Cute Young Brunette Girl Practicing Yoga Poses

These two are regarded in India as twins, the two aspects of a single discipline. Sāṅkhya provides a basic theoretical exposition of human nature, enumerating and defining its elements, analyzing their manner of co-operation in a state of bondage ("bandha"), and describing their state of disentanglement or separation in release ("mokṣa"), while Yoga treats specifically of the dynamics of the process for the disentanglement, and outlines practical techniques for the gaining of release, or "isolation-integration" ("kaivalya").
Patanjali is widely regarded as the founder of the formal Yoga philosophy. Patanjali's yoga is known as Raja yoga, which is a system for control of the mind. Patanjali defines the word "yoga" in his second sutra, which is the definitional sutra for his entire work:
योग: चित्त-वृत्ति निरोध: