ABSTRACT
This chapter discusses disjunction and disjunctive inference in the formal logic elements. The difference between the p and q operators is that a disjunction is true if both disjuncts are true, while an alternation is false if both alternatives are true. People have seen that the English expression ‘Either … or …’ conceals two dyadic truth-functional operators. In fact, it is most commonly used to express disjunction, and in general alternation is made explicit in ordinary discourse by the addition of some such phrase as ‘and not both’. Some philosophers are inclined to say that there are no occurrences in ordinary discourse of the pure truth-functional alternation. A disjunction is false only when both disjuncts are false. An alternation is true when exactly one alternative is true.
