What is the relationship between Rig Veda, Sama Veda and Yajur Veda?

The relationship between Rig Veda, Yajur Veda, Sama Veda and Atharva #Veda is very intimate and integral.

I will attempt to cover as many aspects of this relationship that I can remember to the best of my knowledge. Please note that here only the samhitA portions are meant, because the brAhmaNa, AraNyaka and upaniShad texts have their own names.

1. Content: Rig Veda has the most original, sublime and ancient hymns, and it is the foundational text containing the seeds that inspired all of India’s philosophies and religions through the ages. Sama Veda borrows about 80% of Rig Veda hymns intact. Yajur Veda has about 40% of Rig Veda (mainly because it has a lot of prose text). Atharva Veda has about 20% of Rig Veda, and it also has some ancient, original and very sublime hymns that greatly influenced later philosophy to almost same extent as Rig Veda.
2. Style: Rig Veda, Atharva Veda and Sama Veda are fully metrical. In other words, they are 100% comprised of hymns composed in specific poetic meters (Sanskrit “chandas” छन्दः). Krishna Yajur Veda is a mixture of prose and metrical hymns. Shukla Yajur Veda is 100% metrical. Traditional terms for the style of Vedic text are mantra (मन्त्रः) and brAhmaNam (ब्राह्मणम्). According to commentator Sayanacharya, anything that is not a mantra is considered a brAhmaNam. A mantra is defined by a rishi (by whom it was “seen”), a devatA (to whom it is dedicated), and a chandas (in which it is constructed). So Rig, Sama and Atharva are fully mantra. Krishna Yajus is mixture of mantra and brAhmaNam (hence the name “krishna”). Shukla Yajus is fully mantra (hence the name “shukla”).
3. Liturgical purpose: Rig Veda has all the hymns that provide the prayers and means of expression to address the deities. Sama sets these hymns into musical elaboration. Yajus includes details on when, where, how and with what instruments these hymns are to be used. Atharva does not seem to have a key role in the performance of yajnas.

References in the literature itself:

1. Rig Veda 10.90.9 (Purusha Suktam):

तस्माद्यज्ञात्सर्वहुतः ऋचः सामानि जज्ञिरे । छन्दांसि जज्ञिरे तस्माद्यजुस्तस्मादजायत ॥

“From that all-encompassing universal yajna, the Rks (Rig Veda mantras) and the sAmans (Sama Veda musical elaborations) were born. The meters were born, and the yajus was born.”

So philosophically, all the Vedas were born together from that primeval act of creation. It means that the concept and idea of the Vedas was ever-existing and eternal. Note here that the Rks represent the metrical style of hymns of both Rig Veda and Atharva Veda.

2. Taittiriya Upanishad 1.5.2:

भूरिति वा ऋचः । भुव इति सामानि । सुवरिति यजूंषि । मह इति ब्रह्म ॥

In the first chapter (shIkShAvalli), during the discourse on the 3 vyAhRtis (mystic utterances, aids in meditation), they are successively identified with various sets. One such set is the set of Vedas. So bhUh = Rig Veda, bhuvah = Sama and suvah = Yajus. The fourth silent vyAhRti is mahah = Brahman.

3. Taittiriya Upanishad 2.3:

तस्माद्वा एतस्मात्प्राणमयात् । अन्योऽन्तर आत्मा मनोमयः । तेनैष पूर्णः । … तस्य यजुरेव शिरः । ऋग्दक्षिणः पक्षः । सामोत्तरः पक्षः । … अथर्वाङ्गिरसः पुच्छं प्रतिष्ठा ॥

In the second chapter, the so-called Anandavalli, there is the teaching of the pancakosha vidyA (the five sheaths in the form of persons supposed to cover the Atman). The third sheath is the mental sheath (manomaya kosha). This sheath is imagined as the repository of knowledge, and his ‘head’ is the Yajus, his ‘right arm’ is the Rig, his ‘left arm’ is the Sama, and his base or back is the Atharva. Obviously, because this Upanishad belongs to the Yajur Veda, the Yajus is given the primary position.

4. Chandogya Upanishad 1.1.2:

एषां भूतानां पृथिवी रसः पृथिव्या आपो रसोऽपामोषधयो रस ओषधीनां पुरुषो रसः पुरुषस्य वाग्रसो वाच ऋग्रस ऋचः साम रसः साम्न उद्गीथो रसः ।

“Of these great elements, the earth is the essence; of the earth, water is the essence; of water, plants are the essence; of plants, man is the essence; of man, speech is the essence; of speech, Rks are the essence; of Rks, sAma is the essence; of sAma, udgItha is the essence.”

So the word “essence” is interpreted slightly differently for each link in the sequence above, but the context should be self-evident. So in the end, Sama Veda is seen as a further enhancement or refinement of Rig Veda, due to being put into musical form. “udgItha” is a specific portion of a sAmagAna, roughly corresponding to the crescendo.

5. Chandogya Upanishad 1.6:

इयमेव ऋगग्निः साम तदेतदेतस्यां ऋच्यध्यूढं साम तस्मादृच्यध्य़ूढं साम गीयते इयमेव साग्निरमस्तत्साम

“The earth is the Rk, Agni is the sAma. The sAma is founded upon the Rk, therefore the sAma is sung based upon the Rk. The earth is ‘sA’ and Agni is ‘ama’. The conjoining of the two results in ‘sAma’.”

Such meditation aids are common in the Upanishads. The aim of these aids is to show similarities in different aspects and thus help deduce the unity.

Natyashastra

This is the treatise on dance and drama by Bharatamuni. In the first chapter, the origin of the nATyaveda is explained by means of a mythical story. Apparently the gods in heaven were bored and they asked Prajapati Brahma to create some entertainment that was audio-visual.

The nATyaveda was supposed to be the fifth Veda that was accessible to groups that were forbidden to read the original four Vedas. So the nATyaveda was conceptualized as a summary of the four Vedas. This is evident in the ingredients that Brahma used to create nATyaveda:

जग्राह पाठ्यमृग्वेदात् सामभ्यो गीतमेव च ।

यजुर्वेदादभिनयान् रसानाथर्वणादपि ॥ 1.17

“He took the text or lyrics from Rig Veda, the music from the Sama Veda, the actions from Yajur Veda, and the navarasas (emotions) from Atharva Veda.”