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Thomistic Value of Self-Knowledge

What is the value of self-knowledge in Aquinas's thought? What might a "Thomistic" account of self-knowledge's value look like today?

Below you will find a PDF of the poster presentation I gave at the American Catholic Philosophical Association Annual Meeting on November 18, 2022. The PDF is accompanied by additional text commenting on each section of the poster. I have also included some speculations about what an account of self-knowledge's value might look like that is informed by Aquinas's thought but that develops beyond what Aquinas himself might say.

***The materials and content of this page are part of ongoing research and works in progress. Please do not hesitate to contact me if you would like to discuss or learn more.***

1. Aquinas on Self-Knowledge

Understanding the value of self-knowledge in Aquinas's thought requires understanding Aquinas's view of what kinds of self-knowledge we can have and how we can achieve them.


Broadly speaking, Aquinas distinguishes between a kind of self-awareness we have via our cognitive acts and a kind of knowledge of the nature of our soul. This self-awareness occurs via a cognition of one's own acts and is the ground for a certain kind of awareness of one's facticity. As Aquinas says in De Veritate (DV) 10.14 ad 2 "No one has ever made the mistake of not perceiving that he was alive, a fact which belongs to the knowledge by which one knows in its singularity what goes on in his soul.” While Aquinas's description here is a bit cryptic, and there is debate as to the exact character of this self-awareness (1), he generally seems to have an idea that we are aware of ourselves in our actions. This idea is similar to contemporary theories holding that consciousness involves self-consciousness (2) or that there is a kind of for-me-ness to our experiences that is part of its subjective character (3).

Self-Knowledge (of One's Nature)

To be aware of myself in this way, i.e. to be aware that I exist in my acts, does not mean I know what  I am. Awareness that I am thinking does not mean that I know what it means to think or what the power of thought is. Further knowledge of what one is, one's nature, is the second kind of cognition mentioned above that we can properly call self-knowledge or quidditative self-knowledge (4). We achieve this kind of self-knowledge through a further, careful investigation of our acts (5). Aquinas provides an example of this process in De Veritate 10.8. For example, I reflect on my thinking about cats and begin to wonder about the character of my thinking itself. I notice that the object of my thinking, catness, is a universal and that to the extent it is universal, it is immaterial. Realizing the object of my thought is immaterial, I realize that my act of thinking must itself be immaterial and thus that my power of thought must be immaterial. Ultimately, I am led to conclude that the nature of my soul (the principle of my powers) must itself also be immaterial. This process might be done in an reflective way, as just described, but might also involve others through discussions about the nature of human actions and reflections on one's own experience.

Self-Knowledge (of One's Habits)

In addition to knowing one's nature, Aquinas also holds that we can know the habitus or habits that exist in our soul. These habits are acquired dispositions, like virtues and vices, that we can come to recognize in ourselves in a similar way through attention to our actions. Yet, knowledge of our habits presupposes a knowledge of what the habit is in order for it to be identified in us (6). In order to know if I am just, first I must have an idea of what justice is. For example, I look to just individuals in the world and see how they act, I study what they say about justice, etc. and once I have an idea of what justice is, I look to my own acts to see if they are just. It is my actions that reveal my habits, for habits are a certain kind of potency for a certain kind of action. Without the actions, there is no way of knowing if the relevant habit exists.

2. Aquinas on the value of knowing/knowledge

All Knowledge is Good

For Aquinas, what is good for a thing is what perfects it according to its nature. To be sharp perfects a knife, since the nature a knife is to cut. For certain animals, we might think their nature suits them to a certain way of life. For example, hunting dogs are well suited to tracking and retrieving, so doing these things well perfects a hunting dog. For humans, our nature is distinct from other animals in that it we are rational. This means our distinctive way of life is a rational one and so performing rational activities well perfects or fulfills our nature. All knowledge is good for Aquinas insofar as it "perfects" or fulfills our unique rational powers. So self-knowledge is good insofar as it is knowledge, but that does not tell us anything about whether it is uniquely valuable. To answer this question, it is helpful to look at further distinctions Aquinas makes between the ways that instances of knowledge as theoretical or practical might be "praised" or "honored".

Practical knowledge versus theoretical knowledge 

In his Commentary on De Anima (7)Aquinas writes that certain kinds of knowledge are practical and certain kinds are theoretical. He distinguishes these kinds of knowledge according to their purpose, writing that the practical kinds are for the sake of some accomplishment whereas the theoretical kinds are for their own sake. He says that practical knowledge is "merely praiseworthy," while theoretical knowledge is worthy of special "honor". We might say that practical knowledge is instrumentally valuable, while theoretical knowledge is intrinsically or finally valuable (more on this in the final section). Aquinas's draws further distinctions between theoretical and practical knowledge in ST  I q14 a16 and these distinctions are briefly stated in the poster above. These will be important for considering what kind of knowledge self-knowledge is in the next section.


Comparing Values of Knowledge

Besides the distinction between practical knowledge as praiseworthy and theoretical knowledge as honorable, Aquinas makes a broad distinction in his Commentary on De Anima between the value of an act as based on its object and type or mode. A house built on firm foundations is worth more than the same house built less well (the mode or quality of the act makes a difference in value). However, a well built school is worth more than a well built house (the difference in object makes a difference in value). When it comes to knowledge, the object known and the certainty with which it is known make a difference to the value of the knowledge, so that knowledge of higher things is more honorable than lower things, and more certain knowledge is worth more than less certain knowledge. But what about lower things known with certainty compared to higher things known only with probability? Here Aquinas follows Aristotle in thinking that we value probable knowledge of the highest things more than certain knowledge of lower things (8). 

How this applies to self-knowledge is the topic of the next section.

3. Thomistic Value of Self-Knowledge

There are two broad results from applying Aquinas's criteria for theoretical and practical knowledge to self-knowledge.


Value of Knowing One's Own Nature

One result is that knowledge of one's nature can be considered clearly as a kind of theoretical knowledge, which would make it intrinsically valuable. Not only is self-knowledge of one's nature good insofar as it perfects oneself (just like all knowledge), but it is also valuable for itself as a kind of theoretical knowledge. However, this would not make it uniquely valuable.


What might make it uniquely valuable is the way in which it is both certain and high in status. Not all theoretical knowledge is certain, such as knowledge of angels and God. And not all certain knowledge is high in status, such as knowledge of the nature of triangles. In self-knowledge, because of its grounding in self-awareness or experience, we have a kind of knowledge both certain and high in status. As quoted above in section 1, self-awareness is uniquely certain in that we cannot be mistaken that we are acting and insofar as knowledge of our nature proceeds from this awareness or is confirmed in our own self-experience, it would seem to be more certain than our knowledge of angels or God. And while we might know about other objects with more certainty, human beings are the creatures highest in status below the angels and God, making knowledge of human nature unique in its place in both status and certainty.

Value of Knowing One's Habits

The other result is that knowledge of one's habits appears as a kind of mixed knowledge. In its mode, insofar as it involves knowing what the nature of the habit in question is, it appears theoretical. As Aquinas writes in DV 10.9, one cannot know if they have the habit of chastity without knowing what chastity is. Yet this kind of theoretical knowledge is not yet a knowledge of one's own habits. The object of knowledge in knowing one's habits is not the habit as abstractly considered, but the habit as it exists in oneself. One's habits are practical objects insofar as they are under one's control, so one might think of knowledge of one's habits as a mix of theoretical and practical knowledge, or as a kind of theoretical knowledge applied to practical objects.

Ultimately, we also want to consider the end of such knowledge. What is it for? What is the purpose of knowing one's habits? Here there seem to be clear practical implications insofar as such knowledge is necessary for self-improvement and for reflecting on our own ethical lives. But such knowledge might be worth having for itself (intrinsically valuable) if we think it is better to know our habits than to not know them, regardless of the use of such knowledge.

4. Contemporary Comparison

Finally, how does this account compare to other contemporary philosophical accounts of self-knowledge's value?

Intrinsic vs Final vs Constitutive Value

We have in Aquinas's thought, grounds for knowledge of one's nature as intrinsically valuable and knowledge of one's habits as instrumental. Yet Aquinas himself does not frame his discussion in these terms. He begins with the idea that all knowledge is good insofar as it perfects us. Then says that practical knowledge is praiseworthy and theoretical knowledge is honorable. Is it right to equate praiseworthiness with instrumental value and honorability with intrinsic value? One way of defining intrinsic value of an object is to say that the object is valued for itself in virtue of itself. Applied to theoretical knowledge, this would be to say that it is valued for itself in virtue of itself. One reason to think this might not be right is that theoretical knowledge, as a species of knowledge in general, is valued in virtue of its way of perfecting a human being. In this light, it might be better to say theoretical knowledge is finally valuable (value for itself in virtue of another good) or constitutively valuable (valued as partially constitutive of a good). In the case of practical knowledge as praiseworthy we might raise similar questions.

Agreement on Practical Value of Self-Knowledge

In comparison to contemporary accounts of self-knowledge's value, we might find points of agreement and disagreement. Quassim Cassam (2014)(9) argues that what he calls substantial self-knowledge is instrumentally valuable as well. Substantial self-knowledge includes such things as one's emotions, desires, character traits, strengths and weakness, and so there is some overlap between Cassam and Aquinas insofar as both would agree knowledge of one's habits is instrumentally valuable or worthy of praise for what it achieves. 

Disagreement on "Intrinsic Value" of Self-Knowledge

On the other hand, Cassam (2014) rejects the idea that self-knowledge (of any kind) is necessary for well-being or of any intrinsic value. He does not address knowledge of one's nature as a kind of self-knowledge and his account of substantial self-knowledge argues for such knowledge as purely of instrumental value, in no way valuable for itself or intrinsically valuable. Aquinas's account of knowledge of one's own nature, in contrast, might appear as intrinsically valuable or worth having for itself.

Yet it is not clear that we desire to know what we are solely for the sake of knowing what we are. Although self-knowledge of our nature seems clearly theoretical, we might wonder if it is really worth knowing for its own sake. Maybe it is, in the same way we think other kinds of knowledge (such as mathematical knowledge) are worthy of studying for their own sakes.

But perhaps there is more to this kind of knowledge of our nature. Maybe it has some value in living a good life that Aquinas does not explicitly discuss, or perhaps there are resources in Aquinas's thought for bringing such knowledge to bear on a good life. These kinds of considerations and further questions move us beyond the application of Aquinas's framework presented here and into further studies. 


(1) Therese Cory, Aquinas on Human Self-Knowledge. Cambridge University Press, 2014. Provides a great comprehensive treatments of self-knowledge in Aquinas's thought. She argues for a view of self-awareness that contrasts with Robert Pasnau in“Knowing the Mind” in Thomas Aquinas on Human Nature, 330–360. Cambridge: Cambridge University Press, 2002. Further good reading on the topic of self-awareness and self-cognition are found in Martin, Christopher. J. “Self-Knowledge and Cognitive Ascent: Thomas Aquinas and Peter Olivi on the KK-Thesis.” in Forming the Mind: Essays on the Internal Senses and the Mind/Body Problem from Avicenna to the Medical Enlightenment, edited by H. Lagerlund, 93–108. Dordrecht: Springer, 2007. And in German “Thomas von Aquin:" in Zugänge zum Selbst: Innere Erfahrung in Spätmittelalter und Früher Neuzeit, Münster: Achendorff 2015. 37-60

(2) Kriegl, Uriah "Consciousness and Self-Consciousness" Monist 87 no. 2, 182-205 (2004)

(3) Dan Zahavi has written extensively on this topic, but a good overview can be found in his co-authored piece with Uriah Kriegel. Zahavi, Dan; Kriegel, Uriah. “For-me-ness: what it is and what it is not” in Philosophy of Mind and Phenomenology, 36-53. Routledge, 2015.

(4) The term "quidditative self-knowledge" comes from Cory (2014)

(5) Summa Theologiae I q87 a1 "But as regards the second kind of knowledge, the mere presence of the mind does not suffice, and there is further required a careful and subtle inquiry. Hence many are ignorant of the soul's nature, and many have erred about it."

(6) De Veritate 10.9; Summa Theologiae I q87 a2

(7) I use Robert Pasnau's translation. A Commentary on Aristotle’s De Anima.  Yale University Press, 1999. See page 6

(8) "...we would rather know a little about the highest things, the things more worthy of special honor, even if we know it topically (i.e., with probability), than know much, with certainty, about things less lofty in status. For the former has its lofty status through itself and its substance, whereas the latter takes this status from its type and quality"ibid

(9) Cassam, Quassim. Self-Knowledge for Humans. First edition. Oxford University Press, 2014

A Thomistic Account of Quidditative Self-Knowledge's Value

Coming soon...

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