Full Idea
Nobody attributes happiness to a slave, unless he also attributes to him a life of his own.
Gist of Idea
Slaves can't be happy, because they lack freedom
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1177a08)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.328
A Reaction
Give them freedom then! In 'Politics' he allows a degree of friendship between masters and slaves, and recognises that not all slaves are stupid.