Recent years have witnessed a surging interest in the science of habits among researchers and laypeople alike, the latter demonstrated by the intense popularity of James Clear’s Atomic Habits (2018) with over ten million copies sold. Previous popular forays into habits, such as Stephen R. Covey’s The 7 Habits of Highly Effective People (1989), tended to take the format of a wealthy, athletic, or otherwise successful person doling out advice on what habits, routines, and practices had worked in their own lives and the lives of their successful friends. While these approaches certainly had merit, little attention was paid to whether scientific support for the advice dispensed could be found. In contrast, Clear’s book brims with research on the best ways—according to psychology, biology, and other branches of science—to make new habits stick all while breaking bad habits.
Another author very interested in habits was medieval philosopher and theologian Thomas Aquinas (AD 1225–1274), whose Summa Theologiae mentioned the Latin word habitus and its variants hundreds of times and included a dedicated section on the matter. The venerable Doctor of the Church viewed the cultivation of positive habiti (and the destruction of negative ones) as essential to Christian life. Christians are, after all, encouraged to develop good habits such as church attendance and daily prayer while shunning vices like lust and gluttony, so they ought to be very interested in both the science and theology of habits. In what ways has modern-day research vindicated Aquinas’ teachings on habitus? This is the question Ezra Sullivan seeks to answer in Habits & Holiness: Ethics, Theology, and Biopsychology. Or as Wojciech Giertych explains in his foreword to the book, Sullivan “not only presents the teaching of Aquinas on the habitus, but also correlates this with contemporary neuroscience and biological psychology.” In other words, Habits & Holiness is “an example of the value of a theologically-inspired metaphysical synthesis for modern empirical science” (xv).
The book is divided into three parts, along with an introduction and a brief conclusion. In the introduction, Sullivan discusses empirical studies of habit and the philosophy of habit, contextualizes Aquinas’ attention to habit within the Summa Theologiae, and addresses an objection by Servais Pinckaers on whether our modern concept of habits and habitus in the thought of Aquinas are relatable. In addressing habitus and habits, Sullivan discusses the extent to which habits are automated, their relationship to choice and free will, and the moral consequences of our view of habits as related to automation.
Part 1, “Subterranean Habits,” consists of three chapters. The first of these chapters discusses the habits and dispositions humanity possesses by nature of being human and how these differ from the “instinctual behaviors” of animals. The second discusses dispositions bequeathed to humans by race, genetics, DNA, gender, and body chemistry. Curiously, Aquinas believed in and utilized a theory of four “temperaments” with different personality traits (Sanguine, Choleric, Phlegmatic, and Melancholic), not unlike popular modern-day personality tools like the Enneagram or Myers-Briggs, although Sullivan does not mention these and cites more academic personality studies instead. The third chapter examines how habits are acquired through experience, sometimes involuntarily in our youth or even in utero: “An enormous number of empirical studies can confirm many of Thomas’s points, and they go beyond his position, definitely showing that humans can acquire nonvoluntary actional dispositions, beginning in utero” (121). These chapters lay the bedrock for consideration of largely involuntary dispositions and habits.
Part 2, “Human, Inhuman, and Divine Habits,” contains five chapters representing the largest section of the book. In these chapters, Sullivan looks more closely at the role of freedom in habituation (chapter 4), the accumulation of positive habits and especially justice, fortitude, and temperance (chapter 5), the acquisition or possession of negative habits like original sin (chapter 6), the presence of grace in the cultivation of good habits (chapter 7), and the role of divinely infused habits, especially faith, hope, and charity (chapter 8). It is in these chapters that Sullivan provides the bulk of his habit attenuation theories (or, rather, Aquinas’) and the ways in which they are backed by biology, psychology, and philosophy. The final part, “Hacking Your Habits,” consists of just two chapters and focuses on practical means of eliminating sinister habits while pursuing benevolent ones.
Habits & Holiness is an impressive volume. The book represents an ambitious intersection of many different disciplines, touching on classical philosophy, historical theology, ethics, genetics, neuroscience, biopsychology, and others, drawing in an expansive list of researchers, thinkers, and premodern voices alongside that of Aquinas. Protestants who wish to benefit from it will have to modify its distinctly Catholic advice and utilization in places—see its use of penance (505), intercession of the saints (518), and most significantly, its departure from “Calvinistic theologies that posit a complete depravity of humanity on account of original and personal sin” (458)—but this should be expected given the Catholicism of its author, its publisher, and its pre-Reformation subject. There is much wisdom on display here, such as in its advice to “overcome our desire to avoid knowing our defects” (525).
It is difficult to offer criticism of the book, because any perceived deficiencies may merely be deficiencies in Aquinas’ medieval thought, but I will offer that a more critical reading of Aquinas was in order. I counted only one place where Sullivan notes Aquinas got his science wrong, and then he still credited him as being “right in general” (126); are there really so few areas where Aquinas’ science is wrong? In some places, Sullivan is probably being too generous in crediting Aquinas with getting his science correct. For example, popular personality type metrics like the Enneagram and the MBTI are widely derided by psychologists and neuroscientists for being pseudo-scientific. Can we really say Aquinas’ belief in Sanguine / Choleric / Phlegmatic / Melancholic types is supported by modern science because personality type studies exist? And while Aquinas got many things right, it seems there were many tricks to habit attenuation that he was not aware of, such as habit stacking and environment design. One will not come away with a clear picture of how to implement these techniques from reading Sullivan.
More significantly, the book contains precious little discussion of two of the most significant habits for Christians to develop: prayer and Bible reading. Prayer is mentioned in a few places (e.g., 133, 180), although mostly in passing; Bible reading as a habit or discipline is not mentioned. This is no doubt because it was not a discipline that was expected of medieval Christians, given the lack of literacy among the general population and the absence of Bible translations in the vernacular; habits such as mass attendance would have anticipated this critical modern-day habit. Again, though, a corrective or supplement to Aquinas would have been appropriate here. Ultimately, the book supplies few practical suggestions for habits that would develop holiness. As a minor quibble, I noted close to thirty typographical or syntactical errors, which became rather distracting and seems like a lot for a book this size.
In conclusion, Habits & Holiness should be of interest to students of Thomism specifically as well as to Christians looking to expand their theological understanding of habit attenuation. It may function as an updated, modernized reader for one aspect of the Summa Theologiae for those who find reading the actual Summa too daunting, and Christians of all kinds who can handle lengthy discussion of the theological aspects of habit attenuation will learn much from Sullivan’s insights. In general, the world would benefit from more books like this that explore the extent to which past theologians are now vindicated by research.