Full Idea
A human being's good is existing in accordance with reason, while what is bad for a human being is whatever is contrary to reason.
Gist of Idea
For humans good is accordance with reason, and bad is contrary to reason
Source
Thomas Aquinas (Summa Theologicae [1265], Ia IIae.Q18.5c), quoted by Kretzmann/Stump - Aquinas, Thomas 13
Book Reference
'Shorter Routledge Encyclopaedia of Philosophy', ed/tr. Craig,Edward [Routledge 2005], p.43
A Reaction
For anyone who thought Kant invented the idea that morality derives from reason. This idea of Aquinas is a fairly precise echo of the stoic view (which influenced Kant). Is there a circularity? Is it irrational because bad, or bad because irrational?