यदा वै विजानात्यथ सत्यं वदति नाविजानन्सत्यं वदति विजानन्नेव सत्यं वदति विज्ञानं त्वेव विजिज्ञासितव्यमिति विज्ञानं भगवो विजिज्ञास इति ॥ ७.१७.१ ॥
In plain words
"When a man understands, then he speaks the truth; one who does not understand does not speak the truth. Only one who understands speaks the truth. But one must seek to understand understanding." "Sir, I seek to understand understanding."
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
यदा वै सत्यं परमार्थतः विजानाति- इदं परमार्थतः सत्यमिति, ततः अनृतं विकारजातं वाचारम्भणं हित्वा सर्वविकारावस्थं सदैवेकं सत्यमिति तदेव अथ वदति यद्व- दति । ननु विकारोऽपि सत्यमेव, 'नामरूपे सत्यं ताभ्या- मयं प्राणश्छन्नः' 'प्राणा वै सत्यं तेषामेष सत्यम्' इति श्रु- त्यन्तरात् । सत्यमुक्तं सत्यत्वं श्रुत्यन्तरे विकारस्य, न तु पर- मार्थोपेक्षमुक्तम् । किं तर्हि ? इन्द्रियविषयाविषयत्वापेक्षं सच्च त्यच्चेति सत्यमित्युक्तं तद्वारेण च परमार्थसत्यस्योपलब्धिर्वि- वक्षितेति । 'प्राणा वै सत्यं तेषामेष सत्यम्' इति च उक्तम् । इहापि तदिष्टमेव । इह तु प्राणविषयात्परमार्थसत्यविज्ञाना- भिमानादुत्थाप्य नारदं यत्सदेव सत्यं परमार्थतो भूमा- ख्यम्, तद्विज्ञापयिष्यामीति एष विशेषतो विवक्षितोऽर्थः । नाविजानन्सत्यं वदति ; यस्त्वविजानन्वदति सोऽग्न्यादिश- ब्देनाग्न्यादीन्परमार्थसद्रूपान्मन्यमानो वदति ; न तु ते रूप- त्रयव्यतिरेकेण परमार्थतः सन्ति । तथा तान्यपि रूपाणि सदपेक्षया नैव सन्तीत्यतो नाविजानन्सत्यं वदति । विजा- नन्नेव सत्यं वदति । न च तत्सत्यविज्ञानमविजिज्ञासितम- प्रार्थितं ज्ञायत इत्याह-विज्ञानं त्वेव विजिज्ञासितव्य- मिति । यद्येवम्, विज्ञानं भगवो विजिज्ञासे इति । एवं सत्यादीनां च उत्तरोत्तराणां करोत्यन्तानां पूर्वपूर्वहेतुत्वं व्याख्येयम् ॥
In plain words
When someone truly knows what is true in the highest sense, knowing 'this is the truth in the highest sense', then he leaves behind the untrue, the whole host of modifications, which is only a matter of words, and knows that the existent alone, which abides as every modification, is the one truth; and then whatever he says, he speaks that truth. But surely modification is true as well, as other śrutis say: 'name and form are true; this prāṇa is covered by them', and 'the prāṇas are truth, and he is their truth'. True, another śruti does call modification true; but it does not say so with the highest truth in view. What, then? The elements are called true, as sat and tyat, with a view to whether or not they are objects of the senses, and the point is that through them the truth in the highest sense is reached. And it is said: 'the prāṇas are truth, and he is their truth'. That is accepted here too. But what is specially meant here is this: Sanatkumāra wants to raise Nārada out of his belief that in knowing prāṇa he knows the highest truth, and to make known to him what alone is the truth in the highest sense, the existent, which is called bhūman. Someone who does not know does not speak truth. Someone who speaks without knowing uses the words 'fire' and the rest, and takes fire and the rest to exist in the highest sense; yet apart from the three forms they do not exist in the highest sense. And those forms in turn do not exist at all beside the existent; so someone who does not know does not speak truth. Only someone who knows speaks truth. And that knowledge of truth does not come unless it is sought and prayed for; so he says: 'but it is understanding that you should seek to understand'. If that is so, 'Lord, I seek to understand understanding'. In the same way, for truth and the rest, each later one, all the way down to 'doing', is to be explained as the cause of the one before it.
Close to the Sanskrit
When indeed one knows truth in the highest sense, [thus:] 'this is true in the highest sense', then, leaving the untrue, the host of modifications, a mere matter of words, [and knowing] 'the existent alone, abiding as all modifications, is the one truth', he then speaks that very [truth], whatever he speaks. Surely modification too is true, according to other śrutis: 'name and form are true; by them this prāṇa is covered', 'the prāṇas are truth, and he is their truth'. True, in another śruti the truth of modification is stated; but it is not stated with reference to the highest truth. What then? With reference to being or not being an object of the senses, [the elements] are called true as sat and tyat, and through that the apprehension of the truth in the highest sense is intended. And it is said: 'the prāṇas are truth, and he is their truth'. Here too that is accepted. But here the meaning specially intended is this: raising Nārada from his conceit of knowing the highest truth in [knowing] prāṇa, [Sanatkumāra thinks] 'I shall make known what, the existent alone, is the truth in the highest sense, called bhūman'. One who does not know does not speak truth. But one who speaks without knowing speaks taking fire and the rest, [named] by the words 'fire' and the rest, to be existent in the highest sense; yet they do not exist in the highest sense apart from the three forms. So too those forms themselves do not exist at all in relation to the existent; hence one who does not know does not speak truth. Only one who knows speaks truth. And that knowledge of truth is not known without being sought to be known, without being prayed for; so he says: 'but it is understanding that should be sought to be understood'. If so, 'Lord, I seek to understand understanding'. In this way, for truth and the rest, each later one, down to 'doing', is to be explained as the cause of each earlier one.