saginthesun described that metaphysics is the study of the fundamental nature of reality. It is concerned with the first principles of existence, identity and change, space and time, cause and effect, necessity and possibility. The term “metaphysics” was coined by Andronicus of Rhodes in the first century BC, and it was meant to group together works that came after Aristotle’s writings on physics.

There is a wide range of topics that are included within the domain of metaphysics: composition of complex entities (such as tables, turtles, and angry mobs), the identity and persistence of objects, problematic kinds of entities (that is, entities about which it is unclear whether or in what sense they exist at all, like numbers and fictional objects such as unicorns), and many more.

This includes reduction of macro-level entities (molecules, atoms, and subatomic particles) to their constituent parts, such as the hydrogen atom; reduction of properties to sets of objects which resemble them; reduction of states of affairs to entities and properties, including relations; and reduction of the mental to the physical.

Several important philosophers made contributions to this area, including Thales of Miletus in the 6th century BCE and Gottfried Leibniz in the 17th century. The earliest Greek philosophers, such as Thales and his fellow Miletians Anaximander and Anaximenes, posited the existence of monads, or underlying principles, which they thought were indestructible and beyond the power of human perception.

Reduction is also an important theme in metaphysics, particularly in the realm of the sciences. This involves the question of whether or not it is possible to express all of the theories in the physical sciences in terms of their key axioms, such as the axiom that matter is composed of atoms, particles, and forces.

Some modern philosophers argue that the idea of reduction should be replaced by the idea of emergence, or that all the axioms in a theory are true as a result of some process that is ongoing. This approach, while a controversial one, is considered to have more scientific merit than the alternative, which is to believe that the axioms in a science theory are true as of the moment of its formulation.