The basic problem of Shankara’s philosophy is how such pure consciousness appears, in ordinary experience, to be individualized (“my consciousness”) and to be of an object (“consciousness of blue”). As he stated it, subject and object are as opposed to each other as light and darkness, yet the properties of one are superimposed on the other. If something is a fact of experience and yet ought not to be so—i.e., is rationally unintelligible—then this must be false. According to Shankara’s theory of error, the false appearance is a positive, presented entity that is characterized neither as existent (because it is sublated when the illusion is corrected) nor as nonexistent (because it is presented, given as much as the real is). The false, therefore, is indescribable either as being or as nonbeing; it is not a fiction, such as a round square. Shankara thus introduced a new category of the “false” apart from the usual categories of the existent and the nonexistent. The world and finite individuals are false in this sense: they are rationally unintelligible, their reality is not logically deducible from brahman, and their experience is cancelled with the knowledge of brahman. The world and finite selves are not creations of brahman; they are not real emanations or transformations of it. Brahman is not capable of such transformation or emanation. They are appearances that are superimposed on brahman because of human ignorance. This superimposition was sometimes called adhyasa by Shankara and was often identified with avidya. Later writers referred to avidya as the cause of the error. Thus, ignorance came to be regarded as a beginningless, positive something that conceals the nature of reality and projects the false appearances on it. Shankara, however, did distinguish between three senses of being: the merely illusory (pratibhasika), the empirical (vyavaharika; which has unperceived existence and pragmatic efficacy), and transcendental being of one, indeterminate brahman.

In his epistemology, Shankara’s followers in general accepted the point of view of the Mimamsa of Kumarila’s school. Like Kumarila, they accepted six ways of knowing: perception, inference, verbal testimony, comparison, nonperception, and postulation. In general, cognitions are regarded as modifications of the inner sense in which the pure spirit is reflected or as the pure spirit limited by respective mental modifications. The truth of cognitions is regarded as intrinsic to them, and a knowable fact is accepted as true so long as it is not rejected as false. In perception a sort of identity is achieved between the form of the object and the form of the inner sense; in fact, the inner sense is said to assume the form of the object. In their theory of inference, the Nyaya five-membered syllogism is rejected in favor of a three-membered one. Furthermore, the sort of inference admitted by the Nyaya, in which the major term is universally present, is rejected because nothing save brahman has this property according to the system.

Shankara regarded moral life as a necessary preliminary to metaphysical knowledge and thus laid down strict ethical conditions to be fulfilled by one who wants to study Vedanta. For him, however, the highest goal of life is to know the essential identity of his own self with brahman, and, though moral life may indirectly help in purifying the mind and intellect, over an extended period of time knowledge comes from following the long and arduous process whose three major stages are study of the scriptures under appropriate conditions, reflection aimed at removing all possible intellectual doubts about the nondualistic thesis, and meditation on the identity of atman and brahman. Moksha is not, according to Shankara, a perfection to be achieved; it is rather the essential reality of one’s own self to be realized through destruction of the ignorance that conceals it. God is how brahman appears to an ignorant mind that regards the world as real and looks for its creator and ruler. Religious life is sustained by dualistic concepts: the dualism between mortal and God, between virtue and vice, and between this life and the next. In the state of moksha, these dualisms are transcended. An important part of Shankara’s faith was that moksha was possible in bodily existence. Because what brings this supreme state is the destruction of ignorance, nothing need happen to the body; it is merely seen for what it really is—an illusory limitation on the spirit.

Shankara’s chief direct pupils were Sureshvara, the author of Varttika (“Gloss”) on his bhashya and of Naishkarmya-siddhi (“Establishment of the State of Nonaction”), and Padmapada, author of Panchapadika, a commentary on the first five padas, or sections, of the bhashya. These early pupils raised and settled issues that were not systematically discussed by Shankara himself—issues that later divided his followers into two large groups: those who followed the Vivarana (a work written on Padmapada’s Panchapadika by one Prakashatman in the 12th century) and those who followed Vachaspati’s commentary (known as Bhamati) on Shankara’s bhashya. Among the chief issues that divided Shankara’s followers was the question about the locus and object of ignorance. The Bhamati school regarded the individual self as the locus of ignorance and sought to avoid the consequent circularity (arising from the fact that the individual self is itself a product of ignorance) by postulating a beginningless series of such selves and their ignorances. The Vivarana school regarded both the locus and the object of ignorance to be brahman and sought to avoid the contradiction (arising from the fact that brahman is said to be of the nature of knowledge) by distinguishing between pure consciousness and valid knowledge (pramajnana). The latter, a mental modification, destroys ignorance, and the former, far from being opposed to ignorance, manifests ignorance itself, as evidenced by the judgment “I am ignorant.” The two schools also differed in their explanations of the finite individual. The Bhamati school regarded the individual as a limitation of brahman just as the space within the four walls of a room is a limitation of the big space. The Vivarana school preferred to regard the finite individual as a reflection of brahman in the inner sense. As the moon is one but its reflections are many, so also brahman is one but its reflections are many. Later followers of Shankara, such as Shriharsha in his Khandanakhandakhadya and his commentator Chitsukha, used a destructive, negative dialectic in the manner of Nagarjuna to criticize humanity’s basic concepts about the world.