What is the means of attaining Moksha according to the different Astika schools?
Let me address each of the six Astika schools:
Samkhya: The Samkhya school believed that meditation on the 25 Tattvas, i.e. Purusha or soul, Prakriti or matter/energy, and the 23 evolutes of Prakriti, is what leads to knowledge of the difference between Purusha and Prakriti, which is what leads to Moksha. Here is what Ishwara Krishna says in verses 64-66 of the Samkhya Karika:
evaṃ tattvābhyāsān nāsmi na me nāham ity apariśeṣam |
aviparyayād viśuddhaṃ kevalam utpadyate jñānam ||
tena nivṛttaprasavām arthavaśāt saptarūpavinivṛttām |
prakṛtiṃ paśyati puruṣaḥ prekṣakavad avasthitaḥ svasthaḥ ||
dṛṣṭā mayetyupekṣaka eko dṛṣṭāham ityuparatānyā |
sati saṃyoge api tayoḥ prayojanaṃ nāsti sargasya ||
By practising the principles thus, there arises the knowledge, viz., ‘I am not, naught is mine, there is no Ego’, which is complete, absolute and pure, because there remains no doubt. By this knowledge, the Spirit, seated composed like a spectator, perceives the Nature which has ceased to be productive and, consequently, which has now reverted from seven forms. One (the Spirit) is indifferent like a spectator in play; one (the Nature) desists, (saying) that I have been seen. (Now), in spite of their contact, there is no motive for creation.
Yoga: The Yoga school believed that practicing Ashtanga Yoga is what leads to knowledge of the difference between Purusha and Prakriti, which is what leads to Moksha. Here is what Patanjali says in Adhyaya 2 Sutras 25-29 of the Yoga Sutras:
tad-abhābāt-saṁyoga-abhāvo hānaṁ taddr̥śeḥ kaivalyam ||
viveka-khyātir-aviplavā hānopāyaḥ ||
tasya saptadhā prānta-bhūmiḥ prajña ||
yoga-aṅga-anuṣṭhānād-aśuddhi-kṣaye jñāna-dīptir-āviveka-khyāteḥ ||
yama niyama-āsana prāṇāyāma pratyāhāra dhāraṇā dhyāna samādhayo-'ṣṭāvaṅgāni ||
The bringing of this association to an end, by bringing the darkness of unwisdom to an end, is the great liberation; this is the Seer's attainment of his own pure being. A discerning which is carried on without wavering is the means of liberation. His illuminations is sevenfold, rising in successive stages. From steadfastly following after the means of Yoga, until impurity is worn away, there comes the illumination of thought up to full discernment. The eight means of Yoga are: the Commandments, the Rules, right Poise, right Control of the life-force, Withdrawal, Attention, Meditation, Contemplation.
Nyaya: The Nyaya school believed that knowledge of the 16 Padarthas or categories of logical reasoning and argument is what leads to Moksha. Here is what Gautama says in the first Sutra of the Nyaya Sutras:
pramāṇa-prameya-saṃśaya-prayojana-dṛṣṭānta-siddhānt-avayava-tarka-nirṇaya-vāda-jalpa-vitaṇḍā-hetvābhāsa-cchala-jāti-nigrahasthānānī tattva-jñānān niśreyasa-adhigamaḥ
It is the knowledge of the real essence (or true character) of the following sixteen categories that leads to the attainment of the Highest Good -
- The means of Right Cognition
- The objects of Right Cognition
- Factors of Inference
- Demonstrated Truth
- Fallacious Reason
- Futile Rejoinders
Vaisheshika: The Vaisheshika school believed that knowledge of the 7 Padarthas or qualities of existence is what leads to Moksha. Here is what Kanada says in the fourth Sutra of the Vaisheshika Sutras.
dharma-viśeṣa-prasūtād dravya-guṇa-karma-sāmānya-viśeṣa-samavāyānāṃ padārthānāṃ sādharmaya-vaidharmyābhyāṃ tattva-jñānān niḥśreyasam
The Supreme Good (results) from the knowledge, produced by a particular dharma, of the essence of the Predicables, Substance, Attribute, Action, Genus, Species, and Combination by means of their resemblances and differences.
Purva Mimamsa: The Purva Mimamsa school wasn't too focused on Moksha, being more concerned with the fruits obtained from Yagnas. But those Mimamsakas that did believe in Moksha thought that knowledge of the Jivatma of individual soul is what leads to Nishkama Karma, i.e. doing your Vedic Dharma without desiring the fruit, and that Nishkama is what leads to Moksha. Here is what Kumarila Bhatta says in this excerpt from the Shloka Vartika:
The fact (as to the manner of Deliverance) is that for those that have come to know of the real character of Self,—all their past actions having been exhausted by fruition, and there being no subsequent residue (of actions),—the body is never again produced (and this is what is meant by Deliverance). It is only for the purpose of enjoying the results of our past actions that our body is produced; consequently, when there are no actions (left to bring about their results), there is no cause left for such productions (of the body). One desiring Deliverance, therefore, would not engage in (i.e., perform) such actions as are either prohibited or are enjoined with a view to the attainment of certain (material) results. But he would continue to perform those that are enjoined as necessary (and to be performed daily), and those that are enjoined as to be performed on certain specific occasions (such as eclipses and the like),—in order to avoid the sin (accruing from | the non-performance of such actions). The effects (of the necessary sacrifices f.i.) are known to result only when they are desired by the agent ; and as such they could not accrue to one who does not desire them. And as this (aversion to results) exists in one who knows one's real self, it is in this that such knowledge comes to be of indirect use (to the attainment of Deliverance).
Some Mimamsakas went further and added that the performance of Vedic Dharma should not only be desireless, but it should be done as devotional service to Brahman. Here is what Apadeva says in this excerpt from his Mimamsa Nyaya Prakasha:
And this duty, when it is performed with a view to that with a view to which it is enjoined, produces that (promist fruit). But performed with the intention to offer it to the Exalted Govinda, it produces supreme beatitude. And there is no lack of authority for performing it with the intention of offering it to Him. Because there is the traditional statement: "Whatever tho doest, whatever thou eatest, whatever thou offerest as oblation or givest in gifts, whatever penance thou doest, Son of Kuntï, that do as an offering to Me." And because this (statement) is valid authority, like the smriti-prescription of the Eighth-lunar-day-rite etc. This is set forth in full elsewhere.
But other Mimamsakas didn't even believe in Brahman.
Vedanta: The Vedanta school believes that meditation on Brahman using the 32 Brahmavidyas is what leads to knowledge of Brahman, which is what leads to Moksha. Here is what Vyasa says in Adhyaya 4 Pada 1 Sutras 12-14 of the Brahma Sutras
ā prayāṇāt tatrāpi hi dṛṣṭam ||
tadadhigama uttarapūrvāghayoraśleṣavināśau tadvyapadeśāt itarasyāpyevamasaṃśleṣaḥ pāte tu
(Meditation is to be repeated) up till the moment of death, for it is noticed in the scriptures that it is done so even then. On the realization of That, there occur the non-attachment and destruction of the subsequent and previous sins respectively, because it is declared so. In the very same way there is no attachment of the other (ie., of virtue) as well. Liberation must follow as soon as the body falls.
But getting Moksha through meditation upon Brahman is extremely difficult, especially in the Kali Yuga, so Krishna describes an easier alternative path to Moksha in chapter 18 of the Bhagavad Gita:
sarva-dharmān parityajya mām ekaṁ śaraṇaṁ vraja | ahaṁ tvāṁ sarva-pāpebhyo mokṣayiṣyāmi mā śucaḥ ||
Abandon all varieties of religion and just surrender unto Me. I shall deliver you from all sinful reactions. Do not fear.
This refers to Sharanagati or complete surrender to the lotus feet of Vishnu, as Vedanta Desikan explains in this excerpt from his Rahasyatraya Sara.
In any case, it's striking that all six Astika schools agree that knowledge/meditation of some kind leads to Moksha.
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