Qualia are the subjective experience of sensory stimuli. The redness of red. The smell of a rose. The taste of coffee. The pain of a headache. Qualia are private. They cannot be fully communicated. You can describe red to a blind person. They will never know what red looks like. That is the qualia problem.

The term comes from the Latin qualis, meaning of what kind. Philosophers debate whether qualia exist. Some say they are real and irreducible. They cannot be explained by physical processes. Others say they are illusions. They are just brain states. The debate is central to the philosophy of mind. It is the hard problem of consciousness.

Examples of qualia

• The redness of a rose.
• The taste of chocolate.
• The sound of a violin.
• The feeling of pain.
• The smell of rain on dry pavement.

Qualia are what make consciousness mysterious. A neuroscientist can map the brain activity associated with seeing red. But they cannot explain why it feels like red. The feeling is extra. It is not captured by the physics. That is the explanatory gap. Some philosophers argue that qualia do not exist. They are just words we use to describe brain states. Others argue that qualia are the most real thing there is. They are the only thing we know directly. Everything else is inference. Qualia are the given. They are the starting point of experience. Without them, there is no experience. There is just information processing. The debate continues. Qualia are private. They are ineffable. They are the inner life of the mind. They are what it is like to be you.