UGC NET Questions (Paper – 1)

Obversion is an immediate inference in which a categorical proposition is transformed by switching from affirmative to negative or vice versa and replacing the predicate with its complement. For example, “All S are P” becomes “No S are non-P”. This operation preserves logical equivalence for all four standard forms. Hence the result of the process described in the stem is called the obverse of the original proposition.

Option A:
Option A, conversion, involves interchanging the subject and predicate terms while keeping quantity and quality the same or appropriately modified, as in converting “No S are P” to “No P are S”. It does not require introducing the complement of the predicate.

Option B:
Option B is correct because obversion is uniquely defined by the combination of quality change and predicate complementation. It provides a reliable way of generating an equivalent statement that often clarifies the logical content.

Option C:
Option C, contraposition, is obtained by interchanging subject and predicate and negating both, which is a different transformation usually applied to conditionals and some categorical forms. It is not the simple quality change with predicate complement described in the question.

Option D:
Option D, distribution, concerns whether a term refers to all members of its class within a proposition and is not the name of any immediate inference. It does not describe the operation of forming an equivalent proposition.