त्रयाणामेव चैवमुपन्यासः प्रश्नश्च ॥ ६ ॥
trayāṇāmeva caivamupanyāsaḥ praśnaśca || 6 ||
trayāṇām—Of three; eva—only; ca—and; evaṃ—thus; upanyāsaḥ—introduction; praśnaḥ—question; na—and;
6. And thus the question and elucidation with reference to three only (of which the Pradhana is not one) (is consistent).
In the Katha Upanishad Nachiketas asks Yama three questions only, viz. about the fire (sacrifice), the individual soul, and the Supreme Self. The Pradhana is not mentioned. So we cannot expect Yama to go out of his way and treat of the Pradhana, which has not been inquired into.