The causes of our beliefs are multifarious. For some beliefs held by some people at some time, there may well be good reasons. This is a quite weak claim; anything stronger would require an epidemiological investigation into the occurrence of rational belief, or knowledge. However, in explaining why some scientist came to hold the beliefs they did, we can rightly appeal to principles of logic, epistemology and methodology (the structure of these explanations can be found in sections 5.4 and 6.1). However it would be wrong to make the strong claim that for all explanations of all scientific beliefs held by all people at all time, some rationality model is applicable. On the contrary, there are multifarious ways in which people can come to accept, or believe or entertain some proposition. As has been argued, claims about knowledge must be intrinsically rationally based, otherwise they cannot be knowledge. Knowledge is a normative critical notion. However it must be allowed that what one person holds as an item of knowledge, another will hold simply as a belief, often on grounds that have little to do with normativity.