According to Hinduism, man is essentially a soul that uses its body and mind as instruments to gain experience. What is the nature of the soul? Hinduism maintains that the macrocosm and the microcosm are built on the same plan, and that Brahman is the soul of both. As the soul of man, Brahman is known as Paramatman. The Upanishads speak of the two souls of man dwelling, as it were, side by side, within him: the real soul (Paramatman) and the apparent soul (jivatman). The real soul is the witness consciousness, serene and detached. The apparent soul is the embodied soul, the experiencer of birth and death, and is ever in quest of freedom and eternal life. The apparent soul is the ego self--the reflection of the real soul. The real soul has been described as Self and the apparent soul as non-Self. Hinduism analyzes man in terms of three bodies, five sheaths, and three states. It says that a human individual has three bodies: physical body, subtle body, and causal body. The physical body is produced out of the gross forms of the five basic elements (ether, air, water, fire, and earth), and is subject to a sixfold change: birth, subsistence, growth, maturity, decay, and death. At death the physical body perishes and its five constituent elements are dissolved. The subtle body is made of the subtle forms of the five basic elements that produced the physical body. It is the receptacle of thoughts and memories and continues to exist after death, serving as the vehicle of transmigration. A human individual enters this world with a bundle of thoughts in the form of his mind, and he also exits with a bundle of thoughts, some old and some new. The causal body, characterized by ego sense only, is finer than the subtle body. All three bodies are for the fulfillment of desires, gross and subtle. The soul is different from these three bodies.
Hindu scriptures further describe the body-mind complex of man as consisting of five sheaths, or layers: the physical sheath, the sheath of prana (the vital air), the sheath of mind, the sheath of intellect, and the sheath of bliss. These sheaths are located one inside the other like the segments of a collapsible telescope, with the sheath of the physical body being the outermost and the sheath of bliss being the innermost. The sheath of the physical body is dependent on food for its sustenance and lasts as long as it can absorb nourishment. The sheath of the vital air is the manifestation of the universal vital energy. It animates the gross body, making it inhale and exhale, move about, take in nourishment, excrete, and reproduce. The sheath of the mind is the seedbed of all desires. It is changeful, characterized by pain and pleasure, and has a beginning and an end. The sheath of the intellect is the seat of I-consciousness. Though material and insentient by nature, it appears intelligent because it reflects the light of the Self. It is the cause of embodiment. Finer than the sheath of the intellect is the sheath of bliss, the main features of which are pleasure and rest. It, too, is material and subject to change. The five sheaths are the five layers of embodiment and they veil the light of the Self.
The Upanishads mention that man experiences three states of existence-waking, dream, and deep sleep-and his Self within, the experiencer of the three states, is different from them. Analysis of all three states reveals the true nature of the Self. In the waking state man remains identified with his physical body, in the dream state with his subtle body, and in deep sleep with his causal body. The Atman, or Self, is the monitoring consciousness of all three states and is the basis of their unity. Hinduism contends that conclusions based only on an analysis of the waking state are incomplete and cannot reveal the real nature of man. In this sense, Hinduism considers the conclusions of physical science as inadequate although not incorrect.