Chapter 1, sutra 6 "The fivefold vrttis of the mind are: valid proofs, perversive cognition, imaginary cognition, sleep and memory." Swami Veda Bharati
Explanation: This sutra lays out the five major types of thought waves, which will be described individually in the upcoming sutras. The five types of thought waves, vrittis, in the mind, chitta, that the yogi seeks to master are: 1) Valid cognition or valid proofs (pramaana), 2) Perversive or false cognition (viparyaya), 3) Imaginary or misconceived cognition (vikalpa), 4) deep dreamless sleep ( nidraa), and 5) Memory ( smriti). MInd is an internal organ with three functions: cognition, will, and retention. Mental waves that are directly experienced are called pratyaya, and those that are subtle latent impressions are called samskara.