 At its core, phylogenetic inference is about evaluating competing hypotheses. In an important sense, phylogeneticists are faced with what philosophers of science would identify as a problem of  underdetermination of theory by evidence . Multiple competing phylogenetic trees can explain the same data, though in conflicting ways; it is the phylogeneticists task to identify which of those hypotheses best explains those data. It will be useful to separate the problem into two parts: