Contraposition inference rule – UGC NET Question

Contraposition is an operation that takes a conditional or certain categorical propositions and transforms them by swapping subject and predicate while also negating each. For example, “If p, then q” becomes “If not q, then not p”, and these are logically equivalent. This method is often used in proofs because the contrapositive of a true conditional must also be true. Thus the inference described in the stem is contraposition.

Option A:
Option A, conversion, simply interchanges subject and predicate without negating them, as when “No S are P” is converted to “No P are S”. It does not include the additional step of negation that characterises contraposition.

Option B:
Option B, obversion, changes the quality of a proposition and replaces the predicate with its complement but does not interchange subject and predicate. It is a different immediate inference.

Option C:
Option C is correct because contraposition uniquely combines reversal of order with negation of both terms, yielding a statement equivalent to the original under classical logic for suitable forms. This fits the description given in the question.

Option D:
Option D, equipollence, is sometimes used to describe equivalence obtained by combining operations like obversion and conversion, but it is not the standard name for the specific transformation outlined in the stem.