Popper's supporters argued that most criticism is based on an incomprehensible interpretation of his ideas. They argue that Popper should not be interpreted as meaning that falsifiability is a sufficient condition for the demarcation of science. Some passages seem to suggest that he considers it is only a necessary condition. Other passages would suggest that for a theory to be scientific, Popper requires (besides falsifiability) other tests, and that negative test results are accepted. A demarcation criterion based on falsifiability that includes these elements will avoid the most obvious counter-arguments of a criterion based on falsifiability alone.