In Sanskrit, knowledge is called pramā, the knower of such valid knowledge is called pramātā, and the means by which it is validly known is called pramāna.

Pramāna can also mean “proof,” “evidence,” or “authority.”

Keśava Miśra gives the following definitions in his Tarkabhāṣā 1.2-3:

"Pramā-karaṇam pramāṇam, atra pramāṇaṁ lakṣyaṁ, pramākaraṇaṁ lakṣaṇam"

The karaṇā or the most essential cause of attaining proper understanding, proper cognition, valid knowledge (pramā) is called pramāna. Therefore, if pramāna is proper then knowledge will be proper and if pramāna is improper then obviously the knowledge will be improper.

Different schools of Indian philosophy and theology accept different pramāṇas as valid. According to Jīva Gosvāmī, there are a total of ten pramāṇas, or means of valid knowledge, which he lists in his Sarva-saṁvādinī commentary.

Each school recognizes a certain number of these as valid independent means, and either reject the rest or subsumes them under the accepted pramāṇas. Each school presents arguments to support its opinion.

These ten traditional pramāṇas, with the three most important listed first, are as follows:

1. Pratyakṣa, perception.

2. Anumāna, inference.

3. Śabda, revealed sound-knowledge.

4. Ārṣa, the statements of an authoritative sage, ṛṣi, or deva.

5. Upamāna, comparison.

6. Arthāpatti, presumption.

7. Anupalabdhi, non-cognition of being, or cognition of the absence of being.

8. Sambhava, inclusion.

9. Aitihya, tradition.

10. Ceṣṭā, gesture.

It's important to note that although there are ten pramāṇas, the root pramāṇa is scripture alone, whose nature is sentences devoid of the faults of misapprehension, illusion, willful-deception, and the faulty senses.

For most people, knowledge received through the senses is the very definition of direct, or pratyakṣa jñāna. For example, when we taste an apple with our own tongue, we say that we directly experienced it – the apple was aparokṣa or immediate to us (the words “immediate knowledge” mean knowledge unobstructed from us by anything else). Likewise with seeing and so on.

Indeed, this is also the definition of pratyakṣa in Nyāya which goes like this:

indriya-sannikarṣajanyam jñānaṁ pratyakṣaṁ - The perceptual knowledge resulting from contact between a sense and its sense object is pratyakṣa jñāna.

The followers of Śankarācārya insist that śabda or words can also give aparokṣa jñāna or direct knowledge of external or internal objects within our perceptual range. This is a key precept of Advaita-vāda, and Śrī Jīva Gosvāmī also accepts it.

When a sense organ comes in contact with a perceivable object under favorable conditions, and provided the sense faculty is internally linked with the mind, then knowledge of the perceived object arises in the mind. This is known as perception.

Perception is of two types — external and internal. An external perception occurs when we acquire knowledge of quantifiable objects through the external senses. In an internal perception we acquire knowledge directly through the mind, as when we perceive emotions such as pain, pleasure, love, and hate.

In Gītā 15.7, Śrī Kṛṣṇa lists the mind as the sixth sense (manaḥ-ṣaṣṭhānīndriyāṇi).

Perception can be a means to either valid or invalid knowledge. But only those sense perceptions that lead to valid knowledge should be considered as pramāṇa.

Because of the defect of inadvertence (pramāda), and because our senses are prone to delusion (bhrama) and limitation (karaṇāpāṭava), pratyakṣa is not a consistently reliable means of acquiring valid knowledge.

Besides these defects, the scope of pratyakṣa is limited only to the present, since perceptions by definition cannot be of past or future events. Moreover, it is limited only to external or internal phenomena.

To explain something the general procedure is to refer to shastra and then give an example to illustrate it.

Generally apasiddhānta is an outcome of misinterpreting śāstra and then giving an example to illustrate the misinterpretation.

Sometimes apasiddhānta is just based upon an example, like the famous example of Ramakrishna Paramahamsa that Realization of the Absolute is like a salt doll entering into an ocean. Once it enters, there is no more doll, only the ocean. The example is very good but there is no shastra to support it.

No and yes. No, because he is not Hari. He is Hari’s devotee. Yes, because he passes on Hari’s teachings in the parampara.

Because he does the function of Hari, he is considered Hari.

Śrī Rūpa Gosvāmī cites verse SB 11.3.21 in the Bhakti-rasāmṛta-sindhu to describe both the guru and the disciple. Gopāla Bhaṭṭa Gosvāmī also cites this same verse in his book Hari Bhakti Vilāsa in a similar context, and Sanātana Gosvāmī elaborates on it further in his commentary.

The verse is as follows –

tasmād guruṁ prapadyeta jijñāsuḥ śreya uttamam
śābde pare ca niṣṇātaṁ brahmaṇy upaśamāśrayam

Therefore, one desirous of knowing the ultimate welfare should resort to a teacher who is well versed in scripture, has realized the absolute reality, and thus is fully peaceful.

The qualifications of the teacher then are as follows. He/she is

• śābde niṣṇātaṁ – expert in the knowledge of sastra.
  The word niṣṇātaṁ means that a person is drenched in knowledge, like one is drenched when taking a shower.
• pare niṣṇātaṁ – has realization of it.
  The guru is also drenched (niṣṇātaṁ) in experience of parabrahman, and not only knowledge.
• Practices it in his/her own life.

To recognize a genuine teacher is not easy. The śābde niṣṇātaṁ part may be easier to determine. One can inquire about

1. Whether the guru spent a significant amount of time with their guru (several years). This is recommended by Gopāla Bhaṭṭa Gosvāmī in the Hari Bhakti Vilāsa (pp. 32 onwards).
2. Whether the guru took systematic training in the different darśanas.
3. Whether the guru is well-versed in Sanskrit, the language of the scriptures.

These are some basic standards that should be met. Of course, it is not possible to discern the pare niṣṇātaṁ part for any disciple.

Śrīla Jīva Gosvāmī states that, when the word "Kṛṣṇa" is uttered in a mantra, as in the Hare Kṛṣṇa mahā-mantra, this sound attracts the attention of Śrī Kṛṣṇa Himself the very moment the first syllable is vibrated. This is so because the name “Kṛṣṇa” is identical with the person Kṛṣṇa, the Supreme Person.

This is verified by the experience of many realized devotees who attained perfection by chanting the Hare Kṛṣṇa mantra.

The Viṣṇudūtas stated this to the Yamadūtas:

nāma-vyāharaṇaṁ viṣṇor yatas tad viṣayā matiḥ

When a person chants the name of Śrī Viṣṇu, the Lord’s attention is drawn toward the chanter. (SB 6.2.10)

Although the Name is all-powerful, it does not reveal its power to a person who is not free of offense, niraparādha. There are ten major offenses against the Name and one of them is śruti-śāstra-nindanam – criticizing śruti and smṛti. Criticizing is not just a verbal thing. It also includes not respecting what is stated in them. Accepting a guru is one of the important instruction of the śastra. In Bhakti-rasāmṛta-sindhu, Śrī Rūpa Gosvāmi lists accepting guru as the primary step on the path of sādhanā bhakti which leads to prema. So if one chants the Name without accepting a guru avoiding offenses then the Name will guide such a person to a guru. This is the verdict of Śri Viśvanatha Cakravartī Ṭhākura in his commentary on the story of Ajāmila in Śrīmad-Bhāgavata.

Learn more: No Bhakti Without Surrender.