From Nature to Norm: How to Derive 'Ought' From 'Is' – Prof. Catherine Peters

The Thomistic Institute

Christianity, Religion &Amp; Spirituality, Society & Culture, Catholic Intellectual Tradition, Catholic, Philosophy, Religion & Spirituality, Thomism, Catholicism

4.8 • 729 Ratings

🗓️ 3 October 2025

⏱️ 44 minutes

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Summary

Prof. Catherine Peters addresses the philosophical question of deriving moral 'ought' from descriptive 'is', arguing from a Thomistic natural law perspective that the essence of human nature grounds objective moral norms, bridging fact and value through teleology and reason.

This lecture was given on May 30th, 2025, at Mount Saint Mary College.

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About the Speakers:

Catherine Peters is an associate professor of medieval philosophy at Loyola Marymount University in Los Angeles, California. Her work centers on issues of philosophical anthropology, metaphysics, and natural theology. She is passionate about translating medieval thought into modern terms and applying its insights to perennial questions such as “Who am I?” “What should I do?” and “Is there a God?” A frequent presenter in both the United States and Europe, her scholarship has been published in numerous volumes and journals, including The Thomist, New Blackfriars, National Catholic Bioethics Quarterly, The Journal of Islamic Philosophy, European Journal for the Study of Thomas Aquinas, Lex Naturalis, and Jesuit Higher Education. When not in the classroom, she can often be found in local coffee shops, at the dog park, or in a HIIT class.

Keywords: Anthropology, Eternal Law, Humean Empiricism, Law and Morality, Natural Law, Naturalistic Fallacy, Practical Reason, Rational Animal, Teleology, Treatise of Human Nature

Transcript

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0:00.0	Thanks to donors like you, Aquinas 101 is setting the world aflame with the truth,
0:05.1	but the next season can't be filmed without your help.
0:08.3	Dozens of new episodes are planned, but they'll only be brought to life if you make them possible.
0:13.3	Your gift by October 31st will bring the truth to students, families, and people around the world.
0:20.8	Please use the link in the episode description
0:22.7	below to give today. Welcome to the Tomistic Institute podcast. Our mission is to promote
0:32.3	the Catholic intellectual tradition in the university, the church, and the wider public square.
0:37.4	The lectures on this
0:38.3	podcast are organized by university students at Thomistic Institute chapters around the world. To learn more
0:44.5	and to attend these events, visit us at to mystic institute.org. My presentation today will focus on the
0:52.8	issue of deriving an ought from an is. And to this end,
0:57.3	I will first consider the meaning of is within the temistic account of human nature. And second,
1:03.1	turn to the meaning of ought. And it's in this second section that I will consider both the
1:07.4	tomistic account of law in general and also the to mystic account of natural law in particular.
1:12.6	I don't have a handout. I appreciate those of you who have made them, but I am hopeful that this will help you follow where I am.
1:18.6	At the very top, you'll see that it'll change to indicate what section of the paper we're in.
1:22.6	A number of philosophers were you to ask them how to derive aught is, would likely respond, you can't, or don't.
1:32.3	Indeed, the denial that you can derive moral precepts, i.e. what you ought to do from what is, is often called the naturalistic fallacy, or perhaps the is ought fallacy.
1:43.3	A fallacy, of course, is a term that we use to refer to a mistake
1:46.7	or an error in reasoning. And the naturalistic fallacy is often formulated either as one cannot
1:52.7	derive an ought from an is, or sometimes takes the form of denying that something is good
1:57.8	simply because it is natural. Both formulations have at first some
	...

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