Full Idea
People often think they are practising dialectic when they are practising eristic; this is because of their inability to conduct the enquiry by dividing the subject-matter into its various aspects.
Clarification
'Eristic' is argument as a contest, but 'dialectic' is co-operation in pursuit of truth
Gist of Idea
People often merely practice eristic instead of dialectic, because they don't analyse the subject-matter
Source
Plato (The Republic [c.371 BCE], 454a)
Book Reference
Plato: 'Republic', ed/tr. Waterfield,Robin [OUP 1993], p.165