 These entities constitute a certain uniform domain, which can be viewed as a subdomain of Frege’s so-called “third realm” (the realm of the objective content of thoughts, and generally abstract objects of various kinds, see Frege 1918, cf. Popper 1972 and also Burge 1992: 634). Among the subdomains of this third realm one finds, e.g., the collection of mathematical objects (numbers, classes, etc.). The set of truth values may be regarded as forming another such subdomain, namely the one of logical values, and logic as a branch of science rests essentially on this logical domain and on exploring its features and regularities.