Yoga Sutra - Sādhana Pada 2.22
कृतार्थं प्रतिनष्टंप्यनष्टं तदन्य साधारणत्वात् ॥२२॥
kṛta-arthaṃ prati-naṣṭam-api-anaṣṭaṃ tat-anya-sādhāraṇatvāt ||22||
When [its] purpose is done, it disappears; otherwise it does not disappear due to being common to others.
Although the seen ceases to exist for one whose purpose is accomplished [the liberated puruṣa], it has not ceased to exist altogether, since it is common to other [not-liberated] puruṣas.
This sūtra situates the Yoga tradition as realist (the view that the world is objectively and externally real irrespective of whether we perceive it) as opposed to idealist (the world is not objectively or externally real but a product of the mind); indeed, Dasgupta uses the term “reals” for the guṇas. Patañjali and the commentarial tradition will take some pains to refute the idealist viewpoint in Chapter IV. The “seen” may have accomplished its purpose, kṛta-artha, for the fortunate successful yogī who has attained liberation, and thus may cease to exist, naṣṭam, for such a soul, but only in the sense that the liberated soul ceases to be aware of it; it has not accomplished its purpose for all other puruṣas, says Vyāsa. It needs to provide objects of experience for everyone else. Therefore, it still has a purpose and does not cease to exist, anaṣṭam. Color may not be seen by a blind man, says Vācaspati Miśra, but it does not cease to be, since it is seen by those who are not blind. In this sense, the conjunction between the seers (in the sense of the totality of puruṣas) and the seen is said to be eternal, because the puruṣas are innumerable, so one need not posit the hypothetical possibility that eventually all puruṣas will become liberated, causing prakṛti to become redundant due to an absence of puruṣas needing experience.
This sūtra is important to the Yoga school, Vijñānabhikṣu points out, since otherwise its opponents might question its tenets such as that prakṛti is eternal, creation is ongoing, and Īśvara is eternally sovereign. Moreover, the commentators are motivated by this sūtra to argue the position of the Yoga and Sāṅkhya schools, which posit an eternal plurality of puruṣas, whether in the liberated or nonliberated state, in distinction to the advaita, or nondualist, school of Vedānta, which holds that the plurality and individuality of the puruṣas exist only in the nonliberated state of ignorance. This particular school of Vedānta posits that upon attaining enlightenment, the puruṣa (more typically referred to as ātman by followers of Vedānta) realizes that all plurality and individuality is the product of illusion, and merges into the all-encompassing, nondual, absolute truth, Brahman.
To buttress their view of an eternal plurality of puruṣas scripturally, several commentators point to the verse in the Śvetāśvatara Upaniṣad (IV.5) that speaks metaphorically of a nanny goat (prakṛti), whose nature is that of the guṇas and who produces evolutes of the same nature, being enjoyed by one passionate billy goat (puruṣa) but abandoned by another billy goat who has finished enjoying her. This resonates with Patañjali’s sūtra here. Just because one billy goat may leave the nanny goat, she nonetheless remains to be enjoyed by another billy goat: One puruṣa may become liberated, but all the other unliberated puruṣas remain experiencing prakṛti. Therefore, whether in the liberated or nonliberated states, there must be a plurality of puruṣas, and each one must be individual. This is the view of all six schools of classical Hindu thought except the subbranch of the Vedānta school, advaita Vedānta.