The transition from an animal's primary self-preservation to a cosmopolitan concern for all humanity is a central challenge in Stoic ethics. The mechanism for this is oikeiosis, an innate process of appropriation. In the Hieroclean model, this isn't a sudden shift but a developmental expansion. It begins with the appropriation of one's own constitution and progressively extends to encompass others. The entire structure rests on the initial impulse, or hormē towards what is one's own, a process that begins with the very first moment of perception.

At its root, oikeiosis is grounded in an organism's continuous self-perception, or synaisthēsis. From birth, an animal is not a blank slate reacting to external stimuli. It possesses an immediate awareness of its own body, its parts, and its functionality. This is the primary object of appropriation. The animal feels its constitution as its own, as something to be preserved and valued for its own sake. This initial self-appropriation isn't a rational conclusion but a pre-rational, instinctual reality. It is the bedrock upon which all subsequent ethical development is built. The impulse (hormē) to maintain this constitution is the first and most fundamental expression of nature.

This primary state, however, is not static. The very mechanism that establishes self-love becomes the engine for social extension. The most immediate example is the care for offspring. For Hierocles, a parent's concern for their child is not a separate, altruistic impulse. Instead, the child is perceived as an external extension of the parent's own being. The child's constitution is appropriated and internalized, falling under the purview of the parent's own self-preservation impulse.

The transition to social oikeiosis occurs when the hormetic drive begins to appropriate things external to the physical body. This is not a transfer of affection but an expansion of the self. The value previously attached only to one's own constitution is now projected onto others, starting with those closest to us. Hierocles famously illustrated this with his model of concentric circles, which provides a powerful visual for understanding the structure of our social duties. We naturally feel a strong connection to those in the innermost circles, like our immediate family. The ethical task of the Stoic is to actively work to draw the outer circles inward.

This internalization is the core mechanism of social oikeiosis. When we see a relative, we are not simply observing an external object. We are perceiving something that is, in a real sense, a part of us. The sense of belonging (synaisthēsis) extends beyond our skin. The rational being recognizes the shared nature of humanity and understands that this process of appropriation should logically extend to all other rational beings. Thus, the initial impulse for self-preservation becomes the foundation for cosmopolitan justice.

Ultimately, the movement from primary to social oikeiosis is not a replacement of one concern for another. It is a continual expansion of the definition of 'self.' The initial, animalistic attachment to one's own body provides the motive force. Reason then provides the direction, guiding that force to its logical conclusion: the appropriation of the entire human community as one's own.