Welcome to the Century of Neuroscience, the Century of the Brain – Part I: Traditional Dualistic Views of Human Nature

Who am I? What is the nature of human nature? Of human persons? Such fundamental questions have been raised and debated from time immemorial. A host of answers have been given, and in this series of articles we will briefly survey the main categories of views. The traditional dualistic (two component) views will be considered in this article, with the trending monistic (one component) views introduced in the second article. In the third article, we will consider the working assumption of modern neuroscience, since neuroscience has relevance to how we view human nature. Here, the traditional dualistic views are briefly surveyed.

Two broad categories of views have dominated thinking about what constitutes human nature: dualism and monism. Dualism posits that humans are made up of two substances: matter (constituting the physical body) and soul (which is a non-material, non-discretely localized substance that functions as a controlling or governing agency or vital principle with respect to the material body).¹ Monism (also called physicalism or materialism), on the other hand, is the idea that humans are made up of just one substance: physical matter.

Within these two main categories are various permutations on the dualistic and monistic themes. Substance dualism is usually traced back to Plato. Plato distinguished between the Forms/ Universals/Ideas and the Particulars/Individuals/Matter (material objects). The human soul was precedent to and a superior aspect of the more spiritual realm of the Forms, and as such was quite separate and distinct from the inferior matter of the physical realm that was exemplified in the Particulars of material things, such as our physical bodies.

Plato’s intellectual descendants included the neo-Platonists, among whom were many Church Fathers, especially Augustine. These neo-Platonists developed variations of Plato’s dualistic ideas, integrating Platonic philosophy with Christian theology to generate early Christian anthropological views. In addition to illuminating human nature, these variations were important with respect to a number of early heresies, especially those contesting the orthodox view regarding the constitution of Christ’s human/divine nature. Ultimately, such heresies resulted in foundational early Church creeds/confessions. A common criticism of substance dualism has been its propensity to denigrate the body’s value, since it tends to maintain that the soul is the real you – a good-inclined personal essence trapped in an evil-inclined body – and needs to be liberated from its bodily prison (cf. Gnosticism).

Centuries later, but still influenced by the Platonic tradition, René Descartes advanced a substance dualistic view with respect to the mind: this view is now well-known as “Cartesian dualism.” Even before Descartes, mind and soul were closely related, if not somewhat interchangeable terms. In his time, however, Descartes felt compelled to argue for a distinction between mind and matter. He was able to conceive of how physical –  and especially hydraulic, mechanical – principles could potentially explain most of the capabilities and faculties of animals and humans. Unfortunately, given the nominal brain science of his day, it was difficult for him to conceive how higher and seemingly ineffable faculties such as human rationality could be explained by physical matter alone. Hence, he invoked the immaterial mind as a separate substance, quite distinct from, but somehow interacting with, the matter/substance of the physical body to produce cognitive abilities. How exactly such dissimilar substances as the immaterial, non-extended human mind and the physical matter of the human body could interact was a conundrum for Descartes and subsequent philosophers, and combining these two concepts continues to represent a major challenge for substance dualism.

Another challenge comes from Darwinian macroevolution. Non-human animals have traditionally been viewed as lacking souls, though they have at least rudimentary (and sometimes apparently fairly sophisticated) minds/mental capabilities. If one accepts macroevolution, one is challenged to answer the question of when the soul entered the lineage of the human species and how one might account for its appearance; indeed, how could non-material soul arise by evolution from a substance as distinctly different as matter?

Another major type of dualism comes through the intellectual line of Aristotle and the great scholastic philosopher, Thomas Aquinas, who attempted to integrate Aristotelian thinking with Christian theology. Aristotle’s dualism saw the soul as capable of existing independently of the body, but the soul is usually incomplete without a body. The normal situation in this life is a highly integrated soul-body complex, with the active soul acting as the form and actuating principle of the body’s passive matter (hylomorphism); the soul animates the body, thus creating the living psychosomatic unity we experience as “ourselves.” The two parts are completely integrated in this temporal life, like the components of a baked cake, but in the afterlife the soul and the body can be separated by God (according to Aquinas) and the soul re-integrated with a resurrection body.

Modern adherents refer to views such as this as “Thomistic dualism” or “holistic dualism” or (more recently, in a reverse of the emphasis) “dualistic holism.” Nuanced in various ways, they also go by names such as “property dualism,” “emergent dualism,” etc. Some version of these more Thomistic or dualistic holisms is preferred over substance dualism among most modern dualists. Still, dualistic holism faces some of the same (somewhat mitigated) challenges as substance dualism.

Aquinas is especially known for his conceptual dissection of the Aristotelian soul into the rich taxonomy of faculties which characterize humans (essentially representing the soul’s job description). As the result of modern neuroscience, the faculties/functions originally attributed to the Thomistic soul are now largely seen to be faculties/functions of brain matter, and this trend is continuing apace. To many, it appears that the soul’s job description is being greatly reduced.

For Christians through history until the 20^th century, some form of dualism has been the traditional and predominant view. Though the early Church fathers were not monolithically dualistic, dualism was the most common interpretation of the New Testament view, and the view was naturally adopted, since it was the Hellenistic philosophical milieu (due to Platonic and Aristotelian influence) at the time of Christ and for many subsequent centuries. More recently, in light of what revised biblical scholarship and modern neuro- and other related sciences are revealing, it has been argued that the dualism of these early centuries is an archaism of ancient pagan pre-scientific philosophical views and that it can be graciously disregarded as anachronistic (like Ptolemaic geocentricism, the 3-tiered heavens, etc.).

In the second installment of this article series, we will briefly survey Christian monism. Christian monists argue for a nuanced view of monism, which they believe: (1) is consistent with the central doctrines/teachings of orthodox Christianity, (2) takes discoveries in the neurosciences more seriously than dualism does, and (3) avoids the extreme reductionism often embraced by non-theistic monism.

1. In philosophy, a common definition of the term “substance” is that which is a cause of itself, can be conceived through itself and needs only itself to exist. ↩