For the Stoics, virtue is the only true good, while vice is the only true evil. Everything else—health, wealth, reputation, illness, poverty—falls into the category of indifferents, neither good nor bad in themselves, though Stoics distinguish preferred indifferents (such as health) from dispreferred ones (such as sickness). Virtue consists in aligning thought and action with reason and nature: a single, unified excellence expressed through four cardinal forms: wisdom, courage, justice, and temperance. These virtues are not separate skills but four facets of one rational disposition, each flowing from the others. Wisdom is the ability to discern what is genuinely good from what is genuinely bad and to act accordingly. Courage means doing what is right despite fear, pain, or risk. Justice involves treating others fairly and recognizing that all human beings share a common rational nature. Temperance is self-mastery, the moderation of desires and emotions so that reason remains in control.
The Stoic claim that virtue is both necessary and sufficient for happiness distinguishes the school from other virtue ethics, particularly Aristotle's. Aristotle saw virtue as a mean between extremes and treated external goods like friendship and moderate wealth as important for flourishing. The Stoics held instead that the wise person remains happy regardless of external fortune, since externals do not touch the soul's virtue. Fortune's wheel may lift and cast down, but the person of wisdom stands unshaken. "Wealth consists not in having great possessions," Epictetus remarked, "but in having few wants." The fully virtuous sage stands as an ideal rarely, if ever, realized in practice, so Stoics prefer to speak of the proficient—those making genuine progress along the path of wisdom. What matters is the pursuit of virtue, not perfection itself.
Stoicism thus treats philosophy as a way of life requiring daily practice, the disciplined effort the Greeks called askesis or epitedeuma. Progress, not perfection, is the realistic aim: the path of the wise is a lifetime of cultivation rather than a completed state. Stoic ethics is also distinct from asceticism: Stoics do not reject pleasures outright but refuse to attach themselves to externals that lie outside their control. Equally, Stoicism stands opposed to hedonism—the view that pleasure is the highest good—and to rival schools like Epicureanism, which sought tranquility through the careful management of pleasure rather than through virtue.