 Another conception of novelty whose purpose is to bolster the ultimate argument for realism is ‘functional novelty’ (Alai 2014). A datum d is ‘functionally novel’ for theory T if (1) d was not used essentially in constructing T (viz., there is a heuristic path to T and related auxiliary hypotheses that does not cite d), (2) d is a priori improbable, and (3) d is heterogeneous with respect to data that is used in constructing T and related auxiliary hypotheses (i.e. d is qualitatively different from such data). Functional novelty is a ‘gradual’ concept insofar as a priori improbability and data heterogeneity come in degrees. If there is more than one theory for which d is functionally novel then the dispute between these theories cannot be settled by the ultimate argument (Alai 2014: 306). 