 In fact, the only significant difference between Frege’s notion of a second-level concept and the modern notion of a generalized quantifier is that Frege did not have the idea of an interpretation or model, which we now (since the advent of model theory in the 1950s) see as a universe that the quantifiers range over, plus an assignment of suitable semantic objects to the non-logical symbols. Frege’s symbols all had fixed meanings, and the only universe he considered was the totality of everything. But apart from this, one may well say that it was Frege who discovered generalized quantifiers. This aspect of Frege’s logic, however, remained in the background for a long time, and model theorists in the 50s and 60s seem not to have been aware of it.