**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 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.