In nature there are gross manifestations and subtle ones. The gross manifestations are perceived by the senses, as they are only effects of the real cause – the subtle ones. Almost all systems of knowledge in India aim at knowing the subtle perceptions. For this purpose they resort to ‘Yoga’ as a fundamental method.

To explain what is Yoga, Katha Upanishad says:
Tam Yogam - eti manyante sthiram indriya dharanam
Apramattas - tada bhavati, yogo – hi prabhavapyayau

The highest state is that, they say, when the five senses of knowledge, together with the mind cease from their normal activities and the intellect itself does not stir.

The ancient seers realized that the reason for all human miseries is the wrong conception of the passive self to be the active and the real one, which is the Atman. Upanishads are the oldest authority, which advocate yoga as the right path to be chosen for the knowledge of the Real Self (Atman).