Obversion and Conversion: Saying It Another Way

Tonight, two ways to say the same thing differently: obversion and conversion.

Sometimes to see it more clearly. Sometimes to persuade. And sometimes, when people turn a sentence round carelessly, to make a terrible mistake.

Obversion changes the quality of a proposition and negates the predicate: “All scholars are readers” becomes “No scholar is a non-reader”. The meaning stays the same. Every form can be obverted: A to E, E to A, I to O, O to I.

Conversion swaps the subject and predicate. E and I convert simply: “No fish is a bird” becomes “No bird is a fish”; “Some sailors are swimmers” becomes “Some swimmers are sailors”. A converts only by limitation: “All sailors are swimmers” gives only “Some swimmers are sailors”. O does not convert at all.

Turning an A round without limitation, “All thieves are liars, so all liars are thieves”, is illicit conversion. Sister Miriam Joseph also notes the rhetorical use of obversion called litotes, saying something by denying its opposite: “not bad”, “not unkind”. Shakespeare, she points out, uses it often.