Aquinas and Beyond

Aquinas and Beyond

A Guided Tour of the Summa

What is Falsity?

What Truth Isn't

Alex Spieldenner's avatar
Alex Spieldenner
Jun 17, 2026
∙ Paid

This is the Guided Tour of the Summa Theologiae, a project for all paid subscribers of Aquinas and Beyond. In it, we are carefully reading through St. Thomas Aquinas’s masterpiece, with help from experts on Aquinas, to think like the universal doctor of the Church. Stop feeling intimidated by Aquinas, and subscribe so you can read along!


Last week, we addressed Aquinas’s description of truth. Now, we are going to talk about falsity.

You can’t take a picture of falsity, but here’s a picture of Aquinas.

As always, here are some resources you might find helpful as we move forward:

  1. The Summa Theologiae itself. Buy Prima Pars here, and the whole Summa here. Read it for free here.

  2. If you have never read the Summa, it can be a little intimidating. But I put together a roadmap so that anybody can read it and understand it. Get it here.

  3. Here is the commentary I will be using from Walter Farrell, O.P.

  4. Here is the commentary I will be using from Brian Davies, O.P.

Now, let’s dive into falsity.


Question 17: Falsity

1. Is Falsity in Things?

Just like how truth exists primarily in the intellect, falsity too exists primarily in the intellect. Again, this is because falsity can primarily be attributed to beliefs, which are combinations and divisions of ideas.

However, there is a different sense of falsity that Aquinas thinks can be said to be in things, though it is in more of an extended sense.

This falsity has to do with how our own minds relate to things outside of us. If something is created by a person but does not correspond to the intended function or purpose of the creator, it is “false” in that sense. Likewise, if something consistently is deceiving, you might call it false in a sense.

However, nothing is false in itself because, to the extent that it exists, it is true. Davies writes of things that

They are true or false only insofar as they are truly or falsely grasped by our minds—though we can, with qualification, speak of things being false in that they do not measure up to some standard or are in some way fake, like “false teeth.”1


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  • A guided tour through the ENTIRETY of Thomas Aquinas’s Summa Theologiae, which you are reading right now! Don’t miss out on forming your mind according to the Universal Doctor of the Church!

  • Founding Members get a FREE copy of my Catholic Philosopher In A Year Reading Plan, my ultimate reading list to get up to speed in Catholic Philosophy.

  • Blogs on the philosophy of religion (God, evil, free will, etc.) like this one about art and the problem of evil.

  • Reader’s Guides on the great works of Catholic philosophy, like last month’s guide on Jacques Maritain’s Art and Scholasticism.

  • Further reading recommendations on many posts, including free posts.

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