I used to be and (to an extent) still am interested in stoicism as a life philosophy.
To start with, I think the core difference is this: Buddhism was founded by someone who personified the ideals of the system. Stoicism was not. Stoicism does not have a “Buddha” or a “Sage” to take refuge in, and it doesn’t really have a 3rd or 4th Noble Truth.
That may just sound like a negative, but it makes stoic texts much more approachable. Meditations is a book by a guy who’s really sad about his dead children and stressed out about his job trying to talk himself through life’s challenges. The Enchiridion and Discourses of Epictetus are records of a formerly enslaved man, crippled by his former enslaver, trying to talk sense into the elite youth of Rome. The Suttas are a fully enlightened being’s attempt to lead those with little dust in their eyes to understand profoundly subtle truths.
A lot of what you find in a modern Dharma talk aimed at a lay audience simply isn’t found directly in the Suttas. I may have missed a passage, but having read through all of what was available on Suttacentral about a year ago, I do not recall a single sutta where the buddha recommended something like, “meditate for a half an hour in the morning and before bed and that will help you deal with the annoying people in public places.” That’s not to say such messages are inauthentic or anything like that, just that these ideas need to be drawn out of the text and arrived at by synthesis. Multiple Stoics directly address that specific problem more-or-less that way.
By “more-or-less” I mean that stoic meditation isn’t exactly the same thing as prevalent modern western meditation. But I’d argue it’s closer than the samadhi of the suttas - because the suttas mostly talk about high levels of practice that are not being taught by your HR department in a half-hour lunch and learn. I think the most famous stoic meditation technique is premeditatio malorum, forethought of bad things, where you visualize bad things that might occur in your day, as well as how you might respond to them. I don’t think this really has an analog in Buddhism, but stoicism has something like an analog for the Brahmaviharas and recollection of virtue. There is a practice where at the end of the day you reflect on your virtues throughout the day, and a contemplation of the cosmos or view from above that provides more practical guidance on how your supposed to go from being an ordinary self-centered person to contemplate wider and wider circles of beings until your are encompassing the whole cosmos with equanimous care. The meditation practices described in stoic philosophy are relatively straightforward, and good for someone who wants to be less cranky on the bus or with their spouse. There’s just no reason to believe they can ever lead to any standard of perfection.
From the perspective of someone who isn’t aiming quite so high, the biggest problem with Stoicism is that it is pro-killing. Zeno of Citium, the founder, is said to have suddenly and violently smashed his own head open as an intentional response to having accidentally broken his big toe. Marcus Aurelius casually mentions killing Christians just to make a point about their “false courage”. Seneca, in his On Anger talks repeatedly about how stoicism and emotional regulation makes you a better killer, and of course he and Marcus were responsible for the deaths of multitudes through their roles in the Empire.
Generally speaking, Stoicism lacks any concrete moral rules. The four Stoic virtues of justice, wisdom, courage, and temperance, are all psychological. The Stoics are normally fairly moral persons - they don’t encourage murder or wanton theft or anything like that. Both Marcus and Seneca express some regret or hesitancy about violent aspects of the Empire. But they don’t recognize or teach anything like the precepts or right livelihood. Epictetus, even having been enslaved, is not recorded as having ever called out the trade in human beings as fundamentally wrong, and himself purchased at least one slave.
Of course, I don’t think most modern Stoics are pro-slavery or killers. Similarly, many westerners who are casually interested in Buddhism may not take the precepts very seriously. This disinterest in the difference becomes even more extreme when it comes to physics.
Stoics had some buck-wild, demonstrably false beliefs about the world. They thought the equator was literally always on fire, as one example. Their whole system is fairly complex, and not of interest to many people, but they thought of it as being very closely tied in to their ethics. Two key points here are the idea of divine providence and Zeus-given free will.
The Stoics believed that we lived in a rational universe, not just in the sense that you can write equations describing how leverage works, but the same way you might describe humans as “rational beings”. They identified this cosmic mind with Zeus / Jupiter, and thought it was the best. So everything, from the precise way a tree falls in the forest with nobody around to hear it, or someone savagely beating you until your leg is so broken it will never recover, is part of a greater good. This is not part of Buddhism. There is no sense, for example, that all of the people who acted badly and prompted vinaya rules to be written were part of some greater plan by a cosmic intelligence. No, when Devadatta caused a schism in the Sangha and worked with Ajasattu on that parricidal plot, that was just two men doing bad things.
Superficially contradictory, the Stoics also believed in a radical sort of free will, where the part of your soul that makes choices (the hêgemonikon) is literally impervious to outside effects. It could move itself in response to outside phenomenon, but nothing outside itself (not even Zeus) could cause it to move. Meaning, for instance, that it was equally possible to develop sagacity as a prisoner starving in a dungeon as a king feasting in a palace (and presumably as a mendicant eating between dawn and noon). No historical figure claimed to be a perfect sage, and it’s unlikely a modern stoic is taking the pursuit too seriously, but I think that if you did this would be a major stumbling block. Buddhism, first off, anticipates and soundly rejects this view of self in relation to the aggregate of choices, identifying choices as being neither “me” nor “mine”, rather being caused and conditioned. Second, Buddhism is far more open to the idea of material circumstances mattering to practice. The catalyst for the Buddha’s awakening was ceasing his self-mortification and eating moderately to fuel the body for the practice of Jhana, and even as an awakened being he, for instance, left the monastery to meditate in the grove with the bull elephant when loud arguing overwhelmed the monastic community.
Overall, I think Stoicism and Buddhism are very similar and compatible at the level the average modern westerner is likely to engage with them. If you’re just looking for psychological tips and tricks to get through the day with greater ease and less stress, they’re very close and quite compatible. But if you start to get serious about Buddhism and engage in the noble eightfold path and read the stoics more thoroughly, you’ll discover a lot of Stoic ideas you have to reject.
