 The scientists’ relatively dismissive attitude towards alleged underdetermination threats may be based on a more demanding conception of empirical  success.[17]  Scientists demand much more of their theories than mere compatibility with some set of observational claims: they must fit into a larger explanatory scheme, and be compatible with other successful theories. Given a more stringent account of empirical success it is much more challenging to find rival theories. (We return to this issue in  §5  below.)