Full Idea
Since there is a Soul which reasons upon the right and good - for reasoning is an enquiry into the rightness and goodness of this rather than that - there must exist some pemanent Right, the source and foundation of this reasoning in our soul.
Gist of Idea
The Soul reasons about the Right, so there must be some permanent Right about which it reasons
Source
Plotinus (The Enneads [c.245], 5.1.11)
Book Reference
Plotinus: 'The Enneads', ed/tr. Mackenna,Stephen [Penguin 1991], p.359
A Reaction
This is pretty close the Kant's concept of 'the moral order within me', and Plotinus even sees it as rational. Presumably this right is 'permanent' because the revelatlons of reason about it are necessary truths.