 Another nominalistic thread in the literature concerns the suggestion that sentences about (posited) abstract objects are quasi-assertions, i.e., not evaluable as to truth or falsehood (see Yablo 2001 and Kalderon 2005). Still others argue that we should not believe sentences about abstracta since their function, much like the instrumentalism discussed earlier, is to ensure empirical adequacy for observational sentences (Yablo 1998). This may involve differentiating between apparent content, which involves posited abstract objects, and real content, which only concerns concrete objects (Yablo 2001, 2002, 2010, 2014). (For more on these fictionalist accounts, see Kalderon 2005, Ch. 3, and the entry on  fictionalism.)