Disjunction (logic)

A logical proposition of the form “A or B”. The term can refer to either an inclusive or an exclusive “or”.

We therefore distinguish between two different types of disjunctions, for which the same word (“or”) is used in English:

The following question is an example of an inclusive disjunction:

Would you like sugar or milk in your coffee?

This usually means: sugar, or milk, or both, i.e. it uses an inclusive “or”. This is also referred to as an adjunction.

The situation is different with the following question:

“Would you like ice cream or fruit salad for dessert?”

This usually means you can have either ice cream or fruit salad, but not both, i.e. this question uses an exclusive “or”, also known as “contravalence”.

• Adjunction – inclusive disjunction: A or B (or both)
• Contravalence – exclusive disjunction: A or B (but not both)

• Affirming a disjunct – logical fallacy
• Conjunction – proposition of the form “A and B”

• Logical disjunction on Wikipedia