  The Vaibhāṣika solution consists in the introduction of a  new type of dharma, that of appropriation (prāpti),  whose persistence in the mental stream is not due to any other  factors, including the results of past actions, but rather to its own capacity to replicate itself. The presence of a factor of  appropriation in the mental stream thus ensures the karmic  efficacy of past causal chains. It also explains why mental factors  and events remain associated with a given mental stream. This new  dharma of appropriation is classified as being dissociated from  thought and as neutral; it is also classified as being one of the  determining factors for differentiating one mental stream from  another (see AKBh ad II 35). Furthermore, it explains why  certain dispositions, such as aversion, persist in the mental stream  of an individual (because appropriation follows the initial  experience of a first moment of aversion), and how it is possible to  overcome such dispositions (when appropriation is associated with  factors that condition non-aversive states of mind). In both cases,  the concept of appropriation provides an account of continuity in the mental stream that goes against the stipulations of the Abhidharmic  principle of the momentariness of mental states. Thus, the  Vaibhāṣika solution to reconciling the theory of causality with the theory of the momentariness of all phenomena rests on a  notion that itself defies explanation, prompting traditional critics  such as Vasubandhu to ask whether appropriation is a real entity or a merely conventional one, and in the end to dismiss it altogether (see AKBh ad II 36cd). 