The homunculus argument is an informal fallacy whereby a concept is explained in terms of the concept itself, recursively, without first defining or explaining the original concept. This fallacy arises most commonly in the theory of vision. One may explain human vision by noting that light from the outside world forms an image on the retinas in the eyes and something (or someone) in the brain looks at these images as if they are images on a movie screen (this theory of vision is sometimes termed the theory of the Cartesian theater: it is most associated, nowadays, with the psychologist David Marr). The question arises as to the nature of this internal viewer. The assumption here is that there is a "little man" or "homunculus" inside the brain "looking at" the movie. The reason why this is a fallacy may be understood by asking how the homunculus "sees" the internal movie. The obvious answer is that there is another homunculus inside the first homunculus's "head" or "brain" looking at this "movie". But that raises the question of how this homunculus sees the "outside world". To answer that seems to require positing another homunculus inside this second...