absolute
Adams, John (1735–1826)
Addison, Joseph (1672–1719)
Albertus Magnus (1193–1280)
Alembert, Jean Le Rond d' (1717–1783)
analogy, argument from
Anaxagoras of Clazomenae (c. 500–c. 428 BC)
Anaximander of Miletus (c. 610–c. 540 BC)
Anaximenes of Miletus (c. 585–525 BC)
ancient philosophy, related to the possibility of extraterrestrial life
Aquinas, Thomas (1225–1274)
Aristotle of Stagira (384–322 BC)
associationism
Averroës (1126–1198)
axiom
axiomatic method

Bacon, Francis (1561–1626)
Bacon, Roger (c. 1214–c. 1292)
Baker, Thomas (1656–1740)
Barnes, Ernest William (1874–1953)
Beattie, James (1735–1803)
Beck, Lewis White (1913–1997)
Bentley, Richard (1662–1727)
Bergson, Henri (1859–1941)
Berkeley, George (1685–1753)
Bernardin de Saint-Pierre, Jacques Henri (1737–1814)
Bohm, David Joseph (1917–1992)
Bolingbroke, Henry St. John (1678–1751)
Bonnet, Charles (1720–1793)
Borel, Pierre (c.1620–1671)
Borges, Jorge Luis (1899–1986)
Boscovich, Roger Joseph (1711–1787)
Brewster, David (1781–1868)
Bridgman, Percy Williams (1882–1961)
Büchner, Ludwig (1824–1899)
Buridan, Jean (c.1295–1358)

Cambridge Platonists
Campanella, Tommaso (1568–1634)
Carnap, Rudolf (1891–1970)
category
causality
Chalmers, Thomas (1780–1847)
common sense school
Comte, Auguste (1798–1857)
conceptualism
Confucius (c. 551–479 BC)
Coyne, George V. (1933–2020)

de Concilio, Januarius (1836–1898)
deism
Democritus of Abdera (c .470–400 BC)
Derham, William (1657–1735)
Descartes, René (1596–1650)
determinism
Dewey, John (1859–1952)
Diderot, Denis (1713–1784)
dualism
du Prel, Carl Freiherr (1839–1899)

Empedocles (c. 490–430 BC)
empiricism
Enlightenment, The
Epicurus (341–270 BC)
essence

Fontanelle, Bernard le Bovier de (1657–1757)
formalism
free will
Frege, Friedrich Ludwig Gottlob (1848–1925)

Gassendi, Pierre (1592–1655)
Gettier problem
God
Great Monad
Green, Thomas Hill (1836–1882)

Hegel, Georg Wilhelm Friedrich (1770–1831)
Heraclitus (c. 540–c. 480 BC)
Hobbes, Thomas (1588–1679)
Hutton, Richard Holt (1826–1897)
Hume, David (1711–1776)

idealism
infinity
instrumentalism

James, William (1842–1910)
Jefferson, Thomas (1743–1826)

Kant, Immanuel (1724–1804)

Leibniz, Gottfried Wilhelm von (1646–1716)
Leucippus (5th century BC)
Locke, John (1632–1704)
logic
logic and the tools of philosophy
logical positivism
Lucretius (c. 99–55 BC)

Mach, Ernst (1838–1916)
Malebranche, Nicolas (1638–1715)
Mascall, Eric Lionel (1905–1993)
materialism
medieval philosophy, related to the possibility of extraterrestrial life
metaphysics
Metrodorus of Chios (4th century BC)
monism

natural theology
Nicholas of Cusa (1401–1464)
nothing

Ockham (Occam), William of (c. 1280–1347)

Paine, Thomas (1737–1809)
Parmenides (fl. c. 475 BC)
Peirce, Charles Sanders (1839–1914)
perception
phenomenology
philosophy
philosophy, fields
philosophy and ethics
philosophy and religion
Plato (428–348 BC)
pluralism
Plutarch (c. AD 46–120)
Popper, Karl Raimund (1902–1994)
positivism
pragmatism
pre-Socratic philosophy
process philosophy
Proclus Diadochus (c. AD 410–485)

Quine, Willard Van Orman (1908–2000)

rationalism
realism
reductionism
Reynaud, Jean (1806–1863)
Russell, Bertrand Arthur William (1872–1970)
Ryle, Gilbert (1900–1976)

scientific method
skepticism
Socrates (c. 469–399 BC)
solipsism
Spencer, Herbert (1820–1903)
Spinoza, Baruch (1632–1677)
Stewart, Dugald (1753–1828)
Swedenborg, Emanuel (1688–1772)

Teilhard de Chardin, Pierre (1881–1955)
teleology
Teng Mu
Theophrastus (c. 370–c. 285 BC)
truth

universal
Ussher, James (1581–1656)

vitalism
Vorilong, William (d. 1463)

Whewell, William (1794–1866)
Whitehead, Alfred North (1861–1947)
Wittgenstein, Ludwig (1889–1951)

Xenophanes (c. 570–475 BC)

yin and yang

Zeno of Elea (c. 450 BC)