- In an Aristotelian tradition, metaphysics comprises two topics: the nature of God, understood as a first cause or "unmoved mover;" and the description of all that is, i.e., ontology.
- Study of things not accessible by the senses. Plato's theory of forms is a paradigm case of a metaphysical theory, because the forms, which are something like universals, cannot be detected by use of any of the 5 senses, and do not exist in space or time. In the first half of the 20th century, "metaphysics" was often used in a derogative sense by philosophers who strongly promoted empiricism. This derogatory sense of the term is becoming weaker as more philosophers take up issues concerning entities that cannot be detected with the sense. For instance, Barry Smith explicitly rejects anti-metaphyical points of view about ontology.