The main difference between the old and the new metaphysics is in the philosophical problems they seek to address. The old metaphysics, going back up to the Ancient Greek philosophers such as Parmenides and Aristotle, was preoccupied with the matters of essence and existence. The classic example of a problem characteristic for the old metaphysics would be the existence of universals. In the metaphysical sense, “universal” refers to the superficial essence of a given type of object that allows classifying and recognizing them as such Platonic “ideas” or “forms” are likely the best-known example of universals in Western philosophy. The debate between nominalism and realism – whether universal exist in the strict sense of the word – is the central problem of the old metaphysics. Thus, the old metaphysics largely focused on separating itself from ontology by drawing the line between postulating things and proving their existence.
The new metaphysics is an umbrella term covering the resurgence of interest in metaphysical topics in the second half of the 20th century. New metaphysics incorporates many problems of the old but pays more attention to modalities – that is, the types of relations between propositions and reality. The old metaphysics was mostly preoccupied with the things that are supposed to be forever unchangeable: if there is a universal essence of a table, it should always be self-same. The new metaphysics, on the other hand, also assesses the propositions regarding the existence and properties of changing things. It studies these propositions to establish the difference between being necessarily true – that is, true under all conceivable circumstances – or contingently true. Thus, the new metaphysics leans closer toward epistemology, just like the old metaphysics shaped itself through identifying its relation to ontology.