When Mind and Body Divorce
Contemporary psychology, despite its methodological advancements and empirical achievements, suffers from a foundational fracture: an inadequate understanding of the mind-body relationship. This is not a minor issue—it cuts to the heart of what psychology purports to study: the human person. As we will see in this article, this defect distorts not only theories but also therapeutic practices. And yet, many psychologists proceed as though the clarification of this were either solved by neuroscience or irrelevant to empirical study.
Why is the mind-body problem so intractable in modern psychology? What philosophical missteps led to this impasse? And can the Aristotelian-Thomistic tradition offer a clearer path forward?
How Mind and Body Got Divorced
Modern psychology's inadequate view of the mind-body relationship is not accidental. Its roots can be traced to Cartesian dualism and the positivism’s turn. Descartes split the human into two substances: res cogitans (thinking substance, i.e., mind) and res extensa (extended substance, i.e., body). While he never denied the soul, he disconnected it from the body in ways that would haunt psychology for centuries.
Cardinal Mercier and Brennan observed that this dualism birthed two oposite conceptions: spiritualism, which treated the mind as immaterial and separate from the body, and materialism, which reduced all mental activity to brain mechanisms. Both shared a fatal flaw: they severed the intimate unity of body and soul. Psychology, caught between these poles, oscillated wildly—first becoming introspectively idealist, then empirically behaviorist, ultimately losing sight of the integrated human subject.
This confusion intensified in the 20th century as psychology sought scientific legitimacy. Behaviorism declared consciousness unobservable and therefore unscientific, focusing solely on stimulus-response patterns. Later, neuroscience picked up the baton, reducing mind to brain, and brain to synaptic activity. Yet as Brennan and Gruender remind us, these trends obscure more than they illuminate. They explain the “how" of certain functions —reaction times, chemical correlates of mood— but cannot answer the “who" behind them.
Why Is This Troubling?
Theoretical Confusion
Modern psychology has become entangled in theoretical contradictions. Caught between reductive materialism and disembodied dualism, it struggles to offer a coherent account of the human person. If the mind is merely an emergent property of neural activity, how can it explain self-awareness, moral responsibility, or the experience of meaning? Conversely, if the mind is an immaterial substance entirely separate from the body, how do immaterial choices cause bodily actions? In either case, psychology finds itself unable to articulate a unified vision of the person.
This fragmentation is especially evident when it comes to personal identity. Without a unifying principle such as the soul, psychology cannot explain what persists through the constant flux of neural states, emotions, and physical changes. In words of Hubert Gruender, this is the first stumbling block of materialism: the inability to account for the stable “I” that remembers, chooses, and hopes.
The faculties of intellect and will also resist reduction to mere brain functions. Brennan noted that intellectual activity involves the apprehension of universals and the pursuit of truth—capacities that transcend sensory data and cannot be explained by material processes alone. Treating these faculties as epiphenomena or higher-order computations empties them of their essential immaterial nature, leaving psychology unable to do justice to what makes human beings rational and moral agents.
Clinical Impoverishment
These theoretical deficiencies have direct consequences for clinical practice. When psychology reduces the person to biological mechanisms or behavioral patterns, it loses sight of the interior life. Depression, for instance, is frequently treated as a mere “chemical imbalance,” ignoring the existential and spiritual dimensions that often lie at its core. In doing so, therapy risks becoming a technical intervention devoid of moral or personal depth. Even effective methods like cognitive-behavioral therapy are in danger of addressing symptoms without engaging the person, all because they rarely asks deeper question that involves considering the patient as a whole.
Furthermore, a psychology grounded solely in biological or behavioral frameworks overlooks the patient’s longing for meaning. As Brennan warned, in the absence of a unified framework, psychological data remain unanchored—deprived of interpretation and unable to contribute to a coherent vision of human flourishing. As a result, therapy becomes disjointed, incapable of addressing the full depth of human experience. Ultimately, this culminates in a profound loss: the disappearance of the person from the therapeutic encounter.
Body and Soul as One Substance
In contrast to both dualism and reductionism, Aristotle and Aquinas offer a unified view: the soul is the form of the body. It is not a separate substance, nor merely a function, but the principle of life, unity, and identity in the human being. Anima forma corporis—the soul is what makes the body a human body. It should come as no surprise that Brennan insists that all psychological data must be interpreted in light of this fact.
In accordance with this, mental acts are neither ghostly nor purely material. They are acts of a rational soul operating through a body. Thus, imaging studies showing neural correlates of decision-making do not threaten free will; they reflect the soul’s activity as expressed through bodily organs. As Mercier notes, only a metaphysics that affirms a substantial union can make sense of how thought, emotion, and will manifest bodily, yet remain irreducibly spiritual in their higher operations.
Toward Whole-Person Healing
As Robert Brennan observed, psychology must be more than a fragmented science of parts—it must be the science of man as man, and the Thomistic framework offers precisely that. By restoring the soul—not as a mystical abstraction, but as the vital principle of life and unity, it integrates neuroscience with ethics, behaviorism with purpose, and cognition with meaning, reshaping along the way the goals and methods of clinical practice.
For instance, this approach allows therapy to address not only symptoms or behaviors, but also moral agency, conscience, and rational choice. From this perspective, disorders like addictions are understood not merely as neurochemical imbalances, but as manifestations of disordered desires and a weakened will. True healing, therefore, goes beyond symptom management—it requires the strengthening of the will and reorganization of emotions.
Moreover, this view makes room for transcendence. It acknowledges that human suffering often stems from loss of purpose, disconnection from ultimate ends, and interior fragmentation. A factor that cannot be ignored when it comes to understanding the underlying causes of many cases of substance abuse and addictive behaviors, not to mention other disorders.
Rediscovering the Whole Person
Modern psychology stands at a crossroads. It can continue down the path of fragmentation—treating the mind as a function, the body as a mechanism, and the soul as a myth. Or it can return to a richer tradition that views the human person as a unified substance, ordered toward truth, goodness, and ultimately, God.
The Aristotelian-Thomistic framework does not reject science; it contextualizes it within a broader metaphysical understanding. By affirming the substantial unity of body and soul, it allows psychology to be what it was always meant to be: the rational study of the whole human person. In recovering this vision, we not only solve the mind-body problem—we recover the very subject of psychology itself.
Nicolás Eyzaguirre Bäuerle
Editor-in-chief
