How do different Astika schools prove the existence of God?

Question

There are two kinds of schools of Indian philosophy, Astika and Nastika. Astikas accept the authority of the Vedas, whereas Nastikas reject the authority of the Vedas. The Astika schools are part of Hinduism, while the Nastika schools fall under the broader category of Dharmic faiths. Now there are six Astika schools: Samkhya, Yoga, Nyaya, Vaisheshika, Purva Mimamsa, and Vedanta. (They're all dead other than the Vedanta school, which encompasses most Hindus today as I discuss here.)

Because they accept the authority of the Vedas, these schools all believe in Yagnas, the law of Karma, the existence of the soul, the afterlife, reincarnation, and Moksha. But one thing they disagree on is on the existence of God and how to prove it. Two Astika schools are atheist or agnostic on the existence of God: Samkhya and Purva Mimamsa. I discuss their arguments on the subject here. The other four Astika schools, namely Yoga, Nyaya, Vaisheshika, and Vedanta, accept the existence of God. My question is, how do each of these four schools prove the existence of God?

Answer 1

Let me address each of the four Astika schools which unequivocally accept the existence of God:

1. Yoga: Here is what Vyasa says in this excerpt from the Yoga Bhashya:

   This seed of omniscience is the cognition of the [smallness] or [largeness] of the perception of supersensorious objects past, present, and future, individually as well as collectively. And that person is omniscient in whom this seed has grown to its utmost extent. There is a gradual progress of the seed of omniscience because it has various degrees like Dimension. That person in whom wisdom attains its limit, is omniscient; and this is a particular spirit. The above inference, ending in only a general conclusion, is not capable of denoting any particular being; consequently, the knowledge of particular names is to be looked for in the scripture.

   This reminds of me of Aquinas' Fourth Way. In any case, as the end of the quote makes clear, the Yoga school thought that the only the existence of God can be proved through Anumana or inference; the qualities of God are known through Sabda Pramana.

2. Nyaya: Here is what Gautama says in Adhyaya 4 Pada 1 of the Nyaya Sutras:

   19. īśvaraḥ kāraṇaṁ puruṣakarmāphalyadarśanāt
       God is the cause; because we find fruitlessness in the actions of Men.
       
   20. na puruṣakarmābhāve phalāniṣpatteḥ
       It is not so; because as a matter of fact, no fruit appears without man's action.
       
   21. tatkāritatvādahetuḥ
       Inasmuch as it is influenced by Him, there is no force in the reason (put forward).

   And here is what Vatsyayana says in the Nyaya Sutra Bhashya:

   As a matter of fact, we find that Man, desiring a certain thing, does not always obtain the fruit of his desire; hence it is inferred that Man's acquisition of the fruits of his actions is dependent upon some other person; and that person upon whom it is dependent is God; hence it follows that God is the Cause[.]... "If the appearance of fruits were dependent on God, then such fruits could be accomplished even without the desire of man." ... As a matter of fact, God helps the effort of Man; i.e., when Man is trying to obtain a particular fruit, it is God that accomplishes that fruit for him; when God does not accomplish it, Man's action becomes fruitless; hence since things are thus influenced by God, what has been urged to the effect that - "as a matter of fact no fruit appears without Man's action" - is no reason at all.

   It's also worth noting that the Nyaya and Vaisheshika schools eventually merged into a single school known as Navyanyaya. This process started with the 10th century philosopher Udayana, who composed a Nyaya-Vaisheshika work called the Nyaya Kusumanjali which gives 9 arguments, mostly based on Anumana or inference, for the existence of God. You can read it here.

3. Vaisheshika: Here is what Kanada says in Adhyaya 2 Pada 1 of the Vaisheshika Sutras:

   18. saṃjñākarma tvasmadviśiṣṭānāṃ liṅgam

   But name and effect are the mark (of the existence) of beings distinguished from ourselves.

   19. pratyakṣapravṛttatvāt saṃjñākarmaṇaḥ

   Because name and effect follow from perception.

   Here is what Shankara Mishra says in this from the Upaskara:

   [H]e only is competent to give the names "Heaven," "Apurva", etc., with whom "Heaven," "Apurva", etc. are objects of sense-perception[.]... Similarly, the application of the names "pot," "cloth," etc., is only under tho direction of Ishvara. The word which has been directed by Ishvara in a particular place, the same is appropriate there; e.g., "all those herbs which have been touched by the edge of the mongoose's tooth, counteract the venom of the snake." Such direction is the mark, i.e., the means of inference, of beings distinguished from ourselves. And the name, "Maitra" etc., which the father gives to the son, that also is surely directed by Ishvara by such rules as "The father should give a name (to the son) on the twelfth day." Thus it is proved that naming is a mark of the existence of Ishvara.

   In like manner action, i.e., effect, also is a mark of the existence of Ishvara ; for, thus, Earth, etc., must have a creator, because they are effects like a pot, etc.

   The part at the end is known in Western philosophy as the cosmological argument. This argument is spelled out in a bit more detail in this excerpt from Sridhara's Nyaya Kandali:

   The four Great Elementary Substances are preceded by someone having knowledge of them, because they are effects, - anything that is an effect is preceded by one having a cognition of it, as for instance, the jar (which is always preceded by the potter), - and the four Great Elementary Substances are effects, hence they must be preceded by one having knowledge of them.... "The premise of this inference is not duly cognized by any means of right motion, - f.i. the fact of the Earth being an effects cannot be regarded as duly established." ... This is not right; as the Earth etc. made up of parts; and everything made up of parts is an effect, as for instance the jar; the Earth etc. have parts, - hence they must be effects.

4. Vedanta Here is what Vyasa says in the Brahma Sutras:

   1. athāto brahmajijñāsā
      Hence (is to be undertaken) thereafter a deliberation on Brahma.
      

   2. janmādyasya yataḥ
      That (is Brahman) from which (are derived) the birth etc., of this (universe).

   3. śāstrayonitvāt

   (Brahman is not known from any other source), since the scriptures are the valid means of Its knowledge.

   4. tat tu samanvayāt
      
 But that Brahman (is known from the Upanishads), (It) being the object of their fullest import.

   The Vedanta school approaches proving the existence of God in a very different manner than the other Astika schools. In contrast to the other Astika schools which use Anumana to argue for the existence of God and then try to show that God is the author of the Vedas, the Vedanta school uses the Vedas to prove the existence of God. There are many objections that might be made to this approach, but the Vedanta school refutes them all. First of all how do we know that the Vedas are authoritative? The Pramanya (authoritativeness) and Apaurusheyatva (authorlessness) of the Vedas is proved in Adhyaya 1 Pada 1 of the Purva Mimamsa Sutras. All right, the Vedas are authoritative, but how can they be authoritative concerning Brahman, if Brahman's existence can already be proven using Anumana? That's where Sutra 3 comes in. The Vedanta school shows that all attempts to prove the existence of Brahman through Anumana are invalid. For instance, see my answer here for Ramanujacharya's refutation of the cosmological argument for the existence of God. All right, the Vedas are authoritative and no other Pramana can prove the existence of God, but still how can the Vedas be authoritative concerning Brahman, if as the Purva Mimamsa school says action is the only purport of the Vedas? That's where Sutras 4 comes in. The Vedanta school shows that action is not the only purport of the Vedas, and that the Vedas are authoritative concerning Brahman. See the commentaries on the Brahma Sutras for details.