Research on purpose is aimed at identifying the perceptual variables that a system is controlling when it is carrying out various purposeful behaviors. The basic methodology used to do this kind of research is the test for controlled variable or TCV, which involves testing hypotheses about the perceptual variables the organism is controlling. These hypotheses are formal definitions of the perception under control. They are tested by looking for lack of an expected effect of disturbances to the hypothesized controlled variable. The TCV has to start with the formulation of hypotheses about the variables around which behavior is organized. The researcher has to be able to look at what an organism is doing and come up with definitions of the variables it is controlling – definitions that are precise enough so that it is possible to predict how disturbances would affect these variables if they were not being controlled.