ontological/ontology

"Philosophy for Beginners" を読んでいます。

Ontological Argument
Nealy a thousand years ago, a philosopher and monk called Anselm of Canterbury put forward what's known as the ontological argument. He said that there was something about the very idea of God that compels you to agree that God must exist. If you struggle to get your head round it, don't warry. The language is tricky:

"ontological" は形容詞なので元の "ontology" で辞書を見ます。
・Oxford English Dictionary: a branch of philosophy that deals with the nature of existence
・Collins Dictionary: Ontology is the branch of philosophy that deals with the nature of existence.: ...the ontological question of the relationship between mind and body.
・Vocabulary.com: If you are interested in metaphysics and the meaning of existence (and want to impress your friends), ontology may be a good field of study for you.
Ontology comes from two Greek words: on, which means "being," and logia, which means "study." So ontology is the study of being alive and existing. Heady stuff, but something we all ponder at one point or another. When you see the word ontology, think of Hamlet agonizing over "To be, or not to be" or Descartes stating "I think, therefore I am."

最後に引用したVocabulary.comの説明は分かり易いですね。