Full Idea
Nothing that is contrary to nature is fine.
Clarification
'Fine' is the Greek word 'kalon', which also translates as 'beautiful'
Gist of Idea
Nothing contrary to nature is beautiful
Source
Aristotle (Politics [c.332 BCE], 1325b09)
Book Reference
Aristotle: 'Politics', ed/tr. Sinclair,T.A. /Saunders,T. [Penguin 1992], p.400
A Reaction
This seems a rather conservative view, since it rules out submarines, mountaineering and heart transplants.. It depends what we count as 'natural'.