 To summarize, the main problem with a priori justifications of simplicity principles is that it can be difficult to distinguish between an a priori defense and no defense(!). Sometimes the theoretical virtue of simplicity is invoked as a primitive, self-evident proposition that cannot be further justified or elaborated upon. (One example is the beginning of Goodman and Quine’s 1947 paper, where they state that their refusal to admit abstract objects into their ontology is “based on a philosophical intuition that cannot be justified by appeal to anything more ultimate.”) (Goodman &amp; Quine 1947, p. 174). It is unclear where leverage for persuading skeptics of the validity of such principles can come from, especially if the grounds provided are not themselves to beg further questions. Misgivings of this sort have led to a shift away from justifications rooted in ‘first philosophy’ towards approaches which engage to a greater degree with the details of actual practice, both scientific and statistical. These other approaches will be discussed in the next two sections.