Introduction.- Frege's Distinction Between "Falling Under" and "Subordination".- Scotus, Frege and Bergmann.- Zermelo and the Axiomatic Method.- Between Bernays and Carnap.- On the Motivations of Goedel's Ontological Proof.- The Ontological Regress of Maddy's Mathematical Naturalism.- What If Haecceity Is Not a Property?.- Epilogue.