Full Idea
Socrates' rule of "say only what you believe"….excluded debate on unasserted premises, thereby distinguishing Socratic from Zenonian and earlier dialectics.
Clarification
'Zenonian' refers to Zeno of Elea, follower of Parmenides, who was famous for his paradoxes, such as the 'Achilles'
Gist of Idea
In Socratic dialogue you must say what you believe, so unasserted premises are not debated
Source
comment on Socrates (reports of career [c.420 BCE]) by Gregory Vlastos - Socrates: Ironist and Moral Philosopher p.14
Book Reference
Vlastos,Gregory: 'Socrates: Ironist and Moral Philosopher' [CUP 1992], p.14