Yoga Sutras 1.17-1.18: Types of concentration
Building upon practice (abhyasa) and non-attachment (vairagya), the
meditator systematically moves inward, through four levels or stages
of concentration on an object, and then progresses to the stage of
objectless concentration. Virtually all types, styles, methods, or
objects of meditation are included in one of these four stages,
levels, or categories.
1.17 The deep absorption on an object is of four kinds, 1) gross
(vitarka), 2) subtle (vichara), 3) bliss accompanied (ananda), and 4)
with I-ness (asmita), and is called samprajnata samadhi.
1.18 The other kind of samadhi is asamprajnata samadhi, and has no
object in which attention is absorbed, wherein only latent
impressions remain; attainment of this state is preceded by the
constant practice of allowing all of the gross and subtle
fluctuations of mind to recede back into the field from which they