It's probably intended to be analogous to something like second-order logic[1]. Where first-order logic is about individual elements and second-order logic is a

It's probably intended to be analogous to something like second-order logic[1]. Where first-order logic is about individual elements and second-order logic is about relations. [1] https://en.wikipedia.org/wiki/Second-order_logic https://en.wikipedia.org/wiki/Second-order_logic