Since 1915, 16 Australians have either shared a Nobel Peace Prize or won a Nobel outright. Of these prizes, half have been awarded in the category of “physiology or medicine.” One of them was awarded in 1963 to the neurophysiologist John C. Eccles (1903-1997), who had also just been named “Australian of the Year” by an Australian government organization. Eccles had already received a knighthood in 1958 and, today, the Eccles Institute of Neuroscience at the Australian National University is named in his honor.

Sir John graduated with first-class honors from medical school at the University of Melbourne, the city where he had been born and raised. However, puzzled during his medical studies by the nature of the interaction between mind and body, he then proceeded to earn a doctorate from Oxford University as a Rhodes scholar, specializing in neuroscience. Eventually, it was for his work on synapses and neurotransmission that he was awarded his Nobel.

Today, beyond the very specialized world of neurophysiology, Sir John Eccles is probably best remembered for his advocacy of the proposition that the mind and the physical brain are two quite different things. And his best-known contribution in that regard is a remarkable 1977 book titled — quite deliberately — “The Self and Its Brain,” co-authored with the famous Anglo-Austrian philosopher Sir Karl Popper (1902-1994). He revisited the topic more than once, including his 1994 book titled “How the Self Controls Its Brain.”

In “The Self and Its Brain,” as one neurologist put it in a 1978 review of the book, “two of the most remarkable figures of the 20th century have come together to defend ideas that many of their contemporaries would regard as outmoded. ... Popper and Eccles have adopted a philosophical posture that most modern philosophers and scientists would place in the same category as a belief in rain gods or special creation. ... This book cannot, however, be dismissed casually. The authors in fact take the stand that mind is real, with a separate existence from the body. Even more striking, they argue that mind is more than an ethereal corona surrounding a real electrical discharge, and that what goes on in the mind in turn influences the physical world. They believe, therefore, not merely in mind-body parallelism, but in actual interaction between the two. The combination of the talents of the two authors makes it difficult to reject the argument on the basis of either philosophical naïvete or ignorance of the workings of the real brain.”

Famously, Eccles and Popper distinguish between three “worlds” that, in their view, make up the whole of reality.

“World 1,” as they call it, is the realm of physical objects and states, the whole cosmos of matter and energy and biology (including human brains). The paper and ink of books are part of “World 1,” but not the ideas they contain. “World 1 is the total world of the materialists. They recognise nothing else. All else is fantasy.”

“World 2” is the sphere of states of consciousness, of subjective knowledge and perceptions such as light and color, sound, music and harmony, touch, smells, flavors and the like. “These qualities do not exist in World 1, where correspondingly there are but electromagnetic waves, pressure waves in the atmosphere, material objects, and chemical substances.” World 2, say Eccles and Popper, “is our primary reality.” (The fact that consistent materialism tends to reject it as fantasy, in their judgment, says far more about materialism than about reality.)

Finally, “World 3” is the world of culture, created by humans and, in turn, shaping humans. “World 3 is the world that uniquely relates to man. It is the world which is completely unknown to animals. They are blind to all of World 3.”

The dominant viewpoint among many scientists and others today, as it has been for many years, is “monism” or “reductionism,” which holds that there is only one mental reality: Mind is reducible to brain; when the brain is dormant or destroyed, consciousness ceases. Of course, nobody doubts the undeniable fact that mind and brain are closely related, that serious brain damage and many drugs affect mental function. Eccles, however, was a deeply thoughtful, learned and unembarrassed defender of what he and Popper called “dualist interactionism.” On this view, mind and brain are mutually intertwined but distinct. Our minds cannot simply be reduced to our material brains.

Daniel Peterson founded the Middle Eastern Texts Initiative, chairs The Interpreter Foundation and blogs on Patheos. William Hamblin is the author of several books on premodern history. They speak only for themselves.