Trialism

Trialism is the theory of mind that posits reality as consisting of three fundamental substances or aspects, as opposed to the one of monism (e.g., materialism or idealism) or the two of dualism. There are two distinct kinds of trialism: a reinterpretation of René Descartes's dualism (implicitly in a religious context of the “soul”) and secular-philosophical three-part models of existence.

The more common trialism argues that in addition to Descartes’s mind (res cogitans) and body (res extensa), he implicitly or explicitly included a third, intermediate substance or faculty related to sensations, emotions, and the union of mind and body. The motivating idea is to resolve the difficulties of traditional mind-body dualism, namely the ‘interaction problem’—how an immaterial mind can possibly interact with a material body. By introducing a third element, trialism attempts to bridge this causal gap.

The three proposed substances are typically:

• Mind (or Intellect): The purely mental, thinking, non-extended, immaterial substance. This is the seat of consciousness, producing reason, self-awareness, and unalloyed thought.
• Body (or Matter): The purely physical, extended substance that is governed by the laws of physics and is non-mental.
• The Union of Mind and Body (or Sensation/Passion): A third, distinct category that is neither pure mind nor pure body, but a composite where the two are inextricably linked. This third ‘thing’ is responsible for sensory perceptions, emotions, appetites, and the phenomenal experience of being an embodied self.

Trialism’s critical, distinguishing point is that this third category is not merely an effect or combination or interaction of the other two; this union of mind and body is considered to have its own primitive, irreducible nature. Thus, in the trialist view, sensations like pain or feelings like joy are not just mental states about bodily states, nor are they just physical events. They are primitive, irreducible phenomena arising from the unique, substantial union of mind and body.

Cottingham’s Trialism

Philosopher John Cottingham argues that the standard dualist reading of Descartes is an oversimplification. He suggests that Descartes's later works, particularly his correspondence with Princess Elisabeth of Bohemia, reveal a more complex picture.

Elisabeth famously challenged Descartes on how an immaterial soul could move a material body, an argument that persists to this day. In his responses, Descartes introduced the idea of a “primitive notion” of the union of mind and body. Cottingham interprets this not just epistemologically but ontologically, referring to a genuine, third type of entity. “Thus we have, corresponding to the three 'primitive notions' of mind, body and the union, three distinct kinds of properties and three distinct kinds of explanation appropriate to them” (Cottingham, 1983).

For Cottingham, this third notion is not just a conceptual tool but points to the reality of psychophysical phenomena like sensation and passion. He argues that Descartes realized these could not be adequately explained by reducing them to either pure thought or pure mechanics. “The passions, for example, which Descartes analyses in his last published work, are for him prime examples of the operation of the mind-body union… Such modes of awareness are not, for Descartes, reducible to purely intellectual states of a disembodied mind, but are irreducibly psychophysical” (Cottingham, 2008).

Popper and Eccles’s Three Worlds

Philosopher Karl Popper, supported by neurophysiologist and Nobel Laureate John Eccles, proposed a different kind of trialism, a theory of three ‘worlds’:

• World 1: The world of physical objects and states.
• World 2: The world of subjective experiences and mental states (in particular, consciousness).
• World 3: The world of objective knowledge, including scientific theories, language, and art—the products of the human mind.

As Popper put it, “I propose to call the physical world 'World 1', the world of our conscious experiences 'World 2', and the world of the logical contents of books, libraries, computer memories, and suchlike 'World 3'” (Popper, 1972).

As Eccles put it, “I fully accept the recent philosophical achievements of Sir Karl Popper with his concept of three worlds. I was a dualist, now I am a trialist! Cartesian dualism has become unfashionable with many people. They embrace monism to escape the enigma of brain-mind interaction with its perplexing problems. But Sir Karl Popper and I are interactionists, and what is more, trialist interactionists!” (Eccles, 1973).

While the Popper-Eccles “Three Worlds” can be understandably seen as a form of dualism (Worlds 1 and 2), World 3, as an autonomous, objective realm (even though man-made), gives the model a triadic structure. The only way World 2 (consciousness) can interact with World 1 is via the medium of World 3 (concepts, theories, etc.), thus reifying World 3.

Penrose’s Three Worlds

Mathematician and Nobel Laureate Roger Penrose’s “three worlds” are three distinct but interconnected realms: the Physical World (the universe of material objects and physical laws), the Mathematical or Platonic World (the realm of abstract objects or forms, such as mathematical truths), and the Mental World (the domain of consciousness and subjective experience). He links the three worlds in his famous ‘impossible triangle,’ which portrays causal interactions between the worlds: the physical giving rise to consciousness, which in turn engages with the mathematical/Platonic.

According to Penrose, the three-world relationships have both symmetry and asymmetry:

• Instantiation: A small part of the Platonic/mathematical world relates to the physical world (the equations of physics).
• Generation: A small part of the physical world generates the mental world (the brain, with its sensory arrays and central processing).
• Comprehension: A small part of the mental world explores and interprets the Platonic (e.g., mathematical theorems).

Platonism/Neoplatonism

Platonic and Neoplatonic thought also contains trialistic elements, often envisioning a ‘World Soul’ or an intermediate realm of Forms that mediates between the ultimate, transcendent Good (or One) and the material world.

In short, trialism, in its various manifestations, offers an alternative to the classic mind-body debate. By introducing a third fundamental category—whether understood as a mind-body union, a world of objective knowledge, a capacity to comprehend, or some other kind of intermediary—it attempts to provide a more integrated and complete account of reality that includes conscious experience.

References

Cottingham, John. "Cartesian Trialism." Mind, vol. 94, no. 374, 1985, pp. 218–30.

Popper, Karl R., and John C. Eccles. The Self and Its Brain. Springer International, 1977.