Throughout Arcs 1 and 2, the premises employed count as perfectly known prior to the knowledge of the Clarity and Distinctness Rule they help establish

On this interpretation, there is no vicious circularity in the broader argument, because the truths serving as premises in the arguments for the C&D Rule are perfectly knowable independently of that rule. That is, throughout the arguments of Arcs 1 and 2, the premises employed count as perfectly knowledge prior to the knowledge of the C&D Rule they help establish.