"the order being changed," c.1600, Latin, from vice, ablative of vicis "a change, alternation, alternate order" (see vicarious) + versa, feminine ablative singular of versus, past participle of vertere "to turn, turn about" (see versus). "The phrase has the complete force of a proposition, being as much as to say that upon a transposition of antecedents the consequents are also transposed" [Century Dictionary].