Dharmakīrti, again following Dignāga, also holds that that things as they are in themselves are "ineffable" ("avyapadeśya"). Language is never about the things in themselves, only about conceptual fictions, hence they are nominalists. Due to this theory, the main issue for Dharmakirti becomes how to explain that it is possible for our arbitrary and conventional linguistic schemas to refer to perceptual particulars which are ineffable and non conceptual. To explain this gap between conceptual schema and perceptual content, Dharmakirti takes up Dignaga's theory of "exclusion" ("apoha"). Dignāga's view is that "a word talks about entities only as they are qualified by the negation of other things." Dharmakīrti's unique take on this nominalist theory, which underlies his entire system, is to reinterpret it in terms of causal efficacy—"arthakriyā" (which can also be translated as 'telic function', 'functionality', and 'fulfillment of purpose').