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Definition of first philosophy.
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Ontology, or First Philosophy, is the science of being being original: ens; in Wolff's system, "being" refers to anything that is possible, meaning it does not contain a logical contradiction in general, or insofar as it is being.
We gave this definition in the Preliminary Discourse prefixed to the Logic (§ 73). However, this part of philosophy is called Ontology from the Greek ontos (of being) and logos (science/study) because it deals with being in general, having received its name from the object with which it is concerned. The same is usually called First Philosophy because it hands down the first principles and the first notions which are used in reasoning. Hardly any other name is more despised today than that of Ontology. For after the sterile treatment by the Scholastics Scholastics original: Scholastici; the medieval schoolmen. By the 18th century, their complex, abstract debates were often viewed by Enlightenment thinkers as useless "word-play," a reputation Wolff is attempting to repair here brought this most useful and fundamental part of philosophy into contempt, those who decide with haste have rejected it altogether, not without detriment to the sciences. We vindicate this same science from the contempt under which it suffers, by converting its sterile treatment into a fertile one.
(Wolff's Ontology.)