 Nevertheless, the very notion of the plurality of dharmas as the building blocks or the final units of analysis of sentient experience signifies a considerable shift in the Buddhist understanding of dharma. Abhidharma thought was gradually drawn into espousing a naturalistic explanation of dharmas as the fundamental constituents of the phenomenal world, increasingly associating dharmas as primary existents. The category of the unconditioned within the dharma taxonomy also asserted the possibility of enduring or permanent dharmas, in contrast to all other dharmas that arise and cease through causal interaction. The Abhidharma exegesis, then, occasioned among Buddhist circles doctrinal controversies that could be termed ontological around such issues as what the nature of a dharma is; what, in the internal constitution of a dharma, makes it the very particular it is; the manner of existence of dharmas; the dynamics of their causal interaction; and the nature of the reality they constitute. The distinctive principles and their ensuing ontological interpretations constructed by the Buddhist schools were largely shaped by a radical construal of impermanence as momentariness.