they argue that no epistemological position has priority in the acquisition of knowledge for there are always many ways in which to come to know the world. But this does not mean that all views are equally valid and they believe in the possibility of rationally adjudicating between competing knowledge claims. What is important to science is that any and every claim is open to challenge and, moreover, that all claims require epistemological support. This does not mean that these epistemological supports are always predicated on facts, or other such empirical data, but it does mean that those concerned to challenge particular claims make clear the evidential basis on which the challenge is made.