The Yoga system of Indian Philosophy stands in close relation to the Samkhya system, adopting its metaphysics though it adds a twenty-sixth principle (the supreme lord, ishvara) to Samkhya's list of twenty-five. While Samkhya is primarily intellectualistic and emphasizes metaphysical knowledge as the means to liberation, Yoga is voluntaristic and emphasizes the need for self-control as the means to liberation.
The Yoga Sutras of Patanjali is the primary book of Yoga philosophy. a short work of 196 aphorisms divided into four chapters (pada).
The first chapter is the Samadhi Pada, which is concerned with the general nature of yoga and its technique. It defines yoga in its famous second aphorism as the “cessation of the mind’s fluctuations” (yogas chitta-vrtti-nirodhah). This chapter describes the fluctuations, modifications, and modulations of thought which disturb pure consciousness and then begins to describe means (practice/abhyasa and detachment/vairagya) by which they may be stilled. A method to achieve the goal of yoga is formulated by which the spirit (purusa) is isolated from nature (prakrti) by means of mind control.
The second chapter of the Yoga Sutras, the Sadhana Pada, begins by delineating the afflictions which disturb the mind and answers why one should practice yoga. It ourtlines the five external yogic practices of the eight-fold yogic path (ashtanga-yoga): abstentions (yama) or nonviolence (ahimsa), truthfulness (satya), nonstealing (asteya), continence (brahmacarya), and nonpossession (aparigraha).
The third chapter, Vibhuti Pada, sets down the last three limbs of the eight-fold yoga; concentration (dharana), meditation (dhyana), and Samadhi, and then speaks of the divine effects of yogic practices.
Finally, chapter four Kaivalya, gives a general exposition of how the study and practice of yoga eventually leads to liberation.