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.

Only statement D is wrong; all the others correctly describe valid immediate inferences. It is true that E and I propositions are simply convertible and that obversion preserves logical equivalence for the standard forms. From “All S are P” we cannot with certainty derive “Some P are S”, and UGC NET questions frequently ask which of these inferences are valid. However, from “Some S are not P” we cannot infer “No S are P”, since the particular negative does not entail the universal negative, making D the sole incorrect statement.

Option A:
Option A is correct because it isolates D as the only false statement and leaves A, B, C and E untouched as valid logical claims. It accurately reflects standard rules for conversion and obversion and the limits of what can be inferred from an O-proposition. This matches both logic texts and exam-style reasoning.

Option B:
Option B is incorrect since it treats A as wrong along with D, even though A correctly states that the converse of an A-proposition does not follow with certainty. Including A among the wrong statements therefore misrepresents a genuine logical restriction.

Option C:
Option C is wrong because it adds C to the set of allegedly wrong statements. C is in fact correct, as obversion yields a logically equivalent proposition in all four standard forms, so C and D only misclassifies an important logical law.

Option D:
Option D is also incorrect since it groups B with D, thereby wrongly branding the simple convertibility of E and I propositions as incorrect. B and D only thus fails to respect the standard conversion rules that students must know for UGC NET.

For an E-type universal negative proposition like "No S are P", simple conversion is valid and yields "No P are S". This new statement preserves both the quantity and quality of the original while exchanging subject and predicate. The two propositions express the same exclusion relation between the classes. Hence the correct converted form is "No P are S".

Option A:
Option A, "All P are S", changes both the quantity and the quality of the original statement. It asserts a universal affirmative rather than a universal negative and therefore cannot be logically equivalent to "No S are P".

Option B:
Option B, "Some P are S", asserts an existential particular affirmative that contradicts the universal exclusion in the original. It would claim overlapping membership where the original denies any overlap. Thus it is not a valid conversion.

Option C:
Option C is correct because the conversion of an E proposition simply reverses the positions of subject and predicate while maintaining "no" as the quantifier. This keeps the meaning that the two classes do not share any members, which is consistent with the original statement.

Option D:
Option D, "Some P are not S", changes the form to a particular negative and does not preserve the universal denial of overlap. It allows the possibility that some P are S, which conflicts with the original universal negative.

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.

Statements A, B, C, E and F are correct, while D is false. Conversion is valid for E and I forms, obversion works by changing quality and complementing the predicate, and contraposition in its full form applies to A and O in the traditional system. Obversion is valid for all four categorical forms, and exam questions can test recognition of these operations. D is wrong because simple conversion of an A proposition is not always valid; it must usually be converted to a particular form. Therefore A, B, C, E and F only is the correct combination.

Option A:
Option A is incomplete because it stops at A, B and C and leaves out E and F, which also state correct facts about obversion and exam usage. Without acknowledging that obversion is valid for all four forms and that these operations are tested, the account is partial. Hence A, B and C only cannot be accepted.

Option B:
Option B is correct because it brings together the three operations and their main properties along with their application in UGC NET questions. It rightly excludes D, which incorrectly generalises about simple conversion of A propositions. This combination fully reflects the standard treatment of immediate inferences.

Option C:
Option C is wrong since it includes D along with B, C, E and F and omits A. Accepting D means incorrectly treating simple conversion of every A as valid, and omitting A forgets the special status of E and I in conversion. This mix of error and omission makes the option unacceptable.

Option D:
Option D is incorrect because it omits B, removing the core definition of obversion, and it also drops E. Although it mentions some correct points, without B and with the absence of E it does not capture all true statements in the list. Therefore A, C, E and F only cannot be the correct answer.