Arendt drew the concept from the Greek polis, but she insisted the public realm was not limited to ancient city-states. Any gathering of plural persons engaged in action and speech constitutes one; the New England town meeting, the revolutionary council, the civil-rights movement all qualify. The question is whether the conditions for such gathering exist.
The concept operates as both description and norm. Descriptively, the public realm is what exists whenever plural persons encounter one another. Normatively, it is the condition for human flourishing in Arendt's sense: only in the public realm can persons become fully who they are, because only there can they be seen by others.
The AI moment threatens the public realm in a specific way. When the builder partners with an AI, she produces outputs that can be distributed to an audience, but her production occurs in private, without the presence of other persons. The screen is not a public realm. The machine does not witness; it processes. The distinction matters because what emerges from private dialogue with an accommodating tool is different in kind from what emerges from public encounter with irreducibly different beings.
The Arendt simulation treats this as a civilizational challenge. Individual builders cannot reconstitute the public realm by themselves; the conditions require institutional supports — spaces, times, and norms that bring plural persons into encounter. The silent middle of the AI transition is partly a symptom of public-realm erosion: the absence of a space where nuanced perspectives can appear and be heard.
Arendt developed the concept across The Human Condition (1958) and Between Past and Future (1961), drawing on Greek political thought (particularly Aristotle's Politics) and on her engagement with contemporary democratic theory. Her worry about the decline of the public realm animated much of her late work, including On Revolution (1963) and Crises of the Republic (1972).
Space of appearance. The public realm is where actors reveal who they are to others through deed and word.
Common world. It is also the shared durable reality of institutions and practices that persists across generations.
Not geographical. It comes into being wherever plural persons gather to act and speak; it dissolves when they disperse.
Private dialogue is not public. The builder's screen, however productive, is not a public realm; the machine does not witness.