A disjunctive conditional does not connect A and B as “if A then B.” Instead, it states an either ... or ... relationship. The force of that relationship depends on whether the two alternatives can both be true or both be false.
The book distinguishes three cases:
True disjunction — neither both true nor both false.
Exclusion of conjunction — they cannot both be true, but they can both be false.
Exclusion of emptiness — they cannot both be false, but they can both be true.
These differences determine which inferences are valid.