Whereas "good" reductionism means explaining a thing in terms of what it reduces to (for example, its parts and their interactions), greedy reductionism occurs when "in their eagerness for a bargain, in their zeal to explain too much too fast, scientists and philosophers ... underestimate the complexities, trying to skip whole layers or levels of theory in their rush to fasten everything securely and neatly to the foundation".
It is often said of this school of thought (which dominated the field of psychology, at least in the Anglo-American world, for part of the twentieth century) that it denied the existence of mental states such as beliefs, although at least in Skinner's original version it merely denied the theoretical utility (or necessity) of postulating such states in order to explain behavior.
As Dennett says, "Skinner proclaimed that one simple iteration of the fundamental Darwinian process—operant conditioning—could account for all mentality, all learning, not just in pigeons but in human beings.
Those nonreductive physicalists, such as Colin McGinn, who claim the true relationship between the physical and the mental may be beyond scientific understanding—and therefore a "mystery"—have been dubbed mysterians by Owen Flanagan.
The assertion is usually made in a slurring tone which implies that the brain has been overrated in some unspecified way and is supposed to put an end to further discussion.
One of its earliest documented uses was in a 1935 review by W. J. H. Sprott of Carl Jung's book Man in Search of a Soul in the journal Mind.