Full Idea
Mary knows all the physical facts. ..It seems, however, that Mary does not know all there is to know. For when she is let out of the black and white room .. she will learn what it is like to see something red.
Gist of Idea
Mary knows all the physical facts of seeing red, but experiencing it is new knowledge
Source
Frank Jackson (What Mary Didn't Know [1986], §1.4)
Book Reference
Perry,John: 'Knowledge, Possibility and Consciousness' [MIT 2001], p.15
A Reaction
Jackson is begging the question. A new physical event occurs when the red wavelength stimulates Mary's visual cortex for the first time. For an empiricist raw experience creates knowledge, so it can't BE knowledge. Does Mary acquire a new concept?