The experiment involves a woman, Mary, who is a brilliant scientist that is forced to investigate the world from a black and white room and a black and white television screen. Mary is a specialist in neurophysiology of vision and, we assume, that this enables her to obtain all of the physical information there is to obtain about what goes on when we see things in our everyday life, what seeing an apple feels like or what looking at the grass feels like. Mary's brain produces the same combination of wavelengths from that apple that stimulate the retina, as well as how this ends with her uttering, "The apple is red." Jackson asks us to then imagine what will happen to Mary if she is given a color monitor. Will she then learn new information? He states, "It seems obvious that she will learn something about the world and our visual experience of it." But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have then that, and Physicalism is false. .
I find this to be Jackson's strongest argument for his theory because it appears to successfully show that someone with all the physical information possible about an experience can fail to have all the information there is to have. It is missing the qualia or the property of experience and therefore false. Mary could know everything there is to know physically about the vision sense and how to react, but Mary learns something new when she experiences the color vision for herself. This qualitative experience adds knowledge or understanding to what she previously knew to be all true, so we must not be including something. The problem here is that Jackson argues that knowing all there is to know physically about something does not mean you know all there is to know, that there must be something more, without giving any reasonable explanation of what we are missing.