Yoga Sutra - Sādhana Pada 2.28
योगाङ्गानुष्ठानादशुद्धिक्षये ज्ञानदीप्तिराविवेकख्यातेः ॥२८॥
yoga-aṅga-anuṣṭhānāt aśuddhi-kṣaye jñāna-dīptiḥ āviveka-khyāteḥ ||28||
From following the limbs of yoga, on the destruction of impurity there is a light of knowledge, leading to discriminative discernment.
Upon the destruction of impurities as a result of the practice of yoga, the lamp of knowledge arises. This culminates in discriminative discernment.
Patañjali here introduces the long-awaited aṇgas, limbs of yoga. It has by now been well established, says Vyāsa, that discriminative discernment, viveka, when achieved, is the cause of removing the conjunction between puruṣa and prakṛti, in other words, of removing ignorance such that liberation manifests. But what is the cause of achieving discriminative discernment? A means is required to achieve this. Milk may exist in the udders of the cow, says Vācaspati Miśra, but one needs a means or process to extract it. The means presented in this sūtra of attaining discriminative discernment is the practice of the eight limbs of yoga, yogā ṅgānuṣṭhāna, which will occupy the rest of the chapter.
By the practice of yoga, Patañjali states, impurity, aśuddhi, is destroyed, which, Vyāsa, reminds us, consists of the five kleśas, obstacles to yoga (ignorance, ego, attachment, aversion, and clinging to life). The notion of yoga destroying impurities goes back as far as the Āpastamba-dharma-sūtra of the fifth and fourth centuries B.C.E., which lists fifteen doṣas, faults, that are eliminated by its practice. When impurity is removed, the light of full knowledge, jñāna-dīpti, noted in this sūtra can shine forth, like the sun after the cold season, says Śaṅkara. Another way of putting this is that as the impurities of tamas and rajas dwindle, the luminosity and clarity inherent in sattva can manifest unimpeded. An impurity is something that intrudes on or contaminates another entity, in this case, rajas and tamas covering sattva (of course, sattva itself is ultimately a covering of puruṣa). The more the eightfold path is practiced, the more these impurities dwindle, and the more they dwindle, the more this light can correspondingly increase. This increase culminates in the desired discriminative discernment, a feature of pure sattva. Just as the axe slices wood from a tree, so the practice of these eight limbs slices the impurities away from the citta, says Vyāsa.
There is the widespread view that the continuity of the text comes to something of an abrupt end after II.27, with this sūtra typically deemed as initiating a new self-contained unit on the eight limbs. It is true that Patañjali does not make reference to the eight limbs prior to this point. Nor is there any explanation of the relationship among tapas, svādhyāya, and Īśvara-pranidhāna as the three ingredients of kriyā-yoga, and their occurrence as three of the five niyamas, the second limb, discussed below. And our modern notions of discursive continuity might have put the eight-limbed section in a separate pāda of its own, beginning with this sūtra.
But, again, one must be wary of submitting the cryptic sūtra style to modern notions of structural coherence. Just as the kriyā-yoga section introduced a new set of terms and conceptual analyses indispensable to explaining the mechanics (kleśas) underpinning the vṛttis such that the attainment of the goal of yoga might be better understood, so does this ensuing section dedicate itself to a necessarily more specific elaboration of the abhyāsa, practice, touched upon in I.12. As with the kriyā-yoga section, this increase of detail requires new terms and categories, but now pertaining to practice, articulated accordingly with less philosophical tone and content.
It is likely that Patañjali drew upon an existing tradition of eight-limbed yoga when composing his text (or modified the older tradition of six limbs), as well as a distinct tradition featuring kriyā-yoga. In other words, as a systematizer of existing traditions, Patañjali might well have merged two distinct but overlapping systems. This possibility is enhanced by the fact that the relationship between the three ingredients of kriyā-yoga and the identical three ingredients reappearing in the second limb of yoga, the niyamas, but now alongside two other ingredients, is not addressed by Patañjali.