Error is false knowledge not based on the true nature of the object.

Viparyaya is the incorrect perception of reality. It occurs when we mistake one thing for another — the classic example is seeing a rope in the dark and believing it to be a snake.

Mithyā-jñānam means false or illusory knowledge. Atad-rūpa-pratiṣṭham indicates that this knowledge is not grounded in the actual form of the object.

This type of error is fundamental in yoga philosophy. Primordial ignorance (avidyā) — mistaking the impermanent for the permanent, the impure for the pure, suffering for happiness, and the not-self for the self — is the root of all suffering according to Patañjali.