The Reflection Principle encapsulates the essence of ZF set theory, for as shown by Levy (1960), the axioms of Extensionality, Separation, and Foundation, together with the Reflection Principle, formulated as the axiom schema asserting that each formula is reflected by some set that contains all elements and all subsets of its elements (note that the \(V_\alpha\) are like this), is equivalent to ZF.