The greatest epithet of a teacher is Ācārya. In course of writing on several sūtra (sutra; formulae) of Pāṇini (Panini), Patañjali (Patanjali), the author of Mahābhāṣya(Mahabhashya) has mentioned four types of teachers — Ācārya (Acharya), Upādhyāya (Upadhyaya), Śikṣaka (Sikshaka) and Guru. Amongst these, Guru is the most common epithet, and Ācārya is the highest. Patañjali himself paid homage to the creator of Vyākaraṇa (Vyakarana; Grammar), addressing him as Ācārya. While explaining the rules of grammar, he does not mention the name of the sūtrakāra (sutrakara, creator of the formula) but with great respect, repeatedly referred to him as Ācārya — “ācārya prvṛttirjñāpayati“. On the other hand, in Bhāgavatapurāṇa(Bhagavatapurana) God himself established himself in the form of Ācārya , and said, –the brahmacārī (brahmachari; one who performs brahmacharya) śiṣya (sishya; disciple)should know him to be a manifestation of myself, and he will never show disrespect to Ācārya. He will not discover faults among the virtues of Ācārya, considering him as merely human. All deities reside in the teacher, in the form of Ācārya —
ācāryyaṁ māṁ vijānīyānnāmanyeta karhicit
na martyavuddhyāsūyeta sarvadevamayo guruḥ.
In Mahābhārata (Mahabharata), the name of Droṇa has come repeatedly as the greatest Ācārya, and with the very utterance of the term Ācārya, there is an obvious reference to Droṇacārya. In Śāntiparva (Santiparva) of Mahābhārata, we have another explanation of the term Ācārya, but it is worthy of a different explanation. To establish the importance of the parents, references to Ācārya and Upādhyāya have come. It is said that one Ācārya is equal to ten Śrotriya Brāhmaṇa(s), one Upādhyāya is equal to ten Ācārya(s), one father is equal to ten Upādhyāya(s), and the one who can assimilate the importance of ten fathers, is a mother.
daśācāryān upādhyāyaḥ upādhyāyān pitā daśa
pitṛn daśa tu mātaikā sarvām vā pṛthivīmapi.
In this śloka, the honour of the mother is established so highly, that the hierarchy of Ācārya and Guru also gets reversed. Elsewhere in Mahābhārata we don’t find any śloka containing a comparative status of the Upādhyāya and the Ācārya, and there is no point of comparison with Guru or teacher. Wherever the term Ācārya has been mentioned, his highest honour becomes evident according to the concerned context and environment.
In this śloka, the honour of the Upādhyāya has been highly established, but there is no mention of the term Ācārya, which should have been there. Here the term Guru is the common recognition on one who imparts knowledge. Those who dishonour the guru, even after gaining knowledge from him, are sinners — this common sense was part of the social ethics at that time–
vidyāṃ śrutvā ye guruṃ nādriyante
pratyāsannā manasā karmaṇā vā.
teṣāṃ pāpaṃ bhrūṇahatyāviśiṣṭaṃ
nānyastebhyaḥ pāpakṛdasti loke.
Along with this honour generally due to a guru, the special honour due to the Ācārya has been uttered here with more emphasis. Especially the term Ācārya has been identified with a jāti, and thus the culture of the entire community of Indian society, in those days, comes to be glorified in Mahābhārata–
ācāryaviśiṣṭā yā jātiḥ sā divyā sājarāmarā.
That is, the jāti (jati) which is controlled by the Ācārya(s), is associated with the gods, it is without age or decay; that community is immortal. However, in the same chapter of Mahābhārata, the importance of Upādhyāya is held higher than the Ācārya. It is said that the behaviour and manners which please an Upādhyāya, are also the mean of worshipping the Absolute Divinity (Parama Brahman). One Upādhyāya is more venerable than the parents–
yena prīnātyupādhyāyaṃ tena syād brahma
mātṛtaḥ pitṛtaścaiva tasmāt pūjyatamo guruḥ.
After declaring that ten Upādhyāya(s) are equal in respect to one father, and ten fathers are equal to one mother, Mahābhārata actually brings the father, the mother and the Upādhyāya at the same level, and then announces that– one who dishonours one’s father, mother and Upādhyāya by word or action, is a great sinner–
upādhyāyaṃ pitaraṃ mātarañca
ye’bhidruhyante manasā karmaṇā vā
teṣāṃ pāpa bhrūṇahatyāviśiṣṭaṃ
tasmānnānyaḥ pāpakṛdanti loke.
In this śloka, the highest honour due to the Upādhyāya has been established, but the term Ācārya has not been mentioned, which should have been.
At the time of Mahābhārata itself, the hierarchy of Ācārya, Upādhyāya and the like — became established. In this regard, it can be considered that the importance of Upādhyāya, as stated earlier, has declined to some extent. In the Dharmasūtra of Gautama, it is said that Ācārya is the greatest of all teachers, since he imparts Vedavidya (knowledge of Veda). Drawing on this statement, in Vaśiṣṭha Dharmasūtra (Vasishtha Dharmasutra) it is said that the Ācārya is to be recognised as father, since he imparts the knowledge of Veda(s), or in other words, the father is the first teacher of Veda, so he is Ācārya–
vedapradānāt pitetyācāryam ācakṣate.
One who trains the brahmacārī (brahmacari, practitioner of celibacy) disciple in the knowledge of Veda, after his Upanayana, is called Ācārya. And one who cannot impart the full knowdge of Veda, but teaches partially, or such Vedaṅga(s) as Śikṣā, Kalpa, Vyākaraṇa and the like, is called the Upādhyāya.
It is to be noted that after the definition of Upādhyāya and Aācarya– at least ten chapters after this, Vaśiṣṭha Dharmasūtra says, like Mahābhārata, that an Ācārya is ten times more respected than an Upādhyāya, one father is equal to an Ācārya, and the glory of a mother is equal to one thousand fathers. This śloka of Vaśiṣṭha Dharmasūtra is exactly similar to the one in Manusaṃhitā–
upādhyāya daśācārya ācāryānāṃ śataṃ pitā
piturdaśataṃ mātā gauravenātiricyate.
Though this śloka is the highest recognition of the grace of a mother, it also establishes that the importance of Ācārya is far greater than Upādhyāya, and that the Ācārya is the greatest among all teachers.
While defining the term Ācārya, Āpastamva Dharmasūtra has beautifully said that — the person from whose teachings the disciple picks and collects (cayana and āharaṇa) dharma-niyama, is an Ācārya–
yasmāddharmānācinoti sa ācāryaḥ.
In Yājñavalka Smṛti, there is a distinction between Guru and Ācārya, as it is said– One who imparts advices on the several saṃkāra(s), beginning from Niṣeka to Śmaśana (that is, from the foetal state to the time of death and funeral), is Guru, in fact he is the father. And the one who imparts to the disciple, after his Upanayana, the knowledge of the four Veda(s), is Ācārya.
sa guruḥ yaḥ kriyā kṛtvā vedamasmai prayacchati
upanīya dadadvedam ācāryaḥ sa udāhṛtaḥ.
In Viṣṇudharmasūtra the statement is almost similar, but there the Ācārya is addressed to as Atiguru, in parallel to the father and mother-
trayaḥ puruṣasya atiguravo bhavanti.
mātā pitā ācāryaśca.
In Manusaṃhitā, the status of an Ācārya becomes the most clearly evident. Manu has clearly stated that after performing the Upanayana-ceremony of the disciple, the teacher who trains him in the knowledge of ṣaḍṅga (six-part) Vedanta, comprising of Śikṣā, Kalpa and the like, along with the mystical knowledge of Brahman through Upaniṣad and the whole of Veda.
And the one who teaches one portion of Veda, that is, the mantra-part of Veda or the Brāhmaṇ-part, or the six Vedāṅga (s)– Śikṣā, Kalpa, Vyākaraṇa, Nirukta, Chanda and Jyotiṣa, is an Upādhyāya– if he does it with a purpose of earning his livelihood.
ekadeśantu vedasya vedāṅganyapi vā punaḥ
yo’dhyāpayati vṛttyarthaṃ upādhyāyaḥ sa ucyate.
In the dharmasūtra(s), Manusaṃhitā and Mahābhārata-Purāṇa, the most revered position of Ācārya had been continued, in course of tradition since the Vedic ages. Even before imparting Vedavidyā, at the time of giving Upanayana, the greatness of Ācārya is established saying that the Ācārya assimilates the disciple within his own self at the time of Upanayana, as a mother contains the womb in her body. The Ācārya has been compared to Yama, the god of Death, because Yama imparted Vedavidyā to Naciketā. He is also compared to Varuṇa, because he imparted Vedavidyā to Bhṛgu. Finally the Ācārya’s identity is unique, as it is said that the Ācārya is the true Brahmacārī, because he is always in the process of of teaching Veda(s) to the disciples, and in this way, he also gets indentified with the Brahmacārī–
ācārya brahmacārī brahmacārī prajāpatiḥ.
In fact, the identification of Ācārya with the Brahmacārī indicates his continuous involvement in the process of practicing and cultivating Vedic knowledge.