Full Idea
It will be ridiculous if our student knows the definition of the circle and of the divine sphere itself, but cannot recognize the human sphere and these our circles, used in housebuilding.
Gist of Idea
It is absurd to define a circle, but not be able to recognise a real one
Source
Plato (Philebus [c.354 BCE], 62a)
Book Reference
Plato: 'Complete Works', ed/tr. Cooper,John M. [Hackett 1997], p.451
A Reaction
This is the equivalent of being able to recite numbers, but not to count objects. It also resembles Molyneux's question (to Locke), of whether recognition by one sense entails recognition by others. Nice (and a bit anti-platonist!).
Related Idea
Idea 3938 Geometry is originally perceived by senses, and so is not purely intellectual [Berkeley]