The author discusses Aquinas's treatment of Aristotle and investigates the treatment of Aristotelian justice in his commentary on Book 5 of the Nicomachean Ethics and the way he incorporates this treatment into his systematic writings. This is an interesting test case because in his commentary Aquinas undoubtedly misinterprets at least two of Aristotle's key contentions in ways that make Aristotle look more Thomistic. Aquinas includes in his interpretation material that is foreign to Aristotle. Aquinas uses his partly erroneous and expanded interpretation as the basis for his own treatment of justice in the Summa theologiae. So, if there is a case to be made that Aquinas is un-Aristotelian, anti-Aristotelian, or subverter of Aristotelianism, we might expect to find it in his treatment of Aristotle on justice. Aristotle's ethics provides Aquinas with what appears to be the best system natural reason has produced.