In philosophy of mind, Mary’s Room is a thought experiment meant to demonstrate the non-physical nature of mental states. It is an example meant to highlight the knowledge argument against physicalism. The example first appears in an article by Frank Jackson, entitled “Epiphenomenal Qualia”, which appears in Philosophical Quarterly 32:127 (1982).
The thought experiment is as follows: Mary lives her entire life in a room devoid of colour—she has never directly experienced colour in her entire life, though she is capable of it. Through black-and-white books and other media, she is educated on neuroscience to the point where she becomes an expert on the subject. Mary learns everything there is to know about the perception of colour in the brain, as well as the physical facts about how light works in order to create the different colour wavelengths. It can be said that Mary is aware of all physical facts about colour and colour perception.
After Mary’s studies on colour perception in the brain are complete, she exits the room and experiences, for the very first time, direct colour perception. She sees the colour red for the very first time, and learns something new about it — namely, what red looks like.
Jackson concluded that if physicalism is true, Mary ought to have gained total knowledge about colour perception by examining the physical world. But since there is something she learns when she leaves the room, then physicalism must be false. As Jackson explains:
It seems just obvious that she will learn something about the world and our visual experience of it. But then is it inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false.
The Mary’s Room example has been cited by a number of other philosophers, such as David Chalmers who uses the example to suppose that there are additional irreducible properties of the brain beyond the physical ones known to scientists.
It is important to note, though, that years later, Jackson reversed his stance on the argument, explaining that the knowledge argument and Mary’s Room are deeply rooted in our intuitions about the matter, but that science can offer other explanations for the apparent discrepancy.