CAP is about behavior during a network partition: a distributed data system cannot guarantee both linearizable consistency and successful responses for every request on both sides of a partition. It is not a claim that every database permanently chooses only two of three features under normal operation.

Availability in CAP has a precise meaning: each request to a non-failing node receives a response, though the response may not contain the latest data. Real systems also trade latency, durability, and consistency under normal conditions, so CAP alone is not a complete design method.

Quorum systems use replica acknowledgments. In a simplified replicated set of N nodes, read and write quorums R and W may overlap when R + W > N, helping ensure a read intersects a successful write. This arithmetic does not by itself guarantee linearizability; versions, concurrent writes, failure handling, and the database's protocol matter.