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Aquinas on Conscience

1. Practical Reason

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About this Lecture


In this module, we introduce Aquinas’ account of practical reason, focusing in particular on (i) reason as an operation of the power of intellect (ii) two powers of intellect: intellectus agens, and intellectus possibilis (iii) how we use reason to deploy the intellect, and (iv) the relationship between practical reasoning and human action.


In this course Dr Daniel De Haan (University of Oxford) explores St. Thomas Aquinas’ doctrine of conscience. In the first module we introduce Aquinas’ account of practical reason, and its relevance to the doctrine of conscience. After that, we explore Aquinas’ views on the judgment of conscience in the Summa Theologica. In the third module, we look at two further features of practical reason: synderesis and prudence, before moving on to Aquinas’ take on moral responsibility. Finally, in the fifth module, we look at the demands of conscience in everyday life, and Aquinas’ challenge to ‘moral dilemmas’.


Dr Daniel De Haan is a Senior Research Fellow & Lecturer in Philosophy and Theology in the Catholic Tradition at the University of Oxford. His research interests are in philosophical theology, Christian and religious ethics, and science and religion. His most recent publications include Aquinas on Perceiving, Thinking, Understanding, and Cognizing Individuals (2019), and Approaching Other Animals with Caution: Exploring Insights from Aquinas's Psychology (2019)

Cite this Lecture

APA style

De Haan, D. (2022, February 23). Aquinas on Conscience - Practical Reason [Video]. MASSOLIT.

MLA style

De Haan, D. "Aquinas on Conscience – Practical Reason." MASSOLIT, uploaded by MASSOLIT, 23 Feb 2022,