Yoga Sutras 1.1-1.4: What is Yoga?
1.1 Now, after having done prior preparation through life and other
practices, the study and practice of Yoga begins.
1.2 Yoga is the control (nirodah, regulation, channeling, mastery,
integration, coordination, stilling, quieting, setting aside) of the
modifications (gross and subtle thought patterns) of the mind field.
1.3 Then the Seer abides in Itself, resting in its own True Nature,
which is called Self-realization.
1.4 At other times, when one is not in Self-realization, the Seer
appears to take on the form of the modifications of the mind field,
taking on the identity of those thought patterns.