यदा वै मनुतेऽथ विजानाति नामत्वा विजानाति मत्वैव विजानाति मतिस्त्वेव विजिज्ञासितव्येति मतिं भगवो विजिज्ञास इति ॥ ७.१८.१ ॥
In plain words
"When a man thinks, then he understands; one who does not think does not understand. Only one who thinks understands. But one must seek to understand thinking." "Sir, I seek to understand thinking."
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
यदा वै मनुत इति । मतिः मननं तर्कः ॥
In plain words
As for the expression 'when indeed one reflects'—mati means pondering and logical reasoning.
Close to the Sanskrit
'When indeed he reflects'—mati is pondering, reasoning.