 Defenders of Popper have claimed that this criticism relies on an uncharitable interpretation of his ideas. They claim that he should not be interpreted as meaning that falsifiability is a sufficient condition for demarcating science. Some passages seem to suggest that he takes it as only a necessary condition (Feleppa 1990, 142). Other passages suggest that for a theory to be scientific, Popper requires (in addition to falsifiability) that energetic attempts are made to put the theory to test and that negative outcomes of the tests are accepted (Cioffi 1985, 14–16). A falsification-based demarcation criterion that includes these elements will avoid the most obvious counter-arguments to a criterion based on falsifiability alone.