  Category theory also bears on more general philosophical questions. From the foregoing disussion, it should be obvious that category theory and categorical logic ought to have an impact on almost all issues arising in philosophy of logic: from the nature of identity criteria to the question of alternative logics, category theory always sheds a new light on these topics. Similar remarks can be made when we turn to ontology, in particular formal ontology: the part/whole relation, boundaries of systems, ideas of space, etc. Ellerman (1988) has bravely attempted to show that category theory constitutes a theory of universals, one having properties radically different from set theory, which is also seen as a theory of universals. Moving from ontology to cognitive science, MacNamara &amp; Reyes (1994) have tried to employ categorical logic to provide a different logic of reference. In particular, they have attempted to clarify the relationships between count nouns and mass terms. Other researchers are using category theory to study complex systems, cognitive neural networks, and analogies. (See, for instance, Ehresmann 2018, Ehresmann &amp; Vanbremeersch 1987, 2007, Healy 2000, Healy &amp; Caudell 2006, Arzi-Gonczarowski 1999, Brown &amp; Porter 2006.) Finally, philosophers of science have turned to category theory to shed a new light on issues related to structuralism in science. (See, for instance, Brading &amp; Landry 2006, Bain 2013, Lam &amp; Wüthrich 2015, Eva 2016, Lal &amp; Teh 2017, Landry 2007, 2012, 2018.)