 According to Sāṃkhya philosophers, the relation between prakṛti and puruṣa in an individual person is said to be eternal and irresolvable. This raises a problem for the Sāṃkhya, namely, how are we to explain the bondage (coming together) of prakṛti and puruṣa (soul), and how is the final release liberation of puruṣa possible? The clue lies in understanding the process of evolution. Verse 21 of the Sāṃkhya-kārikā offers a succinct answer: