Full Idea
When appearance and measure conflict…it is the best part of the mind which accepts measurements and calculations, and the part which opposes them, therefore, must be a low-grade part of the mind.
Gist of Idea
If theory and practice conflict, the best part of the mind accepts theory, so the other part is of lower grade
Source
Plato (The Republic [c.371 BCE], 603a)
Book Reference
Plato: 'Republic', ed/tr. Waterfield,Robin [OUP 1993], p.355