This chapter sits in the middle of Thread 7: State Machines.
Chapter 1 established the atomic unit — a single statement with a
truth value. This chapter adds the connectives that combine atomic
statements into compound ones. Compound statements are the building
blocks of compound state: a system that is simultaneously in multiple
conditions. A request is
authenticated AND authorized AND rate_not_exceeded. A
distributed node is
leader AND quorum_reached AND log_committed. Every compound
state in every system you will build is a logical expression over atomic
propositions.
The direction is: atomic propositions (Ch 1) → compound state (this chapter) → compound state in state machines (Ch 13) → stateless design in distributed services (Book 3, Ch 3).
The backward link: this chapter also activates Thread 12 (Tradeoffs). The exponential complexity introduced by combining boolean variables — the subject of Chapter 3 — is a direct consequence of the combinatorial space opened by logical operators.