Nature, as we say, does nothing without some purpose; and for the purpose of making man a political animal she has endowed him alone among the animals with the power of reasoned speech. Speech is something different from voice, which is possessed by other animals also and used by them to express pain or pleasure; for the natural powers of some animals do indeed enable them both to feel pleasure and pain and to communicate these to each other. Speech on the other hand serves to indicate what is useful and what is harmful, and so also what is right and what is wrong. For the real difference between man and other animals is that humans alone have perception of good and evil, right and wrong, just and unjust. And it is the sharing of a common view in these matters that makes a household [oika] or a city [polis].
Aristotle. Politics. (quoted in Giorgio Agamben. Infancy and History: The Destruction of Experience. trans. Liz Heron. NY: Verso, 1993.)