 More recent work on the issue of simplicity has borrowed tools from statistics as well as from probability theory. It should be noted that the literature on this topic tends to use the terms ‘simplicity’ and ‘parsimony’ more-or-less interchangeably (see Sober 2003). But, whichever term is preferred, there is general agreement among those working in this area that simplicity is to be cashed out in terms of the number of free (or ‘adjustable’) parameters of competing hypotheses. Thus the focus here is totally at the level of theory. Philosophers who have made important contributions to this approach include Forster and Sober (1994) and Lange (1995).