The Summa makes many references to certain thinkers held in great respect in Aquinas's time. The arguments from authority, or sed contra arguments, are almost entirely based on citations from these authors. Some were called by special names:
- The Philosopher: Aristotle. He was considered the most astute philosopher – the one who had expressed the most truth up to that time. The main aim of the Scholastic theologians was to use his precise technical terms and logical system to investigate theology.
- The Commentator: Averroes (Ibn Rushd). He was among the foremost commentators on Aristotle's works in Arabic, and his commentaries were often translated into Latin (along with Aristotle's text).
- The Master: Peter Lombard. Writer of the dominant theological text for the time: The Sentences (commentaries on the writings of the Doctors of the Church)
- The Theologian: Augustine of Hippo. Considered the greatest theologian who had ever lived up to that time; Augustine's works are frequently quoted by Aquinas.
- The Legal Expert (iurisperitus): Ulpian (a Roman jurist), the most-quoted contributor to the Pandects
- Dionysius: Pseudo-Dionysius the Areopagite. Aquinas refers to the works of Dionysius, whom scholars of the time thought to be the person mentioned in Acts 17:34 (a disciple of St. Paul). However, they were most likely written in Syria during the 6th century by a writer who attributed his book to Dionysius (hence the addition of the prefix "pseudo-" to the name "Dionysius" in most modern references to these works).
- Avicenna: Aquinas frequently cites this Persian polymath, the Aristotelian/Neoplatonic/Islamic philosopher Ibn Sina (Avicenna).
- Algazel: Aquinas also cites the Islamic theologian al-Ghazali (Algazel).
- Rabbi Moses: Rabbi Moses Maimonides was a Jewish rabbinical scholar, a near contemporary of Aquinas (died 1204, before Aquinas). The scholastics derived many insights from his work, as he also employed the scholastic method.