While reading and researching Musonius Rufus for this post, I came across an interesting article by Richard Valantasis entitled “Musonius Rufus and Roman Ascetical Theory.” Valantasis is a scholar and Episcopal priest who has also written The Making of the Self: Ancient and Modern Asceticism and appears to be one of the most prominent living writers on ascetical studies. He focuses on Musonius Rufus’ “ascetical theory” and asks why scholars have downplayed this aspect of Musonius’ thought: “Although Musonius provides the earliest extant ascetical theory, few scholars have noticed, explored, or explained his theory in relationship to his philosophy.”  Is there a difference between the Stoic practices that Musonius propounded and asceticism? It’s hard to argue there is no connection when the root of asceticism, askesis, is the word for the “exercises,” or practical enactment of ethical principles, that Musonius urges his followers to undertake on their path to virtue.
In his sixth Discourse, usually translated “On Training” but which Valantasis refers to as “On Asceticism” (which certainly bolsters his thesis), Musonius writes that philosophy, although a discipline and skill like the practice of medicine, is actually more difficult that other areas of study because those
who enter the other professions have not had their souls corrupted beforehand and have not learned the opposite of what they are going to be taught, but the ones who start out to study philosophy have been born and reared in an environment filled with corruption and evil and therefore turn to virtue in such a state that they need a longer and more thorough training.
Musonius believed humans’ depravity was not innate, but learned through socialization. As Valantasis puts it, “Negative socialization hardens into bad habits that impede philosophical progress by habitually interpreting hardship as evil, pleasure as good, death as misfortune, life as a blessing, monetary benefaction as loss, and monetary gifts as gain.” 
Musonius argues that the philosopher in training must therefore habituate himself “not to love pleasure, not to avoid hardship, not to be infatuated with living, not to fear death, and in the case of goods or money not to place receiving above giving.”
As Valantasis writes, the “contrary ascetical discipline . . . establishes the values of the true philosopher.”  Musonius’ virtue is the product of philosophical theory strengthened by practice; neither theory nor practice is sufficient on its own.
How does one fully understand and embody justice, courage, prudence, and wisdom? The same way you get to Carnegie Hall. Valantasis again: “The practices associated with a particular virtue give the virtue substance and authenticity.”  To be just, practice not being selfish or greedy; to be courageous, practice confronting fearful situations head-on, and so on.
According to Valantasis, it is more appropriate to identify Musonius, as well as Epictetus and Marcus Aurelius, with their asceticism than with their philosophical schools: “Musonius Rufus leads the way in this movement, providing both a complete ascetical system central to his philosophy, and a set of applications of these principles in the daily life of his followers.” 
But why haven’t others picked up on this characterization of his work that seems obvious? John Sellars in his Stoicism does not mention the word asceticism, although he does discuss askesis, Musonius’ Discourse 6, and his assertion that philosophers have to try harder than anyone else at their art because they have been surrounded by corruption their whole lives–the opposite of virtue. 
Is it a question of the secularization of modern-day Stoicism? I associate asceticism with religion; although religion is not a necessary element, my impression is that the ascetic renounces earthly desires to achieve a state of nearness to his God. This is from a website focusing on modern issues in Christianity: “Ascetics renounce worldly pleasures that distract from spiritual growth and enlightenment and live a life of abstinence, austerity and extreme self-denial.”
Modern Stoicism, or at least the strain that is more prevalent nowadays, is not focused on God but instead on mortal concerns. Stoicism is seen as a way not to rise above or diminish quotidian events, but to strengthen one’s spirit to face them. I see Musonius’ exercises as a way to fortify myself and develop willpower, courage, and so on as if they were muscles in my body.
I see the ascetic’s renunciation almost as a denial of the reality of this world in favor of the imminent perfection of the afterlife. Yet according to the website referenced above, “In many cases, the ascetic practices self-denial in order to earn God’s favor or somehow purge himself from sin. This shows a misunderstanding of grace; no amount of austerity can earn salvation or merit God’s love (Ephesians 2:8-9).”
As an atheist I am not focused on an afterlife; I need tools–virtue muscles–to face the difficulties of this life. I think it is telling that Musonius believes that humans are born with the capacity for nobility and virtue, but that we have been corrupted by society starting from when we were children. It would seem that an ascetic, on the other hand, is renouncing the fact of human-ness as a whole by acting as though ignoring or suppressing innate human desires, instead of developing tools to manage them, is the only path to virtue.
 Richard Valantasis, “Musonius Rufus and Roman Ascetical Theory,” Greek, Roman, and Byzantine Studies 40 (1999), 207-31 at 210.
 Ibid. at 216.
 Ibid. at 217.
 Ibid. at 230.
 See John Sellars, Stoicism (University of California Press 2006) at 33, 45-6.