Visistadvaita Theory is a non-dualistic school of Vedanta philosophy. The other major sub-schools of Vedanta are Advaita and Dvaita. It is a school of Hindu philosophy. Visistadvaita theory believes in non-dualism of the qualified whole in which the Brahman alone exists but is characterised by multiplicity. It is like a kind of qualified monism. It is a school of Vedanta philosophy which believes in all diversity subsuming to an underlying unity. The only reality according to them is Brahman as qualified by the sentient and insentient modes. The relationship of God to the Soul and the Universe is like the relationship of the Soul of Man to the body of Man. Individual souls are only parts of Brahman. God, Soul and Universe together form an inseparable unity which is one and has no second. This is the non-duality part. Matter and Souls inhere in that Ultimate Reality as attributes to a substance. This is the qualification part of the non-duality.

Philosophers of the Visistadvaita Theory
The theory of Visistadvaita theory is said to have been in existence for a long time, so long in fact that the earliest and most original works are no longer available. The names of the earliest philosophers who propounded the Visistadvaita Theory are only known through Ramanuja`s Veda Artha Sangraha. In fact one of the most prominent philosophers of the Visistadvaita theory is Ramanuja. He continued along the line of his predecessors while expounding the knowledge expressed in the Upanishads, Brahma Sutras and Bhagavad Gita. Among the other philosophers who advocated the Visistadvaita system, the most prominent ones are Guhadeva, Kapardi, Dramida, Bodhayana, Tanka and Bharuci. Besides these philosophers, Ramanuja`s teacher Yamunacharya is credited with laying the foundation for what culminates as the Sri Bhashya. The disciples of Ramanuja, Vedanta Desika and Pillai Lokacharya, due to certain minor disagreements on the Visistadvaita theory, gave rise to the Vadakalai and Thenkalai schools of thought.

Principles of Visistadvaita Theory
There are three basic principles which underlie the theory of Visistadvaita theory, namely Tattva, Hita and Purushartha. Tattva refers to the knowledge of the three real entities, namely Jiva, (the sentient being), Jagat (the insentient one) and Ishwara (Vishnu- Narayana or Parabrahman). Purushartha is the goal to be attained, i.e. moksha or liberation from bondage. Hita is the means of realization, i.e., through Bhakti (devotion) and Prapatti (self-surrender).

Tattva
The belief of Visistadvaita theory centers around the concept of the relationship between the Ishwara (Parabrahman), the sentient beings, i.e., chit and Brahman and the insentient Universe (achit-brahman). The Ishwara is said to be the Universal Soul consisting of the Universe and sentient beings. The three entities are briefly discussed below.

Ishwara
Ishwara is said to be the Supreme Cosmic Spirit denoted by Vishnu Narayana. He is said to maintain complete control over the Universe and all the sentient beings, which together also form the pan-organistic body of Ishwara. The triad of Ishwara along with the universe and the sentient beings is Brahman, which signifies the completeness of existence. He is said to be the Parabrahman who is endowed with numerous qualities known as Kalyana Gunas. Ishwara is considered to have a 2-fold characteristic: he is the indweller of all beings and all beings also reside in Ishwara.

Chit
Chit is the world of sentient beings, or of entities possessing consciousness. The sentient beings are called Jivas and they are possessors of individual consciousness as denoted by "I". This is called Dharmi jnana or substantive consciousness. The sentient beings also possess varying levels of Dharma-bhuta-jnana or attributive consciousness. These jivas have three different types of existence, the Nityas or the eternally free jivas, the Muktas or the free jivas that were once in Samsara and the Baddhas or the jivas which are still in samsara.

Achit
Achit is the world of insentient entities as denoted by matter or more specifically the non-conscious Universe.

Brahman
There is a subtle difference between Ishwara and Brahman. Ishwara is the substantive part of Brahman, while jivas and jagat are its modes (also secondary attributes), and kalyana gunas (auspicious attributes) are the primary attributes. Brahman is the description of Ishwara when comprehended in fullness i.e. a simultaneous vision of Ishwara with all his modes and attributes.

Theory of Existence
Visishtadvaita adheres to a system of complete reality. The three ontological entities i.e. Ishwara, Chit and Achit are fundamentally real. It upholds the doctrine of Satkaryavada. Satkaryavada is pre-existence of the effect in the cause. It maintains that karya (effect) is sat or real. It is present in the karana (cause) in a potential form, even before its manifestation.

Purushartha
The purpose of human existence is said to be Purushartha. According to the Vedas, there are four goals namely Artha (wealth), Kama (pleasure), Dharma (righteousness) and Moksha (permanent freedom from worldly bondage). According to this philosophy, the first three goals are not an end by themselves but need to be pursued with the ideal of attaining Moksha.

Moksha
Moksha is the main goal and end to be achieved. It is a state where the jiva becomes one with the Brahman in terms of all knowership and possessing qualities free from all worldly evils and defects. The Moksha does not involve destruction of the self ("I") consciousness of the jiva.

Hita
Bhakti Yoga is the sole means of liberation in Visistadvaita. Through Bhakti (devotion), a Jiva ascends to the realm of the Lord, where it continues to delight in His service. Karma Yoga and Jnana Yoga are natural outcomes of Bhakti, total surrender, as the devotee acquires the knowledge that the Lord is the inner self. A devotee realizes his own state as dependent on, and supported by, and being led by the Lord, who is the Master. One is to lead a life as an instrument of the Lord, offering all his thought, word, and deed to the feet of the Lord. One is to see the Lord in everything and everything in Him. This is the unity in diversity achieved through devotion.

Thenkalai and Vadakalai Schools of Thought
Vedanta Desika, one of the foremost learned scholars of medieval India, wrote more than a hundred works in Sanskrit language and the Tamil language. The Vadakalai sect of Sri Vaishnavism associates themselves with Vedanta Desika. Pillai Lokacharya is associated with the Tenkalai sect of Sri Vaishnavism. He was a contemporary of Vedanta Desika. Both were the followers of Ramanuja. Pillai Lokacharya confirmed the basics of the Sri Vaishnava system in his 18 works popularly known as Ashtadasa Rahasyangal ("the eighteen secrets") also called the Rahasya granthas ("doctrines that explain the inner meanings").

Thus discussed above are the basic tenets and belief system of the Visistadvaita system. It is a Pantheistic belief system since Narayana is said to be Absolute and the Soul and the Universe are only parts of this Absolute. The importance of the Visistadvaita philosophy can be understood from the fact that it provided the philosophical basis for the establishment of Sri Vaishnavism. It also gave a strong backing to the devotion of the Alwar saints and their beautiful compositions in praise of Lord Vishnu.