The problem is that, in many cases for many systems, there may simply be no such thing as a truely independent variable. Out here in the real world, the phrase "independent" may often be oxymoronic. The very notion of independence reflects the world of Platonic idealism, a pure world populated by seperate discrete things each with its essensce, floating suspended in a sea of laws, rules governing the relations between these autonomous entities.
nontriviality of nonlinear dynamics in psychology of learning
doctoral dissertation, university of minnesota,