Zeno of Citium, a Cypriot philosopher who had gone to Athens at about the age of twenty-three, had been impressed both by the Cynics and the Megarian logicians.

Zeno teaches moral obligation, self-control, and harmony with nature.

Advocating a life that "follows reason"—that is free from passion, dignified, and self-respecting—he founds the austere ethical doctrine of Stoicism, based on the notion that one is either a good person in every way, or, if one succumbs to any shortcomings, is totally without virtue.

Zeno teaches that the human soul is not complex but is truly only reason; the remainder—ambition, appetite, fear—is in no way part of the self and should therefore be eliminated.

An atomic theory offered by Epicurus is similar to one formulated by Democritus.

Epicurus teaches that the universe’s creation came about by chance, that the physical things we sense are real and that we may trust our senses.

As there is no sensation after death, we need not fear it.

As the soul—composed, according to Epicurus, of the body’s finest particles—cannot exist independently of the body, pleasure is therefore the highest pursuit, with intellectual pleasure a greater good than sensual pleasures.

Epicurus also teaches that natural selection favors only those who are fit to survive.