Bolotin, David, Plato's Dialogue on Friendship: An Interpretation of the Lysis with a New Translation, Ithaca: Cornell University Press, 1979.

Excerpt:

If we wish to find philosophic discussions of friendship, we are almost compelled to turn to the writings of classical antiquity. The question of friendship was an important one for ancient thinkers. Yet in modern times, philosophers have rarely given it an explicit place in their moral teaching or in their treatment of social and political life. Friendship does not seem to fit into any of the modern systems of thought.

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