Concept
In metaphysics and ontology, Austrian philosopher Alexius Meinong advanced nonexistent objects in the 19th and 20th centuries within a "theory of objects". He was interested in intentional states which are directed at nonexistent objects. Starting with the "principle of intentionality", mental phenomena are intentionally directed towards an object. People may imagine, desire or fear something that does not exist. Other philosophers concluded that intentionality is not a real relation and therefore does not require the existence of an object, while Meinong concluded there is an object for every mental state whatsoever—if not an existent then at least a nonexistent one. The round square copula is a common example of the dual copula strategy used in reference to the "problem of nonexistent objects" as well as their relation to problems in modern philosophy of language. The issue arose, most notably, between the theories of contemporary philosophers Alexius Meinong (see Meinong's 1904 book Investigations in Theory of Objects and Psychology) and Bertrand Russell (see Russell's 1905 article "On Denoting"). Russell's critique of Meinong's theory of objects, also known as the Russellian view, became the established view on the problem of nonexistent objects. In late modern philosophy, the concept of the "square circle" (viereckiger Kreis) had also been discussed before in Gottlob Frege's The Foundations of Arithmetic (1884). Abstract object theory The strategy employed is the dual copula strategy, also known as the dual predication approach, which is used to make a distinction between relations of properties and individuals. It entails creating a sentence that is not supposed to make sense by forcing the term "is" into ambiguous meaning. The dual copula strategy was originally brought to prominence in contemporary philosophy by Ernst Mally. Other proponents of this approach include: Héctor-Neri Castañeda, William J. Rapaport, and Edward N. Zalta.