Philosophy Index

Addition

Addition or weakening is a basic rule of inference in logic by which a disjunction is formed out of a single proposition or fomula. Addition is also known as the disjunction introduction rule of inference (or ∨I), and explains that if "P" is true, then "P or Q" is also true.

Addition may be formally presented as follows:

α infers α ∨ β


Note: In this case, α may also produce β ∨ α by addition, since α ∨ β and β ∨ α are equivalent, according to the Commutative laws.