what it is like

From Key Terms in Philosophy of Mind (Continuum, 2010):

what it is like, a phrase often used in philosophy of mind for discussing phenomenal character or QUALIA. Such uses include “What it is like to taste a lemon is more like tasting a lime than tasting chocolate” and “A person blind from birth does not know what it is like to see red.” Perhaps one of the most famous uses of the phrase is due to Thomas Nagel’s essay “What Is It Like to Be a Bat?” the titular question of which served to launch Nagel’s criticisms of the completeness of physical, objective science. See PHYSICALISM; OBJECTIVITY; SUBJECTIVITY. A line of thought against physicalism hinging on what it is like, similar to Nagel’s, was developed by Frank Jackson and others in terms of the now famous KNOWLEDGE ARGUMENT concerning conditions under which one may acquire KNOWLEDGE of what it is like to see red. Central to the knowledge argument is a THOUGHT EXPERIMENT concerning Mary, a hypothetical super-neuroscientist who knows all of the objective physical facts about human color vision but has never herself seen red before. Many philosophers share the INTUITION that Mary does not know what it is like to see red if all she has is knowledge of physical facts and has not herself seen red. The intuition that one could not know what it is like to have certain kinds of EXPERIENCE (e.g., tasting wine or pineapple) without first undergoing an experience of such a kind was appealed to by John LOCKE and David HUME in their arguments for EMPIRICISM. See also MOLYNEUX QUESTION; MISSING SHADE OF BLUE.