Dating back at least to the Sa?dhinirmocana Sutra is a classification of the corpus of Buddhism into three categories, based on ways of understanding the nature of reality, known as the "Three Turnings of the Dharma Wheel". According to this view, there were three such "turnings":
1. In the first turning, the Buddha taught the Four Noble Truths at Vara?asi for those in the sravaka vehicle. It is described as marvelous and wonderful, but requiring interpretation and occasioning controversy. The doctrines of the first turning are exemplified in the Dharmacakra Pravartana Sutra. This turning represents the earliest phase of the Buddhist teachings and the earliest period in the history of Buddhism.
2. In the second turning, the Buddha taught the Mahayana teachings to the bodhisattvas, teaching that all phenomena have no-essence, no arising, no passing away, are originally quiescent, and essentially in cessation. This turning is also described as marvelous and wonderful, but requiring interpretation and occasioning controversy. Doctrine of the second turning is established in the Prajñaparamita teachings, first put into writing around 100 BCE. In Indian philosophical schools, it is exemplified by the Madhyamaka school of Nagarjuna.
3. In the third turning, the Buddha taught similar teachings to the second turning, but for everyone in the three vehicles, including all the sravakas, pratyekabuddhas, and bodhisattvas. These were meant to be completely explicit teachings in their entire detail, for which interpretations would not be necessary, and controversy would not occur. These teachings were established by the Sa?dhinirmocana Sutra as early as the 1st or 2nd century CE. In the Indian philosophical schools, the third turning is exemplified by the Yogacara school of Asa?ga and Vasubandhu.