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L ogic In traditional logic, an operation that obtains a proposition by interchanging the subject term and predicate term of another proposition. The resultant proposition is called the converse of the original proposition. For instance, the converse of SAP (“All s are p”) is “All p are s.” Of the four basic categorical propositions in traditional logic, the converse of SEP and that of SIP are valid, for they do not involve a change of quantity. Hence, they are also called simple conversions. The converse of SAP and of SOP are invalid, for they involve a change of quantity. They are also called conversion per accidens . In modern logic, conversion refers to an operation that infers a conclusion by interchanging the positions of the antecedent clause and the consequent clause, that is, from “If p then q” to “If q then p.” This is invalid. “We convert a proposition when we transpose the terms of the original proposition.” D. Mitchell, An Introduction to Logic ... log in or subscribe to read full text