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How does the logical connective “or” affect the truth of a compound proposition?
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Formal logic
Alfred North Whitehead.
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 (): 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 (): 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 is true and component is false, the resulting compound proposition 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