Hinduism consists of a voluminous body of thought and philosophy arranged within a number of different schools and tendencies, developed over the course of centuries as scholars revisited or provided commentaries on existing literature. The particular configurations of thought and literature involved in Hindu thought are arranged in ways that are not always intuitively obvious to the Western mind. Instead, concepts of dietary propriety and forms of public duty are combined with epistemological and linguistic explorations.
The Hindu view of the universe most commonly recognizes the presence of the divine within every aspect of the fabric of existence, and this is commingled with the sense of personal connection with individual deities. Consequently, it is impossible to separate right behavior from right forms of thinking.
Hindu philosophical concepts are liberally sprinkled through the verse epics such as the Bhagavad Gita and the Mahabharata, as well as the Vedas, the Upanishads, and other texts, primarily written in the Sanskrit language. Since Sanskrit was considered to be a sacred language and intimately connected with the nature of the universe, issues relating to the language are also considered to be relevant to philosophy.
General philosophical concerns included epistemic, moral, and metaphysical issues. Epistemic concerns are deeply related to the study of the Sanskrit language. It is also concerned with different ways of perceiving and making sense of the universe. Possible forms of interaction included inference, sensory perception, and forms of logical deduction. They also included higher forms of yogic perception of higher spiritual states that were related to the Buddhist concept of enlightenment. Many forms of meditation are involved in the attempt to understand the spiritual nature of the universe.
Moral issues largely centered on the concepts of dharma and karma. The latter relates to the interrelationship between cause and effect and dates from the times of the Upanishads. All acts committed by individuals are morally good or bad, and each will provide good or bad karma, which will attach itself to the individual soul. For the soul to achieve its goal of understanding the nature of the universe it is necessary to accumulate good karma and eliminate bad karma. Philosophers varied as to the efficacy of meditation, good deeds, or actions to attain this understanding. Dharma refers to different methods by which duty should be performed, with respect to both temporal and spiritual obligations. Many of the injunctions on this form of moral behavior are contained in the Dharma Sutras, which are the Vedic-influenced texts that outline various forms of behavior. Some of the many sutras were subsequently developed into shastras, which were used to frame Hindu laws and social regulations, including the caste system.
Metaphysical concerns featured the nature of the divine and how it may be approached. The atman, or the soul, was frequently taken as the unit of analysis. A central metaphysical concern was to understand the specific nature of the atman and how it was related to the wider universe. Some believed that the atman was an intrinsic part of the universe and represented a microscopic but inseparable part of the larger universe. A person who is able to perceive this reality through higher spiritual perception has the opportunity to be freed from the painful cycle of birth and rebirth. However, subsequent developments of thought placed more emphasis on the role of the gods and of divine grace in enabling the atman to
ascend to the higher level of understanding.
Sankara (c. 788–820 c.e.) was a non-dualist of the Advaita Vedanta school and was influential in developing the concept of the atman as being equated with Brahma, which is the universal soul that permeates the entire universe. Since Brahma is not just universal but eternal and eternally unchanging, the atman and the other physical manifestations of the universe are some form of shadow representation of the eternal, and it is possible for the individual, through the cultivation of the faculty of true sight, to attain a glimpse of reality in a process that is very similar to the nirvana of Buddhism.