Sutra 1.2 defines yoga as the stilling of the mind's fluctuations, and a few sutras later Patañjali names what is being stilled. Patañjali claims that every movement of the mind, waking or sleeping, is one of these five. Sleep is one that surprises people, since it appears here as an activity of the mind rather than a blank space in it. Listing these five gives us something particular to watch for instead of a vague instruction to quiet down.