Full Idea
In our reasoning we need a clear view of the ability to divide a genus into species, observing the natural joints, not mangling any of the parts, like an unskilful butcher.
Gist of Idea
Reasoning needs to cut nature accurately at the joints
Source
Plato (Phaedrus [c.368 BCE], 265d)
Book Reference
Plato: 'Phaedrus and Letters VII and VIII', ed/tr. Hamilton,Walter [Penguin 1973], p.82
A Reaction
In modern times this Platonic idea has become the standard metaphor for realism. I endorse it. I think nature has joints, and we should hunt for them. There are natural sets. The joints may exist in abstract concepts, as well as in objects.
Related Ideas
Idea 13775 We only succeed in cutting if we use appropriate tools, not if we approach it randomly [Plato]
Idea 3123 Science is in the business of carving nature at the joints [Segal]
Idea 3303 For anti-realists there are no natural distinctions between objects [Dummett, by Benardete,JA]