Qualia
quale · phenomenal properties
The felt qualities of experience — the particular redness of red, the specific character of a pain — and the part of the mind that physical description seems least able to capture.
In practice
Two people can agree on every measurable fact about a color and still have no way to check that their experience of it matches. Nothing observable distinguishes the cases.
The common mistake
Treating qualia as obviously real and obviously mysterious. That experiences have a character is agreed by everyone; whether that character is something beyond the physical story is the actual dispute.
Qualia are what experiences are like from the inside. The singular is quale. Seeing a ripe tomato involves a visual state with a particular character, and that character is what the word names.
Why they are a problem
Every other property science explains gets analyzed into structure and function: what a thing is made of, how it is arranged, what it does. Qualia appear to resist that, because a complete functional account of color vision seems to leave the question of why it looks like anything untouched. This is the core of the hard problem.
The two arguments
The knowledge argument. Frank Jackson's 1982 thought experiment imagines a scientist who knows every physical fact about color vision but has only ever seen black and white. On leaving the room and seeing red for the first time, does she learn something new? If she does, there was a fact she did not have, and physical facts are not all the facts.
The inverted spectrum. Suppose your experience of red is what mine is of green, consistently, throughout. Every behavioral and functional test would come out identical, because we both stop at the same lights and use the same words. If that is coherent, qualia are not fixed by function.
The replies
Physicalists respond in several ways. The scientist gains an ability rather than a fact — knowing how to recognize red rather than knowing a new truth. Or she learns an old fact in a new way, as someone can know that water is present without knowing it as H2O. Daniel Dennett argues the concept is confused and dissolves under examination, and that the intuitions supporting it come from the thought experiments rather than from anything observed.
Why it stays open
Nobody disputes that experiences have a character. The dispute is whether that character is something over and above the physical and functional story, and both sides agree no experiment settles it — which is itself the interesting fact about the problem. See mind-body problem and materialism.
Concept web
Open the full webQuestions
What are qualia?
The felt qualities of conscious experience — the particular way red looks or a pain feels. They are the aspect of mind that functional and physical description seems least able to capture.
What is the knowledge argument?
Frank Jackson's thought experiment about a scientist who knows every physical fact about color but has never seen it. If she learns something on first seeing red, physical facts are not all the facts.
Do qualia prove physicalism is false?
Physicalists have replies: the scientist gains an ability rather than a fact, or learns an old fact in a new way. Some argue the concept dissolves under examination. No experiment settles it.