The term “yoga” etymologically can be derived from two different Sanskrit roots. Each root assigns completely different meanings to the term. One of the meanings is predominantly used in the system of Vedanta, the other in the historical school of yoga, called Yoga Darshana. But which meaning is the one that the school of yoga assigns to its own name?
The following is an excerpt from an explanation of sutra I.1 contained in my 2006 text Ashtanga Yoga Practice and Philosophy:
I.1 Now then authoritative instruction in yoga.
The word atha, translated here as ‘now then’, signals the start of an authoritative treatise. The Brahma Sutra, for example, starts with the stanza ‘athatho brahmajninasya’ which means ‘Then therefore inquiry into consciousness’. Patanjali’s treatise on grammar, the Mahabhasya, starts with ‘atha sabdanusasanam’, which means ‘Now then inquiry into sound’. What is implied with the use of atha is that the author is not relaying someone else’s understanding but has mastered the subject as set out in the text. In other words, the author is in a position to make such a statement. This is reflected in the fact that all later generations of yogis have accepted Patanjali as an authority.
The term yoga is then defined. According to Panini, the term yoga can be derived from either of two roots, yujir yoge and yujir samadhau. If we derive it out of yujir yoge it means ‘union’ or ‘bringing together’. The Bhagavad Gita accepts this meaning. The Gita teaches that there is one deep reality underlying all phenomena, which is the Supreme Being. Yoga here means to unite oneself with or merge into this underlying or deep reality. All scriptures and meditation systems that propose one truth contained in all appearances, and therefore take yoga to mean union, are called non-dualistic (meaning not-two) or monistic (from mono – one).
The second root out of which we can derive the term yoga is yujir samadhau, which gives it the meaning of ‘contemplation’ or ‘absorption’. It is this meaning that the Yoga Sutra follows. The basic concept of the Yoga Sutras is that there are two separate realities, nature (prakrti) and consciousness (purusha). Yoga here means the contemplation that enables us to discriminate between the two. Scriptures and meditation systems that distinguish between two essential categories, and therefore take yoga to mean contemplation, are called dualistic. This will be covered in detail later.
We know that the Yoga Sutra employs the second meaning of the word yoga (i.e. the meaning of absorption/contemplation) because of a clear statement made by the Rishi Vyasa. In his commentary on the Yoga Sutra – Yoga Bhasya – he explained every sutra with such clarity that no misunderstanding was possible. It is mainly through the work of Vyasa that we know the meaning of the sutras. Many of them are so concise and cryptic that they cannot be understood without his explanations. It has been mentioned that Vyasa’s commentary is so important that it and Patanjali’s sutras together are regarded as virtually the one book.
For today’s yoga student it is vital to realise that the historical school of yoga does not consist only of Patanjali’s sutras but also of Vyasa’s commentary and various other sub-commentaries as well. The authoritative sub-commentaries are those of Vachaspati Mishra (ninth century CE), Shankara (eighth century CE) and Vijnanabhikshu (fifteenth century CE). The authoritative twentieth-century commentary, by Hariharananda Aranya, is outstanding in its depth. All yoga masters after Vyasa accepted his commentary and wrote sub-commentaries on it.
The Rishi Vyasa states in his commentary on sutra I.1 that yoga means absorption/contemplation (yogah samadhih). He also explains that contemplation is a potential of the mind (chitta). This potential is dormant in most and needs to be trained and developed. Yoga, then, is the science of training the mind, and it is for those who are in need of this training. There are those who do not need the training but can see the one true reality in all appearances. They can bypass yoga and go instead to the Vedanta, which is the science of consciousness, explained by the Rishi Vyasa in the Brahma Sutra.
Those who do not realise their true nature are advised to take up the study of yoga. Yoga is the process that prepares a clouded mind for self-knowledge. In other words, the study of yoga starts by us admitting our ignorance and knowing that we first have to change ourselves before we can see the truth.
Neither of the two paths described in the Brahma Sutra and the Yoga Sutra is right or wrong. Rather, they apply to different students. For the advanced soul, the path of the Brahma Sutra (Vedanta) is recommended. For a more confused student, the clarifying of the mind through yoga is recommended first.
 Panini is the leading authority on classical Sanskrit grammar. In his Ashtadyayi he listed two thousand word roots and, out of these, with the help of rules called guna and vriddhi, we can form verbs, nouns, various endings and the like. According to western scholars he lived around 500 BCE; according to Indian tradition, however, he lived more than six thousand years ago. Patanjali wrote a commentary on Panini’s Ashtadyayi called the Great Commentary (Mahabhasya). In India it is generally understood that Patanjali the yoga master and Patanjali the grammarian are one and the same person, though some western scholars doubt this. In this text we follow respectfully the traditional Indian view. It is in the context of its tradition that yoga must be understood.
With the exception of King Bhoja (tenth century), who wrote his explanation (called Raja Martanda) directly on Patanjali’s sutras.