But when the further epistemological question is asked: 'How is external reality known to exist?' this third group of thinkers, who believe in external reality, give two different answers. Some of them, called Sautrāntikas, hold that external objects are not perceived but known by inference. Others, known as Vaibhāṣikas, hold that the external world is directly perceived. Thus we have the four schools, representing the four important standpoints.
