. This early twentieth-century group of philosophers and scientists in Vienna, Austria, argued that the meaning of any statement is rooted in its method of verification, and verification was limited to sense-data: if a statement could not be verified empirically, it did not have rational (or “cognitive”) meaning. Thus, some PB proponents argued that if sensory observation is the only avenue of ascertaining the meaning of a proposition, then private mental states can be translated to observable behavior without losing meaning. Most philosophers, though, do not subscribe to verificationism, which has been almost unanimously discarded in the philosophy of language for several reasons, such as the theory’s incoherence—verificationism itself cannot be empirically verified.11Moreover, critics of PB point out that PB is demonstrably flawed, for it is conceivable that a person could have rich and changing mental states yet refrain from any behavior at all.12 Not all pain is expressed through crying or wincing, and not all happiness through smiling and laughing. And quite often, a person’s behavior is informed by innumerable mental states (beliefs, emotions, desires, motives, …) that are near impossible to reduce to algorithms of corresponding physical behavior.

Both EM and PB have generally proven untenable as physicalist theories of mind, leading most materialists to embrace what is termed identity theory [IT]. IT is based on the idea that conceptual differences do not necessarily entail actual distinction between different entities, and that empirical investigation can confirm their shared identity. So, according to proponents like J.J.C. Smart, just as “water” and “H2O,” or “lightning” and “atmospheric electrical discharge,” are conceptually different yet empirically identical, so too are mental states empirically identical to physical brain states despite the conceptual difference between them.13 While subjective, first-person mental states may seem to be vastly different from objective, third-person neuronal states, IT holds that empirical investigation has shown them to be identical.14 IT theorists do not propose merely that mental states are related to or interact with brain states—many forms of dualism will admit as much—but that they are the same thing. IT theorists also do not deny the existence of mental states as EM theorists do. According to IT, experiences of the mind are real, yet they are reducible to operations of the brain, since the two are in fact identical; mental states are physical brain states. The particular feeling I get when my finger gets jammed by the door is held to be identical with some specific activity in my brain (such as “c-fiber firing,” or activation of the neural pathways associated with pain). Even though they differ in sense, “pain” and “c-fiber firing” refer to one and the same reality, so pain is nothing more than c-fiber firing.

One cogent objection to IT is to note the philosophical leap from correlation to identity. Empirical study has certainly demonstrated correlation between, for example, pain and c-fiber firing. Yet as Roger Scruton notes, to assert “identity” would entail that if a c-fiber associated with pain were completely removed from someone’s body and then stimulated in a laboratory, someone or something would be in pain, which is patently false.15 This objection could also be framed within the principle that if A and B are identical, each will have all the properties of the other.16 Yet the conscious experience of pain is to hurt, while c-fiber firing has no property of hurting.

The objection is related to Saul Kripke’s linguistic discussion on “rigid designators,” or terms that denote the same object in any possible world.17 For IT to be true, statements like “Pain is identical to c-fiber firing” would have to be true in every possible world, meaning both sides of the sentence would have to be rigid designators. Yet as the above example shows, we can easily conceive of a world in which c-fiber firing exists without pain, and in which pain exists without c-fiber firing; hence, c-fiber firing is not a rigid designator of pain. In other words, mental experiences and brain activity are simply two different kinds of things, even if strong correlations between the two are discovered. Another related objection is that IT obviates “multiple realization,” or the realization of the same mental states in animals with different neurophysiology: if pain is identical to c-fiber firing, then animals whose pain is found to be associated with the firing of d-fibers (or e-fibers, or f-fibers, etc.) could not in fact experience pain, since pain is identical to the firing of c-fibers.

Based on the multiple realizability objection and other concerns, most materialists came to embrace the theory of functionalism, which is based on the notion that a thing is defined by its function rather than by its substance. Thus, what is conventionally called a “mental state” is only some function in the organism’s behavior—specifically, a connection between environmental input and behavioral output. Multiple realizability can be accommodated: human “c-fiber firing” executes the same function as cat “d-fiber firing,” and “experiencing pain” is but an internal mechanism that carries out that particular function. And a “function” is described by the network of causal relations between environmental stimuli (input) and bodily behavior (output). For example, the function of pain is explained by the connection between a door slamming on one’s finger or a cat’s paw (input) and yelling “Ouch!” or a high-pitched feline sound (output). The function might also incorporate other “mental states,” that is, other functions that are internally connected. So in the example of pain, the input of one’s finger being slammed by a door would be connected to “anger,” which itself is but a function with its own algorithmic connections. The language of “mind” that we humans conventionally use is simply a convenient way of expressing functions. Thus, as a theory of mind, functionalism allows for what John Searle has called “Strong Artificial Intelligence” (Strong AI),18 or the notion that a computer could have genuine mental states, since theoretically it could be programmed to have the same functions exhibited by humans, the same functional connections between stimuli and output. Related to this is Alan Turing’s famous “Turing Test,” which holds that a machine will be deemed intelligent (and conscious) “if it acts so like an ordinary person in certain respects that other ordinary people can’t tell… that it isn’t one.”19

The Intractability of Consciousness

What functionalism excludes of consciousness, however, are essential features like qualia and intrinsic intentionality.

Mental states involve what philosophers call qualia, or the way it feels to be in pain, to enjoy ice cream, or to see red. And certain qualia are features of all consciousness, human or animal. As Thomas Nagel has argued, a scientist who gains mastery of all there is to know about echolocation in bats, of complete bat neuroscience, and of all the functional connections of bat behavior, would still not know “what it’s like to be a bat.”20 There is a first-person feel to that reality that no third-person account can provide. Frank Jackson has made a similar qualia argument21with color: if a scientist who had never seen color were forced to investigate nature from within a black-and-white room, and learned everything about the physical basis of seeing color—“everything in completed physics, chemistry, and neurophysiology, and all there is to know about the causal and relational facts consequent upon all this, including of course functional roles”—she would undoubtedly gain new knowledge of the world were she to go out and see red for the first time. Specifically, as Jackson explains, “she will realize how impoverished her conception of the mental life of others has been all along.”22 Some identity theorists respond that, as IT asserts, the conceptual distinction between qualia and scientific knowledge of related brain processes itself is not evidence of their actual distinction. Yet proponents of knowledge arguments reply that the first-person subjective experience of qualia is still undeniable, and physicalist descriptions of objective neuronal activity leave that out.  Knowledge arguments like these demonstrate that qualia are real, based on the categorical distinction between first-person subjective experience and third-person description. Functionalism is therefore false, and Strong AI incoherent. A computer programmed to mimic human response to stimuli clearly lacks qualia.

Mental states also have intentionality, or a directedness towards something (that is, they are about something): we can think about the universe, or about history, or even about our consciousness, etc. Based on intentionality, John Searle has formulated a thought experiment called “The Chinese Room” that argues against functionalism and strong AI.23 If one were to imagine a person who does not understand Chinese, locked in a room with a rule book (effectively, a computer program) that lists correct answers to questions in Chinese; who receives those questions as input from someone outside the room; and who, based on the rule book, provides perfectly correct answers as output back to the person outside, it remains true that the man in the room still does not understand Chinese, even though the Turing Test was passed successfully from the vantage of the person outside the room. The man in the room is akin to a computer that is programmed to give correct answers to questions in Chinese: neither the man nor the computer understands Chinese. While there is extrinsic intentionality in the form of “function,” or giving correct output in response to input, the intrinsic intentionality of understanding Chinese is notably absent. And intrinsic intentionality is a quintessential, necessary property of thought and consciousness.

Intentionality proves to be one of the remarkable features of consciousness that reveals its obstinacy to physicalist reduction or dismissal. Meaning is mysteriously grounded in the purely mental. As Edward Feser notes, anything physical that exhibits meaning, such as a word or a picture, does so only because of mental agents designating it as meaningful—its intentionality is derived and not intrinsic. In and of themselves, words, pictures, or computer pixels are merely marks on a surface. It is only mind that gives those marks meaning. And like ink marks on paper, brain processes are physical entities/processes inherently void of meaning. Yet the concepts and propositions that comprise thought are undeniably non-physical, abstract, and universal. Feser comments:

Had there been no human beings, the proposition there are no human beings would have been true, even though there would then have been no “sentence in the head” for that proposition to be identical to. Had there been no physical world at all, the proposition there is no physical world would have been true, even though there would then have been no physical entity of any sort for that proposition to be identical to…. [W]hen the mind grasps a concept or proposition, there is clearly a sense in which that concept or proposition is in the mind; but if these things are in the mind and yet… cannot be in the brain, it would seem to follow that the mind cannot be identified with the brain, or for that matter with anything material.24

“The robust features of human consciousness cannot be dismissed in philosophical deliberation, and philosophical deliberation cannot be forced to fit into the narrow assumptions of scientism.”

Indeed, despite the celebrated achievements of the physical sciences, materialism as an all-encompassing worldview has gradually faded, if not altogether failed, in light of those features of the world that cannot be reduced to physical matter—morals, values, purpose, meaning, rationality, aesthetics, and—arguably the most recalcitrant to naturalist reduction—consciousness. The robust features of human consciousness cannot be dismissed in philosophical deliberation, and philosophical deliberation cannot be forced to fit into the narrow assumptions of scientism. These robust features of consciousness, or conscious states, include:

  • Sensation or sentient awareness, whether of external things (through sense-data: sight, smell, taste, hearing, and touch), or of internal states (such as hunger, thirst, pain, and pleasure). Emotions, too—anger, sadness, joy, empathy, and the like—are sensed internally. In fact, one’s very existence is apprehended directly by consciousness.
  • Intellection, including the direct unmediated grasp of first principles, or mediated reasoning through the deduction of conclusions from premises. Noteworthy in this regard is the very foundation of human reasoning: simple apprehension, or the abstraction of universals from particulars, so as to form and understand concepts.
  • Belief, or the internal assent to a proposition and the act of regarding it as true or false, likely or unlikely.
  • Desire or wanting.
  • Memory.
  • Will or choice, meaning the faculty that selects between alternatives so as to act accordingly.
  • Motive, meaning the impetus that propels a person towards or away from an action. 

Many philosophers would include intuition, insight, and what is termed “common sense.”25

All of these features are integrated in the centered self and together inform one’s choice, agency, and experience. Furthermore, human consciousness has the unique property of “awareness of one’s very consciousness”—the profound capacity of self-reflection, wherein consciousness faces itself and “sees” its own awareness, apprehension, realization, and sapience. All of the above features of consciousness are experienced internally and privately by the subject: they are first-person, subjective, and have an undeniable immediacy for the individual. They cannot be described in the third-person or objective language used for what is physical, even if a correlation between mental states and physical states/events in the brain is empirically found.

As we attempt to understand the mind, should we weigh the arguments of philosophy above the theories of science?

A final consideration for the uniqueness of “mind” and its distinctiveness from the physical domain is the unity and simplicity of consciousness. This is a principal rational argument for substance dualism put forth by the Muslim theologian Fakhr al-Dīn al-Rāzī (d. 606/1209) in his treatise on the soul,26 and different versions of it have been used by Descartes, Leibniz, Kant, and others since. Mental awareness is unified and indivisible, expressed by the singular “I” that represents the individual. The brain, however, is composite. It is a collection of physical parts organized in a certain way. And if a composite substance were the locus of consciousness, then each part of the aggregate would have a part of consciousness. Yet consciousness, as denoted by the pronoun “I,” is not divisible into parts. It is what philosophers call “simple.” William Hasker comments, “A person’s being aware of a complex fact cannot consist of parts of the person being aware of parts of the fact [emphasis his]. A conjunction of partial awarenesses does not add up to a total awareness.”27 Likewise, as David Barnett contends, “[F]or any pair of conscious beings, it is impossible for the pair itself to be conscious”; and this is true only because consciousness is simple, while any pair (or group of parts) is composite.28 

The soul, however, is simple indeed. And it is the foundation and basis of the spiritual life of man. The implications of its denial are quite grave, since it is the soul that apprehends meaning, purpose, and virtue. The theologians and mystics of Islam held it to be a secret of the Divine, for only the soul is capable of knowledge—of oneself, of fellow man, of society, of the cosmos, and of its Creator. And only the soul is capable of love. Among its properties are to seek, yearn, and long for goodness, for truth, for beauty, for intimacy, and ultimately for perfection. The enterprise of scientific discovery itself presupposes this immaterial orientation to these immaterial, transcendental realities: the scientist is impelled by a passion to discover what is true, and deems that pursuit good. Metaphysics accommodates transcendentals, as it accommodates consciousness. At bottom, it would seem that consciousness remains intractable to ontological reduction or elimination. While the human body can be described to a great extent in the language of physics and biochemistry, the human spirit cannot. It must be something else.