  In his Investigation of the Cognitive Support Dignāga takes up, as the title suggests, one of the specific issue debated by Vasubandhu in his Twenty Verses: what exactly should count as an object of cognition? Dignāga's definition of the cognitive support invokes the principle of the concomitance of cause and effect (kāryakāraṇabhāva). Thus, for an object to count as a support (ālambana) for cognitive awareness it must (i) produce a cognition, and (ii) that cognition must take the form of the object (see APV ad Iad). In large measure Dignāga follows Vasubandhu's line of argumentation in his refutation of the realistic atomism of the Vaibhāṣikas (and of the Nyāya-Vaiśeṣika tradition). His innovations consist mainly in appealing to the principle of the coexistence of cause and effect and to the Yogācāra theory of mental aspects. As proof that internal aspects, which provide a basis for cognition, arise simultaneously with cognition itself, Dignāga cites the principle of the concomitance of cause and effect (kāryakāraṇabhāva): although the causal relation is understood sequentially, by virtue of the necessary dependence of cause and effect, whenever a cause is present its effect must also be present. The theory of cognitive aspects serves to further demonstrate that it is the appearance of an internally cognizable aspect that is the actual cognitive support. Because cognitions which arise taking the form of an apparently external object are the determining factor for the arsing of subsequent cognitions, the external object (say, a visible entity) and the sense faculty (visual sense) are merely projective aspects of this initial aspectual cognition (APV ad VII b). 