|Categories: categories are basic concepts for classifying the objects of a knowledge domain into different groups or hierarchies. In philosophy, the category systems of different authors can differ considerably. Concepts which are not suitable for classifying are transcendentals, e.g. the concept of similarity. However, these concepts are again applicable to categorized objects.|
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Categories / ontology / Meixner: in the strict sense: individual, property, affairs, event
Existence / relevance / ontology / Meixner: It is not conceptually obvious that something that exists, really is - but the reverse is true: everything that exists, is real - "there is": is unclear - Meixner per empty categories, per unrealized possibility as facts, not as individuals.
Einführung in die Ontologie Darmstadt 2004