I have recently been watching the fascinating iTunes lectures by Tamar Gendler on the philosophy of human nature. Two of the lectures discuss what she terms "parts of the soul", but what I will here rather cumbersomely refer to as "parts of human personhood". Reviewing the western tradition, Gendler traces our tendency to subdivide the human person into parts to a continuous tradition in western philosophy and psychology. She discusses, amongst others, Plato's distinction between appetite, ratio and spirit, Freud's division between id, ego and superego, and more recently, the immensely popular division in cognitive psychology between system 1 (phylogenetically old, unconscious, and fast) and system 2 (more philogenetically novel, under conscious control and slow).
Such divisions of human personhood are cross-culturally ubiquitous...
The Egyptians had a complex distinction between several mental parts (e.g., Ren, Ba, Ka, Sheut, and Ib) and parts of the human body. Chinese philosophy and folk psychology distinguish, amongst other things, the mind (heart) and life force (chi). This culturally widespread tendency suggests that distinguishing parts of personhood might be the spontaneous outputs of universal cognitive processes. We are not intuitive monists. What features of human cognition can explain our tendency to divide non-physical aspects of human personhood? And what are the parts that we intuitively distinguish? These two questions turn out to be surprisingly hard to address, but I believe their answers are fundamentally related.
One influential attempt, coming from Paul Bloom (e.g., 2005), holds that humans are Cartesian mind-body dualists. Bloom proposes that this tendency is due to the existence of two distinct ways of reasoning about the physical and the mental. We use very different inferences when we want to explain someone's behavior through internal mental states (beliefs, desires), than when we want to explain purely physical states of affairs like one ball colliding with another ball. Thus, it becomes quite intuitive and natural to continue to imagine a deceased person's mental states as existing in a separate dimension, even when that person is no longer able to physically act. Bloom reasoned that all children are intuitive Cartesian dualists: they think of the mind as an aphysical entity, distinct from the physical body. One problem with this picture, as Hodge (2008) pointed out, is that Cartesian dualism is a relatively rare view. Descartes held it, of course, but the folk religious beliefs we see around us are much more complex. To complicate matters further, some religions (such as Christianity and Islam) do not envisage life after death in a disembodied state, but as very much a resurrection of body and mind. Hodge proposed that our intuitive personhood is tripartite: mind, body, and soul.
Richert and Harris (2008) also make this tripartite distinction (body, mind and soul). They propose that the concept of soul develops in young children independently of the concept of mind. The mind is regarded as more cognitive, whereas the soul is regarded as associated with spiritual functions. The picture gets further complicated, however, as intuitive belief in a life force or vital energy may be distinct from the concepts of soul, mind and body (see Inagaki & Hatano 2004). Life force is a non-mental causal force that accounts for biological health and well-being (Roazzi et al 2013). The concept is pervasive in Eastern philosophies and religion (e.g., the concept of chi), but seems to be present in young children cross-culturally. The health bar in computer games, which can get depleted or replenished as one gets injured or receives nourishment, provides a nice illustration. It indicates that even for westerners who do not have life force in their ontology, it is intuitive to reason with this concept.
Perhaps our intuitive conceptualization of the mental can be further subdivided into intuitive inferences about the intellect on the one hand, and inferences about desires and emotions on the other. The tendency to see the ratio as a separate faculty, independent from emotions, is indeed quite widespread. We find it not only in Plato's distinction between ratio, appetite and spirit, Hume's distinction between reason, the passions, and will, or in Freud's ego, id and superego, but also, e.g., in Jainism, where one has the obligation to avoid harming others, but especially to harm those with senses, such as animals, and those with ratio, such as humans. Remarkably, Winer et al (2009) found that young children (first-graders) are more likely to see the heart as the locus of emotions, such as happiness and sadness, whereas they regard cognitive processes (e.g., remembering facts) as located in the brain. This tendency decreases as children get older, with an increasing tendency to locate all mental processes in the brain.
I think that the final picture of our intuitive conceptualization of human personhood will be quite nuanced and complex, with finer subdivisions than currently suggested in the literature (e.g., Bloom's body-mind dualism or Richert and Harris' body-mind-soul tripartition). Why are humans not intuitive monists? Why do we continue to grant a separate ontological status to parts of the person, in spite of the influence of methodologically naturalistic and physicalistic views on personhood (e.g., cognitive neuroscience)?
One way to explain this pervasive tendency is to take an evolutionary perspective. Other humans were, of course, of vital importance in our evolutionary history. To act adaptively, our inferences about them would have to be quite fine-grained. Such inferences could include keeping track of someone's health (using the concept of life force as a heuristic), their tendency to be influenced by desires and emotions (Plato's appetite; Hume's passions, system 1, etc), their ability to make inferences, memory and other cognitive capacities (ratio, system 2, etc). Such fine-grained inferences would be useful: for instance, keeping in mind that someone is not very clever (appealing to an intuitive concept of ratio) might be useful in direct and indirect social interactions.
Ideally, such an evolutionary picture should be supported by rich anthropological and psychological data, documenting how people reason about the mental in diverse cultures, as I expect beliefs about non-physical personhood will be affected by societal and other cognitive attractors (e.g., ways of organizing social relationships). But I expect this sort of more systematic investigation will reveal that we are not intuitive Cartesian dualists — nor do we have a straightforward distinction between body, soul and mind.
Bloom, P. (2005). Descartes' baby: How the science of child development explains what makes us human. Vintage.
Hodge, K. M. (2008). Descartes' mistake: How afterlife beliefs challenge the assumption that humans are intuitive Cartesian substance dualists. Journal of Cognition and Culture, 8(3-4), 3-4.
Inagaki, K., & Hatano, G. (2004). Vitalistic causality in young children's naive biology. Trends in cognitive sciences, 8(8), 356-362.
Richert, R. A., & Harris, P. L. (2008). Dualism revisited: Body vs. mind vs. soul. Journal of Cognition and Culture, 8(1-2), 1-2.
Roazzi, M., Nyhof, M., & Johnson, C. (2013). Mind, Soul and Spirit: Conceptions of Immaterial Identity in Different Cultures. International Journal for the Psychology of Religion, 23(1), 75-86.
Winer, G. A., Cottrell, J. E., & Bica, L. A. (2009). When hearts, hands, and feet trump brains: Centralist versus peripheralist responses in children and adults. British Journal of Developmental Psychology, 27(2), 343-364.