The delimitation between science and pseudoscience is part of the more general task of determining which beliefs are epistemologically justified. Standards for demarcation may vary by domain, but several basic principles are universally accepted. Karl Popper proposed falsifiability as an important criterion in distinguishing between science and pseudoscience. He argues that verification and confirmation can play no role in formulating a satisfactory criterion of demarcation. Instead, it proposes that scientific theories be distinguished from non-scientific theories by testable claims that future observations might reveal to be false.