- Abelard, Peter (11)
- Abrabanel, Judah (2)
- Abramowski, Edward (1)
- Abravanel, Isaac (3)
- Adamson, Robert (2)
- Adelard of Bath (4)
- Adler, Mortimer J. (7)
- Adorno, Theodor W. (10)
- Aenesidemus (2)
- Agamben, Giorgio (3)
- Agrippa, Heinrich Cornelius@ (15)
- Ajdukiewicz, Kazimierz (2)
- Albert of Saxony (3)
- Albertus Magnus@ (14)
- Alcmaeon of Croton (1)
- Alcott, Amos Bronson (6)
- Alembert, Jean le Rond d' (3)
- Alexander of Aphrodisias (3)
- Alexander of Hales@ (3)
- Alexander Polyhistor@ (2)
- Alexander, Samuel (3)
- al-Farabi, Abu Nasr (3)
- al-Ghazali, Abu Hamid (7)
- Alighieri, Dante@ (58)
- al-Kindi, Yaqub ibn Ishaq (5)
- al-Razi, Abu Bakr (8)
- Alston, William P. (6)
- Althusser, Louis@ (4)
- Ambrose of Milan, St.@ (23)
- Ammonius Saccas (4)
| - Anaxagoras (8)
- Anaxarchus (2)
- Anaximander (5)
- Anaximenes (3)
- Andronicus of Rhodes (3)
- Anscombe, G. E. M. (7)
- Anselm of Canterbury, St.@ (18)
- Antiphon (3)
- Antisthenes (2)
- Apel, Karl-Otto (3)
- Apuleius of Madaura@ (4)
- Aquinas, St. Thomas@ (38)
- Arcesilaus (3)
- Archelaus (1)
- Archytas of Tarentum (2)
- Arendt, Hannah (18)
- Aristippus of Cyrene (5)
- Aristotle (69)
- Armstrong, David M. (2)
- Arnauld, Antoine (10)
- Astell, Mary (4)
- Augustine of Hippo, St.@ (129)
- Aune, Bruce (1)
- Auriol, Peter (4)
- Austin, John (1)
- Austin, John Langshaw (7)
- Averroes (11)
- Avicenna (8)
- Ayer, Alfred Jules (6)
|