text: **Knowledge argument**
  
  The knowledge argument, also known as*Mary's Room*, is another common thought experiment: A 
  hypothetical neuroscientist named Mary has lived her whole life in a black-and-white room and has never 
  seen colour before. She also happens to know everything there is to know about the brain and colour 
  perception.[50] Chalmers believes[48] that when Mary sees the colour red for the first time, she gains new 
  knowledge — the knowledge of "what red looks like" — which is distinct from, and irreducible to, her 
  prior physical knowledge of the brain or visual system. A stronger form of the knowledge argument[50] 
  claims not merely that Mary would lack subjective*knowledge*of "what red looks like," but that she 
  would lack knowledge of an objective*fact*about the world: namely, "what red looks like," a non-physical 
  fact that can be learned only through direct experience (qualia). Others, such as Thomas Nagel, take a 
  "physicalist" position, disagree with the argument in its stronger and/or weaker forms.[50] For example, 
  Nagel put forward a "speculative proposal" of devising a language that could "explain to a person blind 
  from birth what it is like to see."[31] The knowledge argument implies that such a language could not 
  exist. 