Definition
Oikeiosis is a Greek term, roughly meaning appropriation or familiarization, that the Stoics used to explain how care develops. Every creature begins with an instinctive concern for its own survival and well-being — it treats itself as its own.
In rational beings this self-concern matures into something wider. As reason develops, a person comes to recognize others as akin to themselves, and the circle of what feels like one's own expands.
Why it matters
How it works
The Stoics pictured concern as a series of concentric circles: self, family, friends, fellow citizens, and finally all of humanity. The moral task is to draw the outer circles inward, treating distant people with something closer to the care we naturally extend to those nearest us.
This expansion is not sentimental; it follows from reason recognizing a shared nature. Because every human possesses the same rational spark, each is genuinely a relative. Living according to nature therefore includes acting justly toward all, since to be rational is also to be social.