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 man's 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 favour 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.

Moksa 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 man and God, between virtue and vice, and between this life and the next. In the state of moksa, these dualisms are transcended. An important part of Shankara's faith was that moksa 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 bhasya and of Naiskarmya-siddhi ("Establishment of the State of Non-Action"), and Padmapada, author of Pancapadika, a commentary on the first five padas, or sections, of the bhasya. 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 Pancapadika by one Prakashatman in the 12th century) and those who followed Vacaspati's commentary (known as Bhamati) on Shankara's bhasya. 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 Shriharsa in his Khandanakhandakhadya and his commentator Citsukha, used a destructive, negative dialectic in the manner of Nagarjuna to criticize man's basic concepts about the world.
 
 

The philosophies of transcendence and immanence  (bhedabheda) assert both identity and difference between the world and finite individuals, on the one hand, and Brahman, on the other. The world and finite individuals are real and yet both different and not different from the Brahman.

 Among pre-Shankara commentators on the Vedanta-sutras, Bhartrprapanca defended the thesis of bhedabheda, and Bhaskara (c. 9th century) closely followed him. Bhartrprapanca's commentary is not extant; the only known source of knowledge is Shankara's reference to him in his commentary on the Brhadaranyaka Upanisad, in which Bhartrprapañca is said to have held that though Brahman as cause is different from Brahman as effect, the two are identical inasmuch as the effect dissolves into the cause, as the waves return into the sea. Bhaskara viewed Brahman as both the material and the efficient cause of the world. The doctrine of maya was totally rejected. Brahman undergoes the modifications by his own power. As waves are both different from and identical with the sea, so are the world and the finite individuals in relation to Brahman. The finite selves are parts of Brahman, as sparks of fire are parts of fire. But the finite soul exists, since beginningless time, under the influence of ignorance. It is atomic in extension and yet animates the whole body. Corresponding to the material world and the finite selves, Bhaskara ascribed to God two powers of self-modification. Bhaskara, in his theory of knowledge, distinguished between self-consciousness that is ever-present and objective knowledge that passively arises out of appropriate causal conditions but is not an activity. Mind, thus, is a sense organ. Bhaskara subscribed to the general Vedanta thesis that knowledge is intrinsically true, though falsity is extrinsic to it. In his ethical views, Bhaskara regarded religious duties as binding at all stages of life. He upheld a theory known as jnana-karmasamuccaya-vada: performance of duties together with knowledge of Brahman leads to liberation. In religious life, Bhaskara was an advocate of bhakti, but bhakti is not a mere feeling of love or affection for God, but rather is dhyana, or meditation, directed toward the transcendent Brahman who is not exhausted in his manifestations. Bhaskara denied the possibility of liberation in bodily existence.

 The bhedabheda point of view had various other adherents: Vijnanabhiksu, Nimbarka, Vallabha, and Caitanya.

Ramanuja (11th century) sought to synthesize a long tradition of theistic religion with the absolutistic monism of the Upanisads, a task in which he had been preceded by no less an authority than the Bhagavadgita. In his general philosophical position, he followed the vrttikara Bodhayana, the Vakyakara (to whom he referred but whose identity is not established except that he advocated a theory of real modification of Brahman), Nathamuni (c. 1000), and his own teachers' teacher Yamunacarya (c. 1050).
 
 

The main religious inspirations are from the theistic tradition of the Alvar poet-saints and their commentators known as the Acaryas, who sought to combine knowledge with action (karma) as the right means to liberation. There is also, besides the Vedic tradition, the religious tradition of Agamas, particularly of the Pancaratra literature. It is within this old tradition that Ramanuja's philosophical and religious thought developed.

 Ramanuja rejected Shankara's conception of Brahman as an indeterminate, qualityless, and differenceless reality on the ground that such a reality cannot be perceived, known, thought of, or even spoken about, in which case it is nothing short of a fiction. In substantiating this contention, Ramanuja undertook, in his Shri-bhasya on the Vedanta-sutras, a detailed examination of the different ways of knowing. Perception, either nonconceptualized or conceptualized, always apprehends its object as being something, the only difference between the two modes of perception being that the former takes place when one perceives an individual of a certain class for the first time and thus does not subsume it under the same class as some other individuals. Nor can inference provide one with knowledge of an indeterminate reality, because in inference one always knows something as coming under a general rule. The same holds true of verbal testimony. This kind of knowledge arises from understanding sentences. For Ramanuja there is nothing like a pure consciousness without subject and without object. All consciousness is of something and belongs to someone. He also held that it is not true that consciousness cannot be the object of another consciousness. In fact, one's own past consciousness becomes the object of present consciousness. Consciousness is self-shining only when it reveals an object to its own owner--i.e., the self.

 Rejecting Shankara's conception of reality, Ramanuja defended the thesis that Brahman is a being with infinitely perfect excellent virtues, a being whose perfection cannot be exceeded. The world and finite individuals are real, and together they constitute the body of Brahman. The category of body and soul is central to his way of thinking. Body is that which can be controlled and moved for the purpose of the spirit. The material world and the conscious spirits, though substantive realities, are yet inseparable from Brahman and thus qualify him in the same sense in which body qualifies the soul. Brahman is spiritual-material-qualified. 
Ramanuja and his followers undertook criticisms of Shankara's illusionism, particularly of his doctrine of avidya (ignorance) and the falsity of the world. For Ramanuja, such a beginningless, positive avidya could not have any locus or any object, and if it does conceal the self-shining Brahman, then there would be no way of escaping from its clutches.

 A most striking feature of Ramanuja's epistemology is his uncompromising realism. Whatever is known is real, and only the real can be known. This led him to advocate the thesis that even the object of error is real--error is really incomplete knowledge--and correction of error is really completion of incomplete knowledge.

 The state of moksa is not a state in which the individuality is negated. In fact, the sense of "I" persists even after liberation, for the self is truly the object of the notion of "I." What is destroyed is egoism, the false sense of independence. The means thereto is bhakti, leading to God's grace. But by bhakti Ramanuja means dhyana, or intense meditation with love. Obligation to perform one's scriptural duties is never transcended. Liberation is a state of blessedness in the company of God. A path emphasized by Ramanuja for all persons is complete self-surrender (prapatti) to God's will and making oneself worthy of his grace. In his social outlook, Ramanuja believed that bhakti does not recognize barriers of caste and classes.

 The doctrinal differences among the followers of Ramanuja is not so great as among Shankara's. Writers such as Sudarshana Suri and Venkatanatha continued to elaborate and defend the theses of the master, and much of their writing is polemical. Some differences are to be found regarding the nature of emancipation, the nature of devotion, and other ritual matters. The followers are divided into two schools: the Uttara-kalarya, led by Venkatanatha, and the Daksina-kalarya, led by Lokacarya. One of the points at issue is whether or not emancipation is destructible; another, whether there is a difference between liberation attained by mere self-knowledge and that attained by knowledge of God. There also were differences in interpreting the exact nature of self-surrender to God and the degree of passivity or activity required of the worshipper.
 
 

Madhva (born 1199?) belonged to the tradition of Vaisnava religious faith and showed a great polemical spirit in refuting Shankara's philosophy and in converting people to his own fold. An uncompromising dualist, he traced back dualistic thought even to some of the Upanisads. His main works are his commentaries on the Upanisads, the Gita, and the Vedanta-sutras. He also wrote a commentary on the Mahabharata and several logical and polemical treatises.

 He glorified difference. Five types of differences are central to Madhva's system: difference between soul and God, between soul and soul, between soul and matter, between God and matter, and that between matter and matter. Brahman is the fullness of qualities, and by his own intrinsic nature, Brahman produces the world. The individual, otherwise free, is dependent only upon God. The Advaita concepts of falsity and indescribability of the world were severely criticized and rejected. In his epistemology, Madhva admitted three ways of knowing: perception, inference, and verbal testimony. In Madhva's system the existence of God cannot be proved; it can be learned only from the scriptures.

 Bondage and release both are real and devotion is the only way to release, but ultimately it is God's grace that saves. Scriptural duties, when performed without any ulterior motive, purify the mind and help one to receive God's grace.

 Among the other theistic schools of Vedanta, brief mention may be made of the schools of Nimbarka (c. 12th century), Vallabha (15th century), and Caitanya (16th century).
 
 

Nimbarka's philosophy is known as Bhedabheda because he emphasized both identity and difference of the world and finite souls with Brahman. His religious sect is known as the Sanaka-sampradaya of Vaisnavism. Nimbarka's commentary of the Vedanta-sutras is known as Vedanta-parijata-saurabha and is commented on by Shrinivasa in his Vedanta-kaustubha. Of the three realities admitted--God, souls, and matter--God is the independent reality, self-conscious, controller of the other two, free from all defects, abode of all good qualities, and both the material and efficient cause of the world. The souls are dependent, self-conscious, capable of enjoyment, controlled, atomic in size, many in number, and eternal but seemingly subject to birth and death because of ignorance and karma. Matter is of three kinds: nonnatural matter, which constitutes divine body; natural matter constituted by the three gunas; and time. Both souls and matter are pervaded by God. Their relation is one of difference-with-ondifference. 
Liberation is because of a knowledge that makes God's grace possible. There is no need for Vedic duties after knowledge is attained, nor is performance of such duties necessary for acquiring knowledge.
 
 

Vallabha's commentary on the Vedanta-sutras is known as Anubhasya ("The Brief Commentary"), which is commented upon by Purusottama in his Bhasya-prakasha ("Lights on the Commentary"). His philosophy is called pure nondualism--"pure" meaning "undefiled by maya." His religious sect is known as the Rudra-sampradaya of Vaisnavism and also Pustimarga, or the path of grace. Brahman, or Shri Krishna, is viewed as the only independent reality; in his essence he is existence, consciousness, and bliss, and souls and matter are his real manifestations. Maya is but his power of self-manifestation. Vallabha admitted neither parinama (of Samkhya) nor vivarta (of Shankara). According to him, the modifications are such that they leave Brahman unaffected. From his aspect of "existence" spring life, senses, and body. From "consciousness" spring the finite, atomic souls. From "bliss" spring the presiding deities, or antaryamins, for whom Vallabha finds place on his ontology. This threefold nature of God pervades all beings. World is real; but samsara, the cycle of birth and death, is unreal, and time is regarded as God's power of action. Like all other Vedantins, Vallabha rejected the Vaishesika relation of samavaya and replaced it by tadatmya, or identity. The means to liberation is bhakti, which is defined as firm affection for God and also loving service (seva). Bhakti does not lead to knowledge, but knowledge is regarded as a part of bhakti. The notion of "grace" plays an important role in Vallabha's religious thought. He is also opposed to renunciation.
 
 

Caitanya (1485-1533) was one of the most influential and remarkable of the medieval saints of India. His life is characterized by almost unique emotional fervour, hovering on the pathological, which was directed toward Shri Krishna (the incarnation of Vishnu). He has not written anything, but the discourses recorded by contemporaries give an idea of his philosophical thought that was later developed by his followers, particularly by Rupa Gosvamin and Jiva Gosvamin. Rupa is the author of two great works: Bhakti-rasamrta-sindhu ("The Ocean of the Nectar of the Essence of Bhakti") and Ujjvalanilamani ("The Shining Blue Jewel"). Jiva's main work is the great and voluminous Satsamdarbha. These are the main sources of the philosophy of Bengal Vaisnavism. Caitanya rejected the conception of an intermediate Brahman. Brahman, according to him, has three powers: the transcendent power that is threefold (the power of bliss, the power of being, and the power of consciousness) and the two immanent powers, namely, the powers of creating souls and the material world. Jiva Gosvamin regarded bliss to be the very substance of Brahman who, with the totality of all his powers, is called God. Jiva distinguished between God's essential power, his peripheral power that creates the souls, and the external power (called maya) that creates cosmic forms. The relation between God and his powers is neither identity nor difference, nor identity-with-difference. 
This relation, unthinkable and suprarational, is central to Caitanya's philosophy. For Jiva, the relation between any whole and its parts is unthinkable. Bhakti is the means to emancipation. Bhakti is conceived as a reciprocal relation between man and God, a manifestation of God's power in man. The works of Jiva and Rupa delineated a detailed and fairly exhaustive classification of the types and gradations of bhakti.