The foundational text of the yoga philosophy is the Yoga Sutras by Patanjali. It’s part of the Mauryan sutra corpus, that is: the earliest part of the text was composed somewhere between 321B and 185BC. The Yoga Sutras are a very short text of concentrated verses. Because it’s so concentrated, the Sanskrit is extremely hard to translate. This means that most translations are in fact translations plus commentaries. There are a LOT of commentaries on the Yoga Sutras, because every Indian spiritual teacher of note has written one. Every teacher aspiring to greatness has also written a translation/commentary. In addition to that, the most famous commentaries have also been commented on.
Yoga is establishing the mind (chitta) in stillness. (Ravi Ravindra, The Wisdom of Patanjali’s Yoga Sutras: A New Translation and Guide, p. 5)
The most famous sentence in the whole sutras is the second verse, which defines yoga. Personally I think that the direction of the commentary can usually be extracted from the translators idea on how that verse should be read. From the definition of yoga, everything else follows.
Philosophy in the Yoga Sutras
While the yoga sutras, like all yoga philosophy, mainly address yoga as a spiritual path, they also point to a philosophy. The philosophy of the Yoga Sutras is mainly based on the Samkhya philosophy of ancient India, but you’ll also find the influence of Jainism, Buddhism and the Upanishads.
Summary of the Yoga Sutras
Some religious historians feel that the Yoga Sutras show unmistakable signs of Buddhist influence. Yama and Niyama in particular are literally identical to lists of Buddhist lay vows and commitments.
Yoga Sutra Translations and Commentaries
In general any ‘Yoga Sutra’ translation you’ll find is also a commentary. In fact, anybody who is anybody, and anybody who aspires to be somebody, in Hinduism and Yoga has written a commentary on the Yoga Sutras. The Yoga Sutras by Patanjali themselves is a very short text. It’s only a few pages when printed out on an ordinary printer. The tradition of commenting ON the yoga sutras has been going on for about 2000 years (or more, depending on who you ask) and is extensive. In general you will want a commentary from within your own spiritual tradition – but I’ve also listed a few that stand out in terms of their linguistic thoroughness or originality in their approach. How about a commentary by a Western Tibetan Buddhist Geshe? See The Essential Yoga Sutra: Ancient Wisdom for Your Yoga by Geshe Michael Roach.
Yoga Sutras by Patanjali, Science of Yoga, by I.K. Taimni
This is a commentary on the Yoga Sutras of Patanjali in the light of modern thought. The translation by I.K. Taimni is a very scholarly commentary on THE yoga classic: the Yoga Sutras by Patanjali. Taimni not only explains each sutra, but also puts them in the context of Indian philosophy in general. As a scientist he also uses graphs to explain his interpretation and relates his insights to the scientific insights of his day (20th century).