Kathavatthusutta 3.2

3.2

Sacāyaṃ, bhikkhave, puggalo pañhaṃ puṭṭho samāno ṭhānāṭhāne na saṇṭhāti parikappe na saṇṭhāti aññātavāde na saṇṭhāti paṭipadāya na saṇṭhāti, evaṃ santāyaṃ, bhikkhave, puggalo akaccho hoti.

When an individual is asked a question, if they’re not consistent about what their position is and what it isn’t; about what they propose; about speaking from what they know; and about the appropriate procedure, then that individual is not competent to hold a discussion.