O
- O sacrum convivium"O sacrum convivium" is a Latin prose text honoring the Blessed Sacrament. It is included
- Oakville, CaliforniaOakville is a census-designated place (CDP) in the Napa Valley of Napa County, northern Ca
- Objectivity (science)Type of attempt to uncover truths
- ObligationCourse of action someone must take
- Occam's razorPhilosophical problem-solving principle
- OccamismPhilosophical and theological system of William of Ockham
- OccasionalismAll events are caused directly by God
- Oduduwa scriptThe Oduduwa script was created in 2016 or 2017 by a Beninese Yoruba chief named Tolúlàṣẹ Ò
- Oedipus AegyptiacusOedipus Aegyptiacus is Athanasius Kircher's supreme work of Egyptology.
- Of the Conduct of the UnderstandingOf the Conduct of the Understanding is a text on clear and rational thought by John Locke,
- Ole Martin MoenNorwegian philosopher
- Oliver Wendell Holmes Jr.US Supreme Court justice from 1902 to 1932
- Oliver, British ColumbiaOliver is a town near the south end of the Okanagan Valley in the southern Interior of Bri
- ỌlọrunSupreme Being in the Yoruba religion
- OmnibenevolenceProperty of possessing maximal goodness
- Omnipotence paradoxFamily of paradoxes around the definition of omnipotence
- OmniscienceProperty of possessing maximal knowledge
- On a Supposed Right to Tell Lies from Benevolent Motives1797 essay by Immanuel Kant
- On LibertyBook by John Stuart Mill
- On the Genealogy of Morality1887 book by Friedrich Nietzsche
- On the SoulTreatise by Aristotle
- On the SublimeBook by Pseudo-Longinus
- OntologyPhilosophical study of being
- OpinionJudgement, viewpoint, or statement that is not conclusive
- Oral skillsOral skills are speech enhancers that are used to produce clear sentences that are intelli
- Orator (Cicero)Rhetorical work by Cicero
- Ordinary language philosophyView that philosophical problems are distortions of natural language
- OrganicismPhilosophical and political conception of society as a living organism
- Organized religionReligion with formalized beliefs and rituals
- Organized secularismBelgian irreligious union
- OtéléOtele is a town in central Cameroon.
- Otto PöggelerOtto Pöggeler (12 December 1928 in Attendorn – 10 December 2014) was a German philosopher.
- Owen FlanaganAmerican philosopher