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Some people nowadays say only the Shruti (Vedas) is the sole authority in regard to Dharma, and what is not Shruti, like the Smriti, Dharma Shastras, Puranas, etc. is man-made and can be rejected.

Is this position logical according to the Rishis and ancient Acharyas?

Ancient Acharyas say that it is only logical to accept the validity of Smriti, because the expounders of Shruti also expound the Smriti. Hence, the Smriti is based on Shruti.

Firstly, we accept the Vedas as eternal and divine because Vedic scholars say so. In other words, we have trust in Vedic scholars and the Vedic Sampradayas that produce very learned, trustworthy, and religious Vedic scholars. So when those Vedic scholars say, "The Vedas are divine and eternal," we believe them.

The expounders of the Vedas are the basis for the trustworthiness of the Vedas. This is the basis for the trustworthiness of the Vedas.

Now there might be some sectarian differences, like Nyayas believe the Vedas were divinely composed by Ishvara. Some others say the Vedic swaras are eternal, but the Rishis composed the words of the Vedas.

Either way, what almost all ancient Vedic sampradayas believe is that the Vedas are eternal and the primary authority for spiritual matters.

Having established that the Vedas are the foremost authority because they are eternal, what about Smritis which are authored? Do Smritis have any authority?

This question is answered in the ancient, very important work called the Purva Mimamsa Sutras, which were authored by Jaimini Rishi, who was a sishya of Vedavyasa.

1.3.1 - [Purvapaksha] In as much as Dharma is based upon the
Veda, what is not Veda should be disregarded.

1.3.2 - [Siddhanta] But Smriti is trustworthy, as there would be inference (assumption, of the basis in the Veda) from the fact of
the agent being the same.

1.3.3 - When there is conflict between Shruti and Smriti, the Smriti should be disregarded; because it is only when there is no such
conflict that there is an inference of Vedic text in support of
Smriti.

Sutra 1 is the opponent's viewpoint. The opponent is saying that everything that is not a Vedic text should be disregarded because only the Veda is the source of Dharma.

Sutra 2 is challenging that and saying that the memory of the expounders of the Vedas is also a Pramana. This is the position of Jaimini himself. He wrote this Sutra. There were thousands of Vedic shakhas in existence in ancient times, and only a handful have survived today. The Dharma Shastras are a summary of the topics of particular Vedic Shakhas, and the Smriti is the recollection of the expounders of that Shakha.

In other words, at one point, there may have been a Vedic shakha that enjoined certain things not existing in any extant shakha, but the Vedic text that enjoined that practice was lost, and the only thing that is left is the "memory" of the expounders of the Vedas. This is what is meant by Smriti.

Basically, Sutra 2 is saying just as the Parampara expounds the Vedas, they also expound the recollections that were presumably once based on the Vedas.

So, it is illogical to believe Vedic scholars when they say "This is a Vedic text," and not believe them when they say "This is a Vedic injunction, but I have lost the text."

And it is especially illogical to accuse them of fabricating verses, because then you can just as well accuse them of tampering with the Vedic texts.

And finally, Sutra 3 just says that when there is a conflict between Shruti and Smriti, discard Smriti and go with Shruti, because the inference of a lost Vedic text to corroborate a Smriti verse is only valid when there is no conflict between Shruti and Smriti. In other words, since Smriti presupposes Shruti, if an extant Shruti text refutes a Smriti text, then the Shruti text is more valid since it is direct perception of a Vedic passage, and direct perception is always stronger than inference.

Manu also lists the 4 sources of Dharma:

2.6 - The entire Veda is the root-source of Dharma; also the
Conscientious Recollection of righteous persons versed in the Veda,
the Practice of Good (and learned) Men, and their self-satisfaction.

"The entire Veda" is Shruti.

"Recollection of righteous persons" is Smriti.

"Practice of Good and learned Men" is Achara.

"Their self-satisfaction" is Atmanastushti.

Also, the Vedas themselves say that Smriti is valid.

The Chhandogya Upanishad itself says that the Puranas and Itihasas are the 5th Veda:

7.1.2 - Nârada said: 'I know the Rig-veda, Sir, the Yagur-veda, the Sâma-veda, as the fourth the Âtharvana, as the fifth the
Itihâsa-purâna (itihāsapurāṇaṃ pañcamaṃ vedānāṃ)

Same with the Brihadaranyaka Upanishad, which says that even the Smriti was inspired by Brahman:

2.4.10 - 'As clouds of smoke proceed by themselves out of a lighted fire
kindled with damp fuel, thus, verily, O Maitreyî, has been breathed
forth from this great Being what we have as Rig-veda, Yagur-veda,
Sama-veda, Atharvâṅgirasas, Itihâsa (legends), Purâna (cosmogonies),
Vidyâ (knowledge), the Upanishads, Slokas (verses), Sûtras (prose
rules), Anuvyâkhyânas (glosses), Vyâkhyânas (commentaries) 1. From him
alone all these were breathed forth.

The Taittiriya Samhita of the Krishna Yajur Veda says that the Manusmriti is authoritative:

Whatever Manu has said is beneficial.

And finally, quotes from various Dharma Shastras:

Baudhāyana, Dharmasūtra, 1.1.6.—‘Dharma has been enjoined in each
Veda.’ ‘The second source of knowledge consists of the Smṛtis.’ ‘The
third is what proceeds from the cultured, i. e., those persons who are
free from jealousy and selfishness, fairly well off, free from
avarice, haughtiness, greed, delusion, and anger.’ ‘Those persons are
cultured who have studied the Vedas along with their supplements and
who are versed in the art of making deductions from them; those are
the persons from whom the direct knowledge of Śruti can be derived.’

Gautama, Dharmasūtra, 1.1-2.—‘Veda is the source of Dharma’: ‘the
Smṛti and Śīla of persons learned in the Veda.’

Āpastamba, Dharmasūtra, 1.2-3.—‘The convention of persons knowing
Dharma is authoritative’: ‘and also the Vedas.’

Vaśiṣṭha, Smrti, 1.4-6.—‘In the absence of Śruti and Smṛti, the custom
of the cultured is authoritative’: ‘those persons are cultured whose
mind is free from selfish desires’: ‘that is to be regarded as Dharma
which is not prompted by a selfish motive.’

Yajñavalkya, Smṛti, 1-7.—‘Śruti, Smṛti, the practice of good men,
self-satisfaction determination based upon right volition,—these four
are the source of Dharma.’

Āpastamba, Dharmasūtra, 1.4.7.—‘The Śruti is more authoritative than
custom which derives its authority only from assumption (of
corroboration of Śruti).’

Ibid, 30.9.—‘In cases of conflict, what is stated in the Śruti is more
authoritative.’

Therefore, it stands that all ancient Acharyas accept the authority of Smriti, and that there is a logical foundation for accepting both Smriti and Shruti.

Anyways, this is what Swami Vivekananda, on whose birthday National Youth's Day is celebrated and whose work is used to understand complex and huge data of Shastras on Hinduism even by Supreme Court of India till today.

https://en.wikisource.org/wiki/The_Complete_Works_of_Swami_Vivekananda/Volume_3/Lectures_from_Colombo_to_Almora/Reply_to_the_Address_of_Welcome_at_Madura

There are two sorts of truth we find in our Shâstras, one that is based upon the eternal nature of man — the one that deals with the eternal relation of God, soul, and nature; the other, with local circumstances, environments of the time, social institutions of the period, and so forth. The first class of truths is chiefly embodied in our Vedas, our scriptures; the second in the Smritis, the Puranas. etc. We must remember that for all periods the Vedas are the final goal and authority, and if the Purânas differ in any respect from the Vedas, that part of the Puranas is to be rejected without mercy. We find, then, that in all these Smritis the teachings are different. One Smriti says, this is the custom, and this should be the practice of this age. Another one says, this is the practice of this age, and so forth. This is the Âchâra which should be the custom of the Satya Yuga, and this is the Achara which should be the custom of the Kali Yuga, and so forth. Now this is one of the most glorious doctrines that you have, that eternal truths, being based upon the nature of man, will never change so long as man lives; they are for all times, omnipresent, universal virtues. But the Smritis speak generally of local circumstances, of duties arising from different environments, and they change in the course of time. This you have always to remember that because a little social custom is going to be changed you are not going to lose your religion, not at all. Remember these customs have already been changed. There was a time in this very India when, without eating beef, no Brahmin could remain a Brahmin; you read in the Vedas how, when a Sannyasin, a king, or a great man came into a house, the best bullock was killed; how in time it was found that as we were an agricultural race, killing the best bulls meant annihilation of the race. Therefore the practice was stopped, and a voice was raised against the killing of cows. Sometimes we find existing then what we now consider the most horrible customs. In course of time other laws had to be made. These in turn will have to go, and other Smritis will come. This is one fact we have to learn that the Vedas being eternal will be one and the same throughout all ages, but the Smritis will have an end. As time rolls on, more and more of the Smritis will go, sages will come, and they will change and direct society into better channels, into duties and into paths which accord with the necessity of the age, and without which it is impossible that society can live.

Shrutis/Vedas are Para Vidya https://en.wikipedia.org/wiki/Para_Vidya

Parā Vidyā (Sanskrit: परा विद्या) is a combination of two words – parā, in Hindu philosophy, means - existence, paramount object, the highest point or degree, final beatitude; and vidyā means - knowledge, philosophy, science, learning, scholarship.[1] Para Vidya means –
higher learning or learning related to the Self or the Ultimate Truth i.e. transcendental knowledge.[2] Vedanta affirms that those who gain
the knowledge of the Self attain kaivalya, they become liberated, they
become Brahman

There were two different kinds of knowledge to be acquired – 'the
higher knowledge' or Para Vidya (Sanskrit: परा विद्या )and 'the lower
knowledge' or Apara Vidya. The lower knowledge consists of all textual
knowledge - the four Vedas, the science of pronunciation etc., the
code of rituals, grammar, etymology, metre and astrology. The higher
knowledge is by which the immutable and the imperishable Atman is
realized, which knowledge brings about the direct realization of the
Supreme Reality, the source of All. The knowledge of the Atman is very
subtle Smritis are Apara Vidya

Basically, we have Dharma, Artha, Kama and Moksha

Dharma = Apara Vidya = Smritis/Puranas = Different Religions = Rivers

Moksha = Para Vidya = Shrutis/Vedas = One God = Ocean

Donot live in rivers/wells, come to ocean, you can swim back later to rivers/religion, first come to ocean/God.

Donot go by the books/theory, go by the practical/heart/Soul that lives in you.