Frege on the introduction of real and complex numbers by abstraction and cross-sortal identity claims

Abstract In this article, I try to shed new light on Frege’s envisaged definitional introduction of real and complex numbers in Die Grundlagen der Arithmetik (1884) the status cross-sortal identity claims with side glances at Grundgesetze (vol. 1893, vol. II 1903). As far as can see, topic has not yet been discussed context . show why strategy case projected definitions is modelled his cardinal two steps, tentatively via a contextual definition finally definitively an explicit definition. argue that leaves few important questions open, particular one relating envisioned abstraction principles for another concerning proper handling claims.