It is defined again in the Sūtra. Yoga is the movement of the mind in one direction. It presumes:
1. There is something in each of us called mind.
2. This mind has many movements or activities.
3. It is possible to channelise these movements through certain actions.
4. When we accept movement we accept time and space – moving something from A to B. There are realities.
5. In accepting vṛtti we also accept the idea of an object.
6. We can fix the mind so it confines itself to an object.”
– TKV Desikachar on Yoga Sūtra Chapter One verse 2