How does the logical connective “or” affect the truth of a compound proposition?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

In formal logic, the connective "or" is known as disjunction and functions as a truth-function, meaning the truth-value of a compound proposition depends on the truth-values of its component parts.12

There are two primary types of disjunction to consider:

  • Inclusive Disjunction (x∨y): This is the standard interpretation in logic. A compound proposition is true if at least one of its components is true, or if both are true. It is only false if both component propositions are false.12
  • Exclusive Disjunction (x∨˙y): This asserts that one or the other component is true, but not both.1

The truth-value of these propositions can be determined using a truth table, which maps all possible combinations of truth and falsity for the components. For example, in an inclusive disjunction, if component p is true and component q is false, the resulting compound proposition p∨q is true. When evaluating arguments, disjunctions are often used to create branches in semantic tableaux, where the original disjunction is considered true if either branch is satisfied.23