ABSTRACT
Ontology as a branch of metaphysics is the science of being; it investigates the kinds of objects (abstract and concrete, existent and nonexistent, real and ideal, independent and dependent), and their in-between relations. Metaphysics is the pure part of philosophy, in contrast to the applied. The word originates from Metaphysica, the title of Aristotle’s treatise on the subject, from Greek (ta) meta (ta) physika, literally, the (works) after the physical (works) (Merriam-Webster’s Collegiate Dictionary, 2003). According to Kant (1997), the word refers to the science beyond the boundaries of nature, that is, metaphysics is the philosophy of nature so far as it is based on a priori principles. Physics is the philosophy of nature so far as it is based on principles from experience (Kant, 1790-1791?). Bolzano (1810) compares mathematics and metaphysics as the two main parts of a priori knowledge; mathematics investigates the conditions under which existence of things is possible, whereas metaphysics is concerned to prove a priori which things are real.
