Stoicism is an ancient Greco-Roman philosophy (Zeno of Citium (334-262 BC), Epictetus (50-135 AD), Seneca (4 BC-65 AD)).
Stoicism was highly influential in the Roman Empire (the "Last Good Emperor" Marcus Aurelius and his meditations).
It continued to be influential throughout the Middle Ages (Thomas Aquinas) and the Enlightenment (Descartes, Spinoza), and has recently witnessed
a resurgence of interest.
Massimo Pigliucci, a contemporary proponent of Stoicism and an author of a number of books on Stoic philosophy and its application in 'real life',
highlights 'two pillars' of Stoicism:
the four cardinal virtues and the dichotomy of control.
The four cardinal virtues
Wisdom (phronesis in Greek, prudentia in Latin)
A sense of what is good (for us, for others, in general) and worthwhile to pursue, and what is bad and ought not to be pursued or encouraged.
Courage (andreia in Greek, fortitudo in Latin)
Resistance to fear and motivation to persist in the face of obstacles as well as moral courage, including the courage to speak up.
Justice (dikaiosyne in Greek, iustitia in Latin)
Acting fairly, treating others with kindness and consideration, abiding by laws.
Temperance (sophrosyne in Greek, temperantia in Latin
Best described as moderation, golden mean. Doing everything in the right measure: not too much, not too little.
Dichotomy of Control
The dichotomy of control refers to focusing our actions and thoughts on what we can control and not worrying or focusing on what we cannot control.
In the words of Epictetus:
"Some things are within our power, while others are not.
Within our power are opinion, motivation, desire, and, in a word, whatever is of our own doing;
not within our power are our body, our property, reputation, and, in a word, whatever is not of our doing."
In practice, this means we should focus on our efforts, on doing the best we can, following the cardinal virtues.
TED talk by Massimo Pigliucci
Another talk by Massimo Pigliucci
Modern Stoicism - courses, resources
Stanford Encyclopedia of Philosophy article
Encyclopedia Britannica overview article
Books on Stoicism