A consequence may have multiple causes. The absence of one cause does not, by itself, establish the absence of the consequence. This motivates the distinction between the conventional force of law and independent causal inference.
Example: “If you had come, I would have given you a book.” The book might still have reached you through some other means, unless the wording or context specifically restricts this gift to that visit.
Linking an outcome to a condition is not invariably equivalent to making that condition the sole possible cause of the outcome. The text probes this distinction at length.