The very first lesson in Patanjali's Yoga Sutra-s is atha yoga anushasanam.

Atha means now.  In sutra 1:1, Patanjali says "now we begin the study of yoga". Some people may interpret this literally.  We have sat down with a book or for a lecture so right now we are beginning this study of yoga. This is true.  However, there is more weight to Atha than that simple now.