A pair of sentences are logically equivalent if and only if it is not possible for one of the sentences to be true while the other sentence is false. A pair of sentences may turn out true under exactly the same circumstances.The two sample sentences above express quite different beliefs.The following statements are logically equivalent:"All radically egalitarian societies are societies that do not preserve individual liberties"."No radically egalitarian societies are societies that preserve individual liberties". Syntactically, (1) and (2) are derivable from each other via the rules of contraposition and double negation.Semantically, (1) and (2) are true in exactly the same models.Thus they are logically equivalent. Note that this doesnt mean that they "say the same thing". Therefore, "No radically egalitarian societies are societies that preserve individual liberties" is obverse to the given statement and it is logically equivalent.