 Reductivists are generally realists about the reduced phenomena and their views are in that respect conservative. They are committed to the reality of the reducing base and thus to the reality of whatever reduces to that base. If thoughts reduce to brain states and brain states are real, then so too are thoughts. Though conservative realism is the norm, some reductionists take a more anti-realist view. In such cases the reducing phenomena are taken to replace the prior phenomena which are in turn eliminated. The idea of mental illness as a type of psycho-neural disorder replaces the idea of demon possession. Demons and their voices have no role or reality in the new theory. The oxygen theory of combustion replaced the phlogiston theory and phlogiston was eliminated.