The foundational principles of CA tackle these four fundamental facts of human action by exploiting the concept of sequence (Schegloff, 2007). The basic idea is actions are simultaneously context shaped and context renewing. Current actions invite (and in some cases, mandate) responses, and in turn form the most basic and proximate context in which a next turn at talk occurs and should be understood. It is a default assumption in human conduct that a current action, should be, and normally will be, responsive to the immediately prior one. Indeed persons have to engage in special procedures (e.g., "Oh by the way...") to show that a next action is not responsive to the prior.
The inherent turn-by-turn contextuality of conversation is a vital resource for the construction of understanding in interaction.
Since each action will be understood as responsive to the previous one, the understanding that it displays is open for inspection.