An Overview of the Monism-Dualism Debate on Human Composition

For two thousand years Christians of all stripes (clergy and laypersons, scholars and uneducated, young and old, and across denominations) have traditionally understood human beings to be composed of two substances: a physical body and a spiritual soul. While some have argued that the non-physical substance includes two different kinds of non-body parts (i.e., a soul and a separate spirit), the point is that humans have been understood as consisting of a physical body on one hand and some non-physical something on the other. This two-fold understanding of human composition is sometimes referred to as “substance dualism.”

But recently a number of different challenges to substance dualism have been articulated by scholars in various academic disciplines. Questions have arisen in the historical and theological disciplines. Biblical scholars have observed that terms like “soul” and “spirit” have flexible uses in the Bible and sometimes refer simply the whole person and not parts of persons. Theologians note that in the Bible, especially the Old Testament, God seems to deal with humans in a more holistic way, and certainly theology affects the whole person. Historians have suggested that dualistic thinking about human composition entered Christian thinking from Greek philosophy and not from Scripture.

Questions have also been raised in the philosophical disciplines. Metaphysicians suggest that the notion of a non-physical substance seems rather incoherent, and even if granted, the ability for the immaterial to interact with the material (presumed by dualistic views) seems untenable. Ethicists note that dualistic thinking has had negative impacts in that the soul has been over-emphasized and the body undervalued to the point of neglect and/or abuse. Others propose that dualism seems unnecessarily complex for understanding human existence since the complexities of human existence seem to be adequately accounted for by “levels” of experience rather than some completely other substance.

Most recently, questions have been raised in the scientific disciplines. In the expanding research of neuroscientists, experiments seem to indicate that consciousness is entirely a physical occurrence (as is the thing that has consciousness, i.e., the physical brain), and that mental states are dependent upon particular brain states. For psychologists, the human being seems to have every experience, including emotions, in the body; and even “out-of-body” experiences are reported with references to physicality.

While versions of these kinds of questions about substance dualism have been around for a long time, the last few decades have seen a rise in such concerns in thinking about the body–soul question (a.k.a. the mind–body problem). So much so that philosophers, scientists, and theologians have been proposing monistic views of human composition over against substance dualism. That is, more and more scholars—including Christian thinkers in these disciplines—are suggesting that humans are not composed of two substances (physical and non-physical) but of one substance (physical).

Now, to be clear, there are not just two options here, substance dualism or monism. Rather, there are a variety of dualistic views and a variety of monistic views about what human persons are. We can place the variety of views about human composition on a left-to-right continuum with the strongest monistic views on one end and the strongest dualistic views on the other end. Here is a sketch of such a continuum that identifies eight different explanations of the body–soul question (acknowledging that there are other more nuanced positions between those marked here).

For those interested in investigating book-length treatments on these positions, here are prime examples of each of the eight views:

1. Reductive Materialism: Francis H. Crick, The Astonishing Hypothesis: The Scientific Search for the Soul (New York: Simon & Schuster, 1994).
2. Nonreductive Physicalism: Nancey Murphy, Bodies and Souls, or Spirited Bodies? (Current Issues in Theology; New York: Cambridge University Press, 2006).
3. Constitution View: Kevin J. Corcoran, Rethinking Human Nature: A Christian Materialist Alternative to the Soul  (Grand Rapids: Baker, 2006).
4. Emergent Dualism: William Hasker, The Emergent Self (Ithaca, NY: Cornell University Press, 1999).
5. Holistic Dualism: John W. Cooper, Body, Soul & Life Everlasting: Biblical Anthropology and the Monism-Dualism Debate (rev. ed.; Grand Rapids: Eerdmans, 2000).
6. Substance Dualism: J. P. Moreland and Scott B. Rae, Body and Soul: Human Nature and the Crisis in Ethics (Downers Grove: InterVarsity Press, 2000).
7. Radical Dualism: Sir John Eccles and Daniel N. Robinson, The Wonder of Being Human: Our Brain and Our Mind (New York: Free Press, 1984).
8. Idealism: Keith Ward, More than Matter? Is There More to Life Than Molecules? (Grand Rapids: Eerdmans, 2011). We can note here that idealism is a monistic view that stresses the non-physical rather than the physical. Thus, at idealism our continuum curves back on itself into a circle with position eight standing next to position 1.

A single volume with exposure to four different views on this subject (views in the middle of the continuum) is Joel B. Green and Stuart L. Palmer, eds., In Search of the Soul: Four Views of the Mind-Body Problem (Downers Grove: InterVarsity Press, 2005; 2^nd ed., Eugene, OR: Wipf & Stock, 2010). Green and Palmer edit this multiple-view book for the interaction of advocates of different views on human composition: Stewart Goetz on “substance dualism,” William Hasker on “emergent dualism,” Nancey Murphy on “nonreductive physicalism,” and Kevin Corcoran on “the constitution view.”

So, even after investigating some the scholarly interaction, how do we move forward in this discussion? Do the questions and challenges put forward against substance dualism (as outlined above) fatally threaten the historic Christian understanding of human composition? Should the focus of Christian theology move on the continuum away from substance dualism? And if so, where should it move? Or should the Christian understanding of human persons broaden to include several different views? And how is any of this discussion practically helpful anyway? For most Christian believers, these kinds of questions should be approached primarily through the lens of Scripture.