[Four-fold examination] All the worldly objects can be divided into two categories, truth (or existence) and false (or non-existence). There are four methods of examination- scriptures or texts (words of persons with superior intellect, or sages), direct perception (direct observance), inference and reasoning.
आप्तास्तावत्- रजस्तमोभ्यां निर्मुक्तास्तपोज्ञानबलेन ये| येषां त्रिकालममलं ज्ञानमव्याहतं सदा ||१८||
[Authoritative sages] Those who are enlightened and knowledgeable are absolutely free from rajas and tamas (psychological doshas). By virtue of this, they possess knowledge of trikala (past, present and future) and are known as authorities (aptas).
hey are also known as the wise and the enlightened (vibuddha) persons. Their words are considered absolute truth without any doubt. As they are free from rajas and tamas, how could they tell lie?
आत्मेन्द्रियमनोर्थानां सन्निकर्षात् प्रवर्तते| व्यक्ता तदात्वे या बुद्धिः प्रत्यक्षं स निरुच्यते ||२०||
[Knowledge by Direct Perception] Knowledge gained by the proximity of soul, sense faculties, mind with the object of study or observation is known as perception or direct observation (pratyaksha).