O
- Objectivity
- Objects of Perception
- Occasionalism
- Ockham (Occam), William of
- Omniscience and Divine Foreknowledge
- Omnipotence
- Ontological Argument for God’s Existence, Anselm’s
- Open Theism
- Ordinary Language Philosophy
- Organicism, Plato’s
- Origen of Alexandria
- Ortega y Gasset, José
- Other Minds, Solipsism and the Problem of
