ABSTRACT
Applied scientific ontology is to identify the ultimate kinds or categories of existent entities that one's need, not only for science but for all meaningful thought. In contrast with physical objects and physical states of affairs, one may find it necessary to require convincing philosophical arguments to satisfy natural scepticism about the existence of putative entities that one's do not directly experience in sensation, such as abstract entities, especially numbers and universals, propositions, minds and God. The point holds with respect to all four of these categories, with appearance arguably being the least variable, and substance, transcendence and finally reality itself occupying the most hotly contested philosophical territory. Reality and the ontological status of appearance is true in the philosophy of Plato, Descartes, Kant, Schopenhauer, J. M. E. McTaggart and many other ontologists. The appearance reality distinction, epistemically prominent as it is in Descartes's methodology, never assumes a permanent place in his applied scientific ontology.
