Karika 18

जननमरणकरणानां प्रतिनियमादयुगपत्प्रवृत्तेश्च। पुरुषबहुत्वं सिद्धं त्रैगुण्यविपर्ययाच्चैव ॥१८॥

jananamaraṇakaraṇānāṁ pratiniyamādayugapatpravr̥ttēśca। puruṣabahutvaṁ siddhaṁ traiguṇyaviparyayāccaiva ॥18॥

[जनन मरण करणानां प्रति नियमात् अयुगपत् प्रवृत्तेः च। पुरुष बहुत्वं सिद्धं त्रैगुण्य विपर्ययात् च एव॥
janana = birth; maraṇa = death; karaṇānāṁ = the cause of; prati = of each; niyamāt = by law; ayugapat = not being simultaneous; pravr̥ttēḥ = tendencies; ca = and; puruṣa = of Purusha; bahutvaṁ = multiplicity; siddhaṁ = established; traiguṇya = three qualities; viparyayāt = from deformations; ca = and; ēva = as well;]

The birth and death of each (person) by law is not simultaneous as its cause is driven by tendencies resulting in deformations of the three qualities. Hence (as it is not simultaneous), the multiplicity of the Purusha is established.

Each individual soul differs from the other as birth and death of individuals do not happen simultaneously.