William S. Robinsoncounterintuitive, and Jackson is no longer content to accept it. In a 1996 book (with David
Braddon-Mitchell) he defended the Knowledge Argument against several replies in criticism
of it. He did not claim to see exactly why it failed, but offered the “There must be a reply”
reply to it. That is, he thought that there must be something wrong with the argument, even
if we cannot explain what the error is. Naturally, advocates of the Knowledge Argument find
this stance unsatisfying. “There must be a solution to a problem for my account (even though
I can’t think of one)” is not generally accepted as an adequate defense of views in philosophy
or in science.
A sixth kind of argument turns on the Relative Simplicity of properties in our sensations.
To understand this argument, we may begin with a less dramatic version of Jackson’s starting
point. Consider that congenitally blind people usually know many things about colors, and
some know a great deal about light waves, stimulation of retinal cells by light, optic nerves, and
visual processing in the brain. Yet it is extremely plausible that something is missing from their
experience. They may know that a red light means one should stop, but they have never had the
experience that gives “red” its meaning, in normally sighted people. Advising them to repair this
lack by studying harder would be an exercise in grim humor.
These remarks can be generalized to apply to congenitally deaf people, who may know about
compression waves in the air; and to people who know about molecular structures of molecules
they are unable to smell, even though those molecules cause distinctive odor experiences in
most people. A few people are born without the ability to experience pain, but that does not
affect their intelligence, or their ability to understand anatomy.
The properties to which these considerations apply – colors, sound qualities, scents, flavors,
pains and others – are collectively known as phenomenal qualities or qualia. (The latter is pro-
nounced ‘kwah ́-lee-uh’ and its singular form is “quale,” pronounced ‘kwah ́-lay’.) Qualia are
properties, and they are the most intuitive candidates for non-physical properties.
Many qualia have some degree of complexity. For example, some sounds are chords, most
colors are mixtures (orange, for example, is a mixture of red and yellow), and cooks are often
complimented for the complexity of the tastes of their food. Qualia do not, however, have the
same degree of complexity as the physical properties with which they are correlated. For exam-
ple, they are not as complex as properties of compression waves, or patterns of light energies at
various wavelengths, or arrangements of bonding among atoms. Neither are qualia as complex
as the multitude of neural events that are required for us to have experiences.
This difference of complexity gives rise to the Relative Simplicity argument for a dualism of
properties (i.e., either property dualism or event dualism).
RS1. The physical properties with which qualia are correlated are complex.
RS2. Qualia are relatively simple properties (i.e., they are simple relative to their physical cor-
related properties).
RS3. No property can be both complex and relatively simple (i.e., no property can be simpler
than itself ).
So,
RS4. Qualia are not identical with their physical correlated properties.
RS5. Qualia are not identical with physical properties with which they are not at least
correlated.
So,
RS6. Qualia are not identical with any physical properties.