It’s Sunday. I’m sitting outside a café in Place de La Sorbonne in the snow. The terrace heaters barely make an impact on the cold and I’m wrapped up in scarf, coat, fur hat and fingerless gloves. I’m reading a book and drinking a tiny, repellently bitter coffee. I’m outside in the freezing cold so I can smoke. In 2010, even in Paris, you can’t smoke inside, which makes the slogan of the Gauloises cigarette brand — Liberté toujours — sound ironic and desperate. I don’t — didn’t — smoke Gauloises. I’m smoking Golden Virginia, rolling thin, stringy cigarettes to save money. The book I’m reading while smoking is a self-help book. On how to quit smoking. So far, so good.

Smoking, Francophilia, doctoral study: some of my more egregious youthful follies. I was in Paris as a foreign student at the École Normale Supérieure on Rue d’Ulm, just up the boulevard from Place de la Sorbonne. I was writing my PhD on Plato, learning French, going to dozens of seminars and talks on ancient philosophy. I remember Jonathan Barnes, dressed as an 18th century flaneur, lecturing on Plato’s Theaetetus in grammatically perfect French, with his upper-class English accent. It was surreal. I think he still smokes a pipe.

Smoking crops up as an example in ancient philosophy scholarship all over the place. In the ’70s and ’80s, smoking was a standard counter-example to the Socratic paradox that “No one who knows an action is evil does it willingly.” When philosopher and beret-enthusiast Nick Denyer asked me how I quit, I joked that I simply realized that smoking is an evil, then I ceased to do it willingly.

I did eventually quit smoking. And I did it more or less in the way that I quipped to Nick. Everyone knows that smoking is, all things considered, bad, really bad, and not worth having in your life. What’s hard is believing that smoking is bad, in the face of nicotine cravings and the propaganda of tobacco companies (Liberté toujours!). Eventually, I developed tricks to help with that. For example, I never say — or think silently to myself — that I “gave up” smoking. That implies that smoking is an indulgence. Something positive. Crush that implication. Another example: bring yourself to realize that one cigarette is not just one — it’s the first one in a chain that will lead to the last. I used to imagine that each cigarette was a loaded gun pointed at my head with a 50–50 chance of killing me. This is what you might call the “cognitive hack” approach to breaking a habit.

Habits good, bad, and moral

For us, smoking is an exemplary bad habit — harmful, expensive, and repulsive. Of course, there are other paradigm bad habits — nail-biting, coffee-drinking, listening to Ed Sheeran. But bad habits tend to be bad because of their effects. Smoking is bad because it kills. Coffee-drinking because it encourages hipster coffee shops. Ed Sheeran — well take your pick: atomization of society, Brexit, Trump, cyber-bullying, global warming, North Korean nuclearization, resurgent Russian aggression.

In other words, modern bad habits, even addictions, are bad, but not morally bad. The enlightened don’t moralize about smoking, drinking, or listening to Ed Sheeran, even if we think that it’s better not to. But in the context of ancient ethics, habits are crucial for ethical theory and tend to be morally charged. Anger and lust are paradigm examples of bad ancient habits. For one thing, having good habits conditions good ethical theory (Aristotle, NE 1095b4–6). For another, habits ground moral virtues. Getting a virtue is a matter of getting into the habit of acting and thinking in a certain way in certain circumstances. A persistent person habitually continues on in the face of adversity. So any philosopher interested in helping us become more moral will be interested in how we gain and lose habits.

Epictetus

In the first century of our era, Stoic freed-slave Epictetus was just such a philosopher. Epictetus draws on a long, and highly technical, philosophical tradition, Stoicism, to try to help his students lead better lives. In a time when contemporary academic philosophy offers little to those seeking advice on living, Epictetus has become a darling self-improvement gurus. There are even modern movements aiming to revive Stoicism as a way of life. But Epictetus doesn’t just offer off-the-cuff life advice. His views about habits are based in some fairly technical, and puzzling, ancient modal and temporal logic.

Logic is the theory of how we reason (or ought to reason). Modal logic concerns reasoning about possibility (how things could be), necessity (how things must be) and impossibility (how things cannot be). Temporal logic concerns reasoning about the past and future. Here’s an example of combining modal and temporal logic: I am, in fact, not French, but I could have been; if I had been French, I would have smoked Gauloises. Aristotle gets the credit for inventing logic — the mighty syllogistic — and for inventing modal logic. But Aristotle was not the only ancient interested in modal logic — Epictetus’ Stoic school was full of cunning modal and temporal logicians.

In his Discourses, Epictetus tells us what it takes to get a habit: “Every habit … is maintained and increased by the corresponding actions: the habit of walking by walking, the habit of running by running.” Plausibly, a habit is a disposition to act in a certain way that is acquired by repeatedly acting in that way. I become a walker by repeatedly walking; I become a smoker by repeatedly smoking. But a disposition is a property I have even when I’m not actually acting in a certain way. I’m a smoker — I have the disposition to smoke — even if I’m not smoking a cigarette right now.

Epictetus also tells us how to break a habit:

If then you wish not to be of an angry temper, do not feed the habit: throw nothing on it which will increase it: at first keep quiet, and count the days on which you have not been angry…. I used to be in passion every day; now every other day; then every third, then every fourth … For the habit at first begins to be weakened, and then is completely destroyed.

To lose a habit, like smoking, simply refrain from smoking. This doesn’t seem right at all. Philosophically, being a smoker and actively smoking come apart. I was a smoker between cigarettes — just because I increase the interval between cigarettes, it does not mean I’m less of a smoker. This point cuts the other way too. I might repeatedly perform an action, without having the disposition to act in that way. I might repeatedly force cigarettes down, but never be disposed to. There is more to having a habit then repeatedly acting in a certain way; but there is also less.

A more down to earth objection, of course, is that quitting smoking isn’t as easy as Epictetus makes out! There is more to losing a habit than simply not acting in a certain way: I also need to lose the disposition to act in that way. We need some means, some tool to help us learn to lose our bad habit. “Cognitive hacking” is one. Epictetus suggests another: seek out moral exemplars. These are people who have mastered themselves, and their habits. Epictetus mentions Socrates, a famous moral examplar, resisting his habitual lust for Alcibiades. The tool we should use to quit smoking is: look at ex-smokers and copy them.

The problem with this advice is that it is not obvious who I should copy. A smoker between cigarettes looks just the same as an ex-smoker, or a non-smoker. Of course, it’s true that I’ll find it harder to quit smoking if I spend my time with people who are chain-smoking. But it’s not obvious that the reverse will obtain. After all, what do ex-smokers do that non-smokers don’t? Both simply don’t smoke. But that just leaves me with the same advice as before: quit smoking by not smoking. Which isn’t how it works, as any smoker, or ex-smoker will tell you. Philosophers would put the point by saying that I do not have epistemic access to the dispositions: I do not know whether you are a non-smoker, an ex-smoker, or a smoker between cigarettes. If I don’t know that, how can modeling my behavior on yours help me quit?

By now we can see that there is a gap between having a habit and repeatedly performing the corresponding action. Epictetus ignores that gap, and by ignoring it, he doesn’t speak to our modern concerns about how to lose our bad habits.

Epictetus’ lesson in ancient modal logic

So far, Epictetus’ fans from the self-help community have him right. Unlike abstract analytic philosophy, Epictetus theorizes the grit of leading a life. Sure, I’ve criticized his advice as philosophically and practically unworkable; but at least he offers some. However, immediately after this discussion of habit, Epictetus changes gear and launches into a discussion of ancient modal and temporal logic. More about modal and temporal logic! You’re probably already off, hastening the apocalypse by looking for videos of Ed Sheeran.

Specifically, Epictetus records what’s known as the “Master Argument.” Diodorus Cronus, a distant intellectual ancestor of Epictetus, posed the Master Argument in the third century BCE. More of a puzzle than a straightforward argument, the Master shows that these three claims about modality and time are inconsistent:

(i) past truths are necessary. In other words, the past is fixed: you can’t change the past, not matter how much you want to (I smoked for years; I can’t go back and change that now!).

(ii) possible truths don’t follow the impossible. For example, if it is impossible for me to train every day, then I couldn’t be an Olympic athlete.

(iii) there is a possible truth which neither is true nor will be. In other words, there are some mere possibilities: things that are possible, but which will never actually happen (such as me becoming an Olympic athlete).

It’s not obvious why this triad is inconsistent. Philosophers still disagree. Even Epictetus admits he doesn’t understand the argument! Which invites the question: if Epictetus is concerned with Stoic philosophy as a way of life, why is he taking us on this tedious foray into Wonderland?

I think it is because he wants us to recognize that the Master puzzle gives us a way to close the gap between what we can do and what we in fact do. Let me explain.

Epictetus records that his intellectual ancestor, Diodorus Cronus, rejected (iii). (iii) says that there are mere possibilities: possibilities that don’t hold now and never will. In some sense, I can become an Olympic athlete. But being an Olympian is a mere possibility for me because I smoked too much: I’m not an Olympian now and actually never will be.

Rejecting (iii) is to assert that are no mere possibilities. Anything I can do, I actually do, either now or in the future. To say that I can become an Olympic athlete just means that I’m an Olympian now or will be in the future. This conception of possibility seems strange — but I won’t hunt down the strangeness here. What is key is that Diodorus solved the Master puzzle by closing the gap between what I can do and what I actually do. And it was precisely this gap which Epictetus ignored in his account of habit.

Epictetus’ attempt to change our habits was limited because he ignored the gap between having a disposition to smoke and actually smoking. Diodorus’ solves the Master Argument by closing the gap between what I can do and what I actually do. But if there is no gap between what I can do, and what I actually do, Epictetus’ account of habit starts to make sense. To lose the habit of smoking, just don’t smoke! Habit and action don’t come apart. There is nothing to being a smoker, except actually smoking; there is nothing to being a non-smoker, except actually not smoking. Moreover, I can find loads of great exemplars for not smoking: just find someone who is not smoking and copy them not smoking. What Epictetus says about ancient modal logic makes sense of his ideas about habit.

But this is more than a philosophical response — it is therapeutic too. Epictetus juxtaposes this technical argument from ancient modal logic with his discussion of habit. Why? Answer: to tell us to cultivate a Diodorean idea of habit. Diodorus, remember, closes the gap between what I can do and what I actually do. For Diodorus, I can lose a habit, if, but only if, I stop actually acting in that way. I can stop being a smoker, if, but only if, I stop actually smoking.

Even if, like Epictetus, we cannot solve the Master argument, just accepting what Diodorus would say about habit may well help you to change your habits. After all, if Diodorus is right, becoming a non-smoker is simple — just stop putting cigarettes in your mouth and stop lighting them. There is no disposition to smoke over and above the regular action of smoking. Don’t say to yourself “I’m a smoker.” That implies that you have a disposition to smoke which is hard to shift. Rather, when not smoking, say “I’m a non-smoker,” because there is nothing more to being a non-smoker than not smoking.

That, I think, links technical ideas from proto-Stoic modal logic with the nitty-gritty reality of leading a life. The technical side of Stoicism doesn’t just philosophically underpin the moral theory and practical advice Epictetus dishes out. Working through technical material helps us psychologically, with the life-project of losing bad habits and acquiring good ones. Accepting Diodorean ideas about modality is a kind of cognitive hack. Just like looking at exemplars or purging the phrase “giving up” from my vocabulary.

Studying ancient modal logic can help to free you. It does not offer the freedom to act any way you like, but rather the freedom from evils — bad habits that steal your money, time and peace of mind. Habits that corrupt your body, character and virtue. Freedom from those, for a Stoic, is truly liberté toujours.

Disclaimer: this article contains affiliate links

Matthew Duncombe is an Assistant Professor in Philosophy at the University of Nottingham in the UK. He studied philosophy and classics at the University of Cambridge and has taught at the University of Groningen and Durham University. He quit smoking in 2010.