Full Idea
The whole essence of propriety is quite certainly consistency.
Clarification
'Propriety' is behaving well
Gist of Idea
The essence of propriety is consistency
Source
M. Tullius Cicero (On Duties ('De Officiis') [c.44 BCE], 1.110)
Book Reference
'The Hellenistic Philosophers:Vol.1 translations', ed/tr. Long,A. /Sedley,D. [CUP 1987], p.424
A Reaction
This seems to me the key intuition on which Kant built his deontological ethical theory. However, opponents say the consistency requires principles, and these are the enemies of truly good human behaviour, which involves Aristotle's 'particulars'.