- St. Anselm of Canterbury
- St. Thomas Aquinas
- Aristotle
- David Malet Armstrong
- Alain Badiou
- Gustav Bergmann
- Bernard Bolzano
- Franz Brentano
- Mario Bunge
- Rudolf Carnap
- Ernst Cassirer
- Gilles Deleuze
- Jacques Derrida
- Rene Descartes
- Hans-Georg Gadamer
- Al-Ghazali
- Nicolai Hartmann
- Georg Wilhelm Friedrich Hegel
- Martin Heidegger
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- Heraclitus of Ephesus
- Edmund Husserl
- Roman Ingarden
- Peter van Inwagen
- Immanuel Kant
- Gottfried Leibniz
- Stanisław Leśniewski
- Leucippus
- David Kellogg Lewis
- E.J. Lowe
- Alexius Meinong
- Friedrich Nietzsche
- Nagarjuna
- William of Ockam
- Parmenides
- Charles Sanders Peirce
- Plato
- Plotinus
- Proclus Lycaeus
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- W. V. O. Quine
- Bertrand Russell
- Gilbert Ryle
- Jean-Paul Sartre
- Jonathan Schaffer
- Adi Shankaracharya
- Arthur Schopenhauer
- Duns Scotus
- Theodore Sider
- Peter Simons
- Barry Smith
- Baruch Spinoza
- Peter van Inwagen
- Achille Varzi
- Swami Vivekananda
- Alfred North Whitehead
- Ludwig Wittgenstein
- Dean Zimmerman
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