We previously learned about the four different types of propositions. Now, we will get to observe some interesting logical relations that exist among them. The relations are as follows:
- Contradictory Relation: when the truth of one proposition implies the falsity of the other, and vice versa, meaning that the two propositions can never both be true at the same time nor can both be false at the same time.
- Contrary Relation: when the two propositions cannot both be true at the same time (although they can both be false).
- Subcontrary Relation: when the two propositions cannot both be false at the same time (although they can both be true).
- Subalternation: when the truth of the first proposition implies the truth of the second (but not the other way around).