  The formal categories are marked by such familiar ontological divisions as those between objects, processes and relations. Following Husserl, in addition to these, Ingarden distinguishes material categories, with high-level material kinds including, e.g., works of art and real (spatio-temporal) objects. Finally, claiming there is an essential ambiguity in the term ‘exists’, Ingarden also goes on to distinguish different existential categories or “modes of being” — different ways in which entities may exist, e.g., dependently or independently, in time or not, contingently or necessarily, etc.