"Derive absurdity" comes from the fact that in these logics there is only one statement which is "Absurdity"—capitalized perhaps. It's a unique thing to talk ab

"Derive absurdity" comes from the fact that in these logics there is only one statement which is "Absurdity"—capitalized perhaps. It's a unique thing to talk about and "an absurd conclusion" is actually shorthand for "a statement from which you could derive Absurdity".