Samkhya is the oldest and the most orthodox philosophical system of Hinduism and is said to have been propagated by Sage Kapila. Samkhya states that the Universe consists of two eternal realities :
- Purusha (souls) are numerous in numbers but devoid of qualities and are the silent spectators of Prakriti.
- Prakriti (matter or nature) is composed of three gunas (dispositions) - sattvas, rajas, and tamas (steadiness, activity, and dullness).
The relationship between Purusha and Prakriti is intertwined and
so when the equilibrium of the gunas is disturbed, the world order
needs to evolve. This is a dualistic philosophy in which the
difference is between the self and matter.
Yoga is considered to have arisen from the Samkhya philosophy and is essentially described as a universal method of union with The Supreme. The basis of this philosophy are the four primary systems as mentioned in the Bhagvad Gita: Karma-Yoga; Buddhi-Yoga; Dhyana-Yoga; and Bhakti-Yoga.
Sage Patanjali wrote "Yoga Sutra" on Raja Yoga (meditational Yoga). The difference between Yoga and Samkhya philosophies is that Yoga incorporates the concept of Ishvara who is treated as a personal God and also the ideal for meditation. Ishvara is treated as not being entangled with Prakriti (Nature). Yoga also utilizes the Vedic terminologies and concepts like Brahman. Moksha or Nirvana is said to be the realization of the goal of Life in Yoga.
The Nyaya school of philosophy is said to have been propagated by Aksapada Gautama and is based on texts called the Nyaya Sutras. This philosophy is based on logic.
According to the Nyaya school, there are only four sources of knowledge (pramanas): perception, inference, comparison, and testimony. Knowledge obtained through each of these can be valid or invalid. The practitioners of Nyaya philosophy are called Naiyanikas and they have given logical proofs for the existence of God/Ishvara.
The Vaisheshika system of philosophy was founded by the Sage Kanada and it deals witjh atomic pluralism. According to this school of philosophy, all the objects in the physical universe can be reduced to a certain number of atoms. God is regarded as the fundamental force who causes consciousness in these atoms.
The Vaishesika system merged with Nyaya due to the closely related metaphysical theories. However, Vaishesika differs from Nyaya in one aspect : Nyaya accepts four sources of knowledge whereas Vaisheshika accepts only two - perception and inference.
The main objective of the Purva ("earlier") Mimansa school was to establish the authority of the Vedas and this school of philosophy was propagated by Sage Jaimini. This philosophy formulated the rules of Vedic interpretation. The practitioners of Mimansa are called Mimamsakas and they believe that there should be unquestionable faith in the Vedas, mantras and yajnas that sustain the activity of our Universe.
According to Mimansa, salvation can be attained only by strictly adhering to the Vedic prescriptions. Later on, the thoughts of "Mukti", and doctrines of God were also added to this school.
Uttar Mimansa is also called Vedanta and it concentrates on the philosophical teachings of Upanishads. Vedantic thought was based on Vedic cosmology, hymns and philosophy. This school of philosophy stresses on self discipline, spiritual connectivity and meditation. This philosophy was propagated by Sage Vyasa. Uttar Mimansa also says that consciousness of the Self (Jivatma) is continuous and indistinguishable from the consciousness of the Supreme Spirit (Brahman - Paramatma).
The Uttar Mimansa school of philosophy gave rise to the three main schools of Vedanta :
- Advaita Vedanta : Advaita(not two) refers to a monistic (or non-dualistic) system, which emphasises oneness. It was propagated by AdiShankaracharya who based his theories of advaita on the Upanishads and teachings of his own guru : Govinda Bhagavadpada. He exposed the relative nature of the world and established the non-dual reality of Brahman in which Atman (the individual soul) and Brahman (the ultimate reality) are same. Adi Sankara denounced caste and meaningless rituals.
- Vishistadvaita Vedanta : Ramanujacharya was the propagator of the concept of Sriman Narayana as the supreme Brahman. He taught that ultimate reality had three aspects : Ishvara (Vishnu), Cit (soul) and Acit (matter). Vishnu is the only independent reality, while souls and matter are dependent on God for their existence.
- Dvaita Vedanta : Madhvacharya identified God with Vishnu. But he said that there was a difference between the individual soul and the Ultimate Soul. Thus his system is called Dvaita.
The concept of Bhakti takes its name from the Hindu term that signifies a blissful, selfless and overwhelming love of God. Bhakti is seen as a form of Yoga, or union and it seeks to dissolve the ego in God. It is believed by the folowers of Bhakti school of thought that it is God who brings about all changes, is the source of all works, and acts through the devotee as love and light. 'Sins' and evil-doings of the devotee are said to fall away of their own accord due to the love of God towards his devotees. The most popular means of expressing love for God in the Hindu tradition is through puja.
The word "Tantra" means treatise and is applied to a variety of mystical, occult, medical and scientific works. The Tantra Shastra is a development of the Vedic Karmakanda, promulgated to meet the needs of that age. Tantra has given birth to or influenced ritual, yoga, and sadhana of all kinds.