Bernays' idea of the power-set is neither univocal nor ambiguous. according to its domain of application it has a different mathematical meaning in spite of its identical logical definition. in his last axiomatisation of set-theory bernays' introduced a very powerful axiom stating that every property of the universe of all sets is mirrored by some set. this is a most peculiar application of the general--philosophical and theological--principle of analogy as a key principle in the foundations of mathematics.