In Tibetan Buddhism, Ngöndro (, ) refers to the preliminary, preparatory or foundational practices or disciplines (Sanskrit: sādhanā) common to all four schools of Tibetan Buddhism and also to Bon. They precede deity yoga. The preliminary practices establish the foundation for the more advanced and esoteric Vajrayana sādhanā which are held to engender realization and the embodiment of Dzogchen, Heruka and Mahamudra. Nevertheless, Vajrayana masters are careful to point out that "foundational" does not mean "lesser," that the practice of Ngöndro is a complete and sufficient practice of the spiritual path, and that it can take the practitioner all the way to full enlightenment. In addition to what is generally denoted by the term ngöndro, preparatory practices may also be prescribed for senior and advanced sadhana, e.g.: "differentiating saṃsāra and nirvāṇa" () is the preparatory practice for trekchö or "cutting through to primordial purity." Outer and inner preliminaries In general the preliminary practices are divided into two sections or kinds: the first are the common or ordinary kind of preliminary practices, and the second are the special or extraordinary kind of preliminaries. Outer preliminaries The common or ordinary preliminaries consists of a series of deep reflections or contemplations on the following four topics: the freedoms and advantages of precious human rebirth the truth of impermanence and change the workings of karma the suffering of living beings within samsara The above four contemplations are sometimes referred to as "the four reminders" or "the four mind-changers" or "the four thoughts which turn the mind towards Dharma." Additional reflections may be included in the specific instructions on the outer preliminaries within different lineages, but the above four topics are the main reflections. N.B.: the Four Ordinary Foundations should not be conflated with the Satipatthana. Inner preliminaries The special or extraordinary kind of preliminaries consist of: taking of refuge in the Three Jewels in conjunction with the performance of 100,000 prostrations (purifying pride) cultivation of bodhicitta (purifying jealousy). In some formulations this is included under 1. 100,000 recitations of Vajrasattva's hundred-syllable mantra (purifying hatred/aversion) 100,000 mandala offerings (purifying attachment) 100,000 guru yoga practices (purifying delusion) Traditionally ngöndro practice is done for the enlightenment of the spiritual aspirant and for the benefit of all sentient beings. That is, the merit of doing the practices is dedicated to all sentient beings. These practices can take 1,500 hours of work to accomplish once. Some practitioners do them