Originating around a set of scriptures and treatises composed by such early masters as Vasubandhu and the legendary Maitreyanatha, this school held a prominent position in the Indian scholastic tradition for several centuries. It was also transmitted to Tibet, where its teachings became an integral part of much of Tibetan Buddhism up to modern times, and to East Asia, where it was studied with intensity for several centuries.
Yogācāra eventually died out as a distinct school in East Asia, along with other scholastic traditions. One reason for this was the evaporation of the state patronage that was essential to the survival of scholastic traditions like Yogācāra. Another was the overwhelming competition from more readily understandable, practice-oriented traditions like Chan (Zen) and Pure Land. Yet although it would eventually die out as a distinct school, the teachings of Yogācāra brought a deep and lasting influence on the basic technical vocabulary of all forms of Buddhism that developed in Tibet and East Asia. This is because it was the Yogacarins who took it upon themselves to provide a detailed analysis of the functions of consciousness, as well as the effects that Buddhist practices such as morality, concentration and wisdom have on the consciousness, and how those effects bring one to the Buddhist goal of enlightenment.
The Yogācāra texts cover a vast array of topics, but one of their central foci is explaining how it is possible for human beings to perceive the world, and then to agree on what they perceive. This kind of problem is especially important in a religious system like Buddhism, where the doctrine of emptiness effectively denies the reality of any set positions of awareness.
The Yogacaras defined three basic modes by which we perceive our world: one, through attached and erroneous discrimination, wherein things are incorrectly apprehended based on preconceptions; two, through the correct understanding of the dependently originated nature of things; and three, by apprehending things as they are in themselves, uninfluenced by any conceptualization at all. These are referred to in Yogācāra as the three natures of perception. Also, regarding perception, the Yogacaras emphasized that our everyday understanding of the existence of external objects is problematic, since in order to perceive any object (and thus, for all practical purposes for the object to "exist"), there must be a sensory organ as well as a correlative type of consciousness to allow the process of cognition to occur.
Perhaps the best known teaching of the Yogācāra system is that of the eight layers of consciousness. This theory of the consciousnesses attempted to explain all the phenomena of cyclic existence, including how rebirth occurs and precisely how karma functions on an individual basis. For example, if I carry out a good or evil act, why and how is it that the effects of that act do not appear immediately? If they do not appear immediately, where is this karma waiting for its opportunity to play out?
The answer given by the Yogacaras was the store consciousness (also known as the base, or eighth consciousness; Skt., alaya-vijnana) which simultaneously acts as a storage place for karma and as a fertile matrix that brings karma to a state of fruition. The likeness of this process to the cultivation of plants led to the creation of the metaphor of seeds (Skt, bijas) to explain the way karma is stored in the eighth consciousness. The type, quantity, quality and strength of the seeds determine where and how a sentient being will be reborn: one's species, sex, social status, proclivities, bodily appearance and so forth.
On the other hand, the karmic energies created in the current lifetime through repeated patterns of behavior are called habit energies (Skt., vasanas). All the activities that mold our minds and bodies, for better or worse--eating, drinking, talking, studying, practicing the piano or whatever--can be understood to create habit energies. And of course, my habit energies can penetrate the consciousnesses of others, and vice versa--what we call "influence" in everyday language. Habit energies can become seeds, and seeds can produce new habit energies.
There are two important aspects of the Yogācāra schemata that are of special interest to modern-day practitioners. One is that virtually all schools of Mahayana Buddhism came to rely on these Yogācāra explanations as they created their own doctrinal systems--even the Zen schools. For example, the important Yogācāra explanation of the pervasiveness of one's delusions through "mind-only" had an obvious influence on Zen.
The other interesting thing about the Yogācāra teachings is the extent to which they can be correlated with modern understandings of life as seen in fields such as psychology, genetics and evolutionary biology. For example, Yogācāra views regarding seeds appear to have many correlations with our understanding of the function of DNA--especially observing the way species are able to produce genetic mutations to adapt and survive to new environments. They can also help to explain things such as hereditary diseases, as well as the function of group karma in recovering from diseases.
That Yogācāra is not yet that well known among the community of Western practitioners is probably attributable to the fact that most of the initial transmission of Buddhism to the West has been directly concerned with more practice-oriented forms of Buddhism, such as Zen, Vipassana, and Pure Land. Also, it is a complicated system, and there are still not really any good, accessible, introductory books on the topic in Western languages. But as the Western understanding of Buddhism matures, it will be very useful for us if we can round out our theoretical understanding of Buddhism by studying a bit about Yogācāra.