Symposium · Ethics · Pl. 5Aristotle · 384–322 BC
A Friend Is a Second Self
Too much space for a nice-to-have
Modern ethics usually treats friendship as a pleasant extra, not a core moral topic. Aristotle disagreed sharply enough to devote roughly a fifth of the Nicomachean Ethics to it, arguing that even a person who had every other good thing, wealth, health, virtue, would still be missing something essential to a complete human life without genuine friends. He opens the discussion by observing that nobody would choose to live without friends even if he had all other goods, and that friendship is what holds cities together, so that lawgivers care more about it than about justice. Where there is friendship, he says, there is no need of justice. Where there is only justice, something is still missing.
The world it came from
Aristotle wrote about friendship in Athens in the 330s BC, teaching at the Lyceum he had founded after returning from Macedon. The Greek word is philia, and it is wider than the English: it covers the bond between parents and children, between fellow citizens, between business partners, and between the men who fought beside each other in the phalanx. A Greek city was small enough that these bonds were its politics. Aristotle had also lived the topic. He had spent twenty years in Plato's Academy among people who argued for a living, and he left it when Plato's nephew was chosen to lead it instead of him. Books VIII and IX of the Ethics read like a man who had thought carefully about which of his friendships had been real.
The idea
The best kind of friendship, friendship of virtue, is not built on usefulness or pleasure but on each person wishing the other well for the other's own sake. In this friendship, the good man relates to his friend as to himself, since a friend is, in Aristotle's phrase, a second self: someone whose flourishing you care about the way you care about your own. Such friendships are rare because good people are rare, and slow because trust of that depth takes time; you cannot know a person, Aristotle says, until you have eaten the proverbial measure of salt together. They are also lasting, because they rest on what the friends are, not on what they happen to want from each other this year.
How the reasoning runs
Start with what a good person feels toward himself: he wishes himself good things for his own sake, wants to go on living, enjoys his own company, and shares his own griefs and joys. Second, these are exactly the marks by which we recognize friendship toward others. So the good person's relation to his friend is the same relation, extended. Third, a person can only see himself with difficulty. But we can see a friend, and a friend of virtue is a person like us. So contemplating a friend's good actions is a way of contemplating our own life, which is the activity happiness consists in. Fourth, therefore the happy person needs friends, not as comfort but as the mirror in which his own goodness becomes visible to him.
Seen in life
Sort your phone. There is the colleague you message when you need a favor, and who messages you for the same reason; when one of you changes jobs, the thread will go quiet. There is the friend who is a joy at a party and unreachable at a funeral. Aristotle would call both of those friendships, and real ones, and lesser. Then there is the one person whose good news you feel as your own, who you would call first if you had done something shameful, whose flourishing matters to you. That is the second self. Aristotle's claim is not that you should have more of those. It is that a life without one is missing something no other good can replace.
Why it matters
This makes friendship a genuine extension of ethical life rather than a break from it. If a friend really is a second self, then watching a friend act well is a way of witnessing goodness in action, and helping a friend flourish becomes, in a real sense, an extension of caring for your own flourishing rather than a separate, secondary concern. It also answers a hard question about self-sufficiency. The Stoics and Epicureans both wanted a happiness that could survive the loss of everyone. Aristotle refused that trade. The good life, on his account, is one that can be damaged by the death of a friend, and a theory that removes that vulnerability has removed the friend as well.
“The good man is to his friend as to himself, friend being but a name for a second Self.”
From the source
Aristotle states the claim directly: “The good man is to his friend as to himself, friend being but a name for a second Self.” Because your own existence is worth choosing, he argues, so too, in a similar way, is your true friend's. The sentence comes from Book IX, chapter nine, where Aristotle asks whether a happy person will need friends at all, given that the happy person is supposed to lack nothing. His answer is that happiness is an activity, not a possession, and that we can perceive a friend's activity more easily than our own. A friend is chosen, he says, the way life itself is chosen, and to perceive a friend is to perceive, in a way, oneself.
The pushback
Isn't this an impossibly demanding standard, since most people's actual friendships are built on convenience, shared interests, or simple enjoyment rather than this deep mutual concern for the other's own good? Aristotle would agree; he explicitly ranks friendships of pleasure and utility as real but lesser, common, and often short-lived, reserving the second-self description for the rarer, deeper kind alone. A harder objection is that the phrase gives the game away. If I love my friend as a second self, I love him for what he shares with me, and the argument that I need him as a mirror makes him an instrument of my own self-perception. That looks less like love of another person than like a sophisticated form of self-love.
The reply
Aristotle saw the self-love objection coming and met it head-on: the good person, he says, should be a lover of self, because what he loves in himself is the rational and virtuous part, and loving that part in another is the same love, not a rival to it. The friend is not a mirror in the sense of a tool; he is a person whose good is wished for its own sake, which is the definition Aristotle started from. Whether that fully removes the worry is doubtful. The argument for needing friends does lean on what the friend provides to the happy person's self-awareness, and a reader who wants friendship to be entirely about the other will find Aristotle's account warmer than his argument.
Where it went next
Cicero turned the books into a Latin dialogue, De Amicitia, in 44 BC, and through him the second self reached the Middle Ages. Aelred of Rievaulx wrote Spiritual Friendship for monks in the twelfth century, and Aquinas defined charity itself as a kind of friendship with God. Montaigne's essay on friendship, written after the death of Étienne de La Boétie, gives the phrase its most famous echo: asked why he loved him, Montaigne could only say, because it was he, because it was I. C. S. Lewis defended friendship as the least natural and most spiritual of the loves in 1960. The modern research on loneliness and health, which finds that isolation shortens lives, is the empirical footnote to Aristotle's claim that nobody would choose all other goods without it.
Where this leads
Hell is other people offers a starkly different picture of what another person's presence does to you, turning Aristotle's warm, mutual second self into something closer to a threat, a gaze that fixes and judges rather than one that shares in your own flourishing. Eudaimonia is the frame this beat belongs inside. Aristotle's argument that the happy person needs friends only makes sense once you know that happiness, for him, is activity rather than a feeling, because it is the friend's activity that a person can watch and share. Read the two Aristotle beats together, then Sartre, and the question sharpens. Is another person's eye the thing that completes you, or the thing you can never escape?