Humans Have a Spiritual Nature

    We have shown that humans are physical.  Are they merely physical?  Are the physicalists correct that everything is entirely physical, including humans?  Is all knowledge therefore physical knowledge?  Can everything about humans be known in terms of matter, energy, and mathematical laws?  The key thought-experiment to consider is referred to as the knowledge argument, put into modern form by Frank Jackson.  We shift our focus here from physics to neuroscience, but the change in focus is not as great as it first appears because neuroscience (and all other science) is understood, as a fundamental principle of science, to completely reduce to physics.  Imagine Mary, who is born completely color blind. In all other ways her vision and experience are the same as any other human. As she grows up, she becomes interested in color, and becomes the world’s pre-eminent color scientist. She understands photons, rods, cones, and how given the signal on the red and the green cones, the brain measures the first axis of color information, and how given the signal on the blue and yellow (red plus green) cones, the brain measures the other axis of color information. She learns everything that physics and neuroscience can teach about color vision. Given any visual stimulus, she can experimentally determine what neurons fire in a given brain and measure what physical color information that person or animal acquires.

    After she has learned all the physical facts about color, medical science advances to the point that her visual defect is completely corrected, so that she can now see color. Now when she sees watered grass, she says, “Ah ha! So that is what it is like to see green.” When she sees a ripe tomato, she says, “Ah ha! So that is what it is like to see red.” She knew all physical facts before. She has learned a new fact: what it is like to see color. Therefore, there are facts in the universe which are not physical. We term these facts to be spiritual.  Modern philosophers use the term phenomenal.  I use spiritual here because I typically use the vocabulary of theologians throughout this web site, rather than philosophers.  Not coincidentally, these new facts are tied to consciousness. The conscious sensations of seeing colors, feeling pains, sensing warmth, etcetera are referred to as qualia (singular: quale).  Note that modern neuroscience has no place for consciousness, even though we all are aware of it.  This is the most important clue that neuroscience cannot tell us everything there is to know about being human.

    Let us look more deeply at the knowledge argument. What does it mean when we say that a fact is unknowable using physics? What we mean is that no matter how many textbooks Mary looks at and no matter how many conversations she has, she will not be able to learn what red looks like without experiencing it for herself. That is, what it is like to see red cannot be communicated with language (Benj Hellie, 'Inexpressible truths and the allure of the knowledge argument', in: There's Somethnig About Mary, pp 333-64). Physics is a mathematical language that describes nature, so it follows that anything that cannot be communicated with language cannot be communicated with physics.

    Let us make our description of physics as a language more precise. Extrapolating from information theory (originally developed for computer science, but now applied to many fields, including physics and neuroscience), any distribution of matter and energy can be represented as a series of bits (that is, zeros and ones), where the bits are information. In order to see how the bits propagate with time, it is necessary to have operations (add, shift, etcetera) which act on the bits. These operations are used to represent laws of physics. Essentially, a fact can be represented in the language of physics if and only if it can be represented with bits and operations. An ideal physicist can translate any measured distribution of matter and energy into bits, run these bits through the operations that represent the laws of physics, and translate the resulting bits into predictions about the probabilities that future measurements will return specified results.  It follows that any field that reduces to physics (neuroscience, computer science, etcetera) can also in principle be expressed in its entirety with bits and operations. Mary could never learn what it is like to see red by looking at bits and operations. She must experience redness for herself. The knowledge argument teaches us that the epistemic power of physics is limited, and it can never explain every known fact as the physicalists expect it to.

    Let us push the knowledge argument a bit further. Can an entirely physical brain know spiritual facts? No. A physical brain stores information in bits (spiking activity, individual neuronal characteristics, and neuronal connections), and processes the bits with operations (spiking neurons cause others to spike, which can cause those neurons to change their characteristics, connections, or cause them to spike). The physical world stores information in bits (distribution of matter and energy), and processes the bits with operations (the laws of physics). With the knowledge argument, we demonstrate that knowable spiritual facts exist and that physics (or any collection of bits and operations) cannot contain them. Because the physical brain only has the functional capabilities granted it by physics, it cannot contain spiritual facts either.

    Therefore, we must assert that the mind has both a physical and a spiritual nature.

This page was last changed on 2007/12/28