Obversion is a philosophical term that refers to the process of changing or negating the quality or quantity of a proposition. Some synonyms for obversion include inversion, conversion, contraposition, and reduction. Inversion is the opposite of obversion and involves a reversal of the subject and predicate of a proposition. Conversion, on the other hand, is the process of changing the subject and predicate of a proposition. Contraposition involves the negation of both the subject and predicate of a proposition. Reduction is a process that involves simplifying a complex proposition into a simpler and more manageable one. These synonyms are useful to know when studying philosophy and logic, as they can help to clarify and simplify complex concepts.