[What is a friend?:] A single soul inhabiting two bodies.

This definition of friendship is traditionally attributed to Aristotle in later anthologies and commonplace books, often presented as a stand‑alone maxim (“What is a friend? A single soul dwelling in two bodies”). However, modern scholarship on Aristotle’s surviving works has difficulty locating this exact wording in the Greek texts. Aristotle does treat friendship (philia) at length—especially in the Nicomachean Ethics (Books VIII–IX) and Eudemian Ethics—where he analyzes kinds of friendship and the idea that a friend is “another self.” The “one soul in two bodies” phrasing appears to be a later paraphrase or a spurious attribution that crystallizes Aristotelian themes rather than a securely traceable sentence from his extant corpus.

The aphorism presents friendship as a profound unity: two distinct persons share one moral and emotional life. Read alongside Aristotle’s ethics, it evokes the idea that the best friendship is grounded in virtue, where each friend recognizes the other as “another self” and wills the other’s good for the other’s sake. The “single soul” image stresses harmony of character, shared aims, and mutual understanding—friendship not as mere companionship or advantage, but as a form of ethical kinship. It also implies that genuine friendship enlarges the self: one’s identity and flourishing become intertwined with another’s.

1) "Friendship is one soul in two bodies." 2) "A friend is a second self." 3) "A friend is another self."