abstract:Subalternation is an immediate inference which is only made between A (All S are P) and I (Some S are P) categorical propositions and between E (No S are P or originally, Not every S is P) and O (Some S are not P or originally, No S is P) categorical propositions of the traditional square of opposition and the original square of opposition. If the A proposition is true we may immediately infer that I is true.