This article pursues the idea of inferring aspects of phonological underlying forms directly from surface contrasts by looking at optimality theoretic linguistic systems (Prince & Smolensky, 1993/2004). The main result proves that linguistic systems satisfying certain conditions have the faithful contrastive feature property: Whenever 2 distinct morphemes contrast on the surface in a particular environment, at least 1 of the underlying features on which the 2 differ must be realized faithfully on the surface. A learning procedure exploiting the faithful contrastive feature property, contrast analysis, can set the underlying values of some features, even where featural minimal pairs do not exist, but is nevertheless fundamentally limited in what it can set. This work suggests that observation of surface contrasts between pairs of words can contribute to the learning of underlying forms, while still supporting the view that interaction with the phonological mapping will be necessary to fully determine underlying forms.