Aristotle: Nicomachean Ethics
How ought we do find the mean?
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Aristotle seems pretty pessimistic about the possibility of being a virtuous person by discursive reasoning; for, as he says, we often disagree about what is too much or too little. Rather than discursive reasoning, then, Aristotle seems to think that being virtuous is primarily about experience, working out boundaries in practical scenarios.
Aristotle, Nichomachean Ethics, Book II