“In this Sūtra, Patañjali lists the five types of mental activities:
Pramāṇa Vṛtti, Viparyaya Vṛtti, Vikalpa Vṛtti, Nidrā Vṛtti, and Smṛti Vṛtti.
Vṛtti and Pariṇāma are synonymous, meaning “change of form”.
These five Vṛtti represent changes in the characteristics and functions of the mind.”
– T Krishnamacharya on Yoga Sūtra Chapter One verse 6
T Krishnamacharya Yoga Sūtra Study Quotes Collected and Collated