The main or basic section of the YBh is structured around seventeen "bhūmis" (explained in fourteen books), which are "foundations" or "groundings" of meditation, referring to "a field of knowledge that the Yogācāra acolyte ought to master in order to be successful in his or her yoga practice." Some of these are doctrinal topics such as the five "vijñānas" (book 1), the "ālayavijñāna", afflictive cognition "(kliṣṭaṃ manaḥ)," the 51 mental factors (book 2)"," and the defilements ("saṃkleśa," book 3). Other books discuss meditation practice proper (books 4, 9, 10, and 12).