Samkhya Karika 18

जननमरणकरणानां प्रतिनियमादयुगपत्प्रवृत्तेश्च ।
पुरुषबहुत्वं सिद्धं त्रिगुण्यविपर्ययाच्चैव ॥१८ ॥

jananamaraṇakaraṇānāṁ pratiniyamādayugapatpravṛtteśca ।
puruṣabahutvaṁ siddhaṁ triguṇyaviparyayāccaiva ॥18 ॥

Janana=birth; maraṇa=death; karaṇānāṁ=of the organs of perception and action; pratiniyamāt=individual allocation; ayugapat=not simultaneous; pravṛtteḥ=from activity; ca=and; puruṣa=Purusha; bahutvaṁ=multiplicity; siddhaṁ=is established; triguṇya=three gunas; viparyayāt=from diverse modification; ca=and; eva=verily

The multiplicity of souls (purusha) is established since birth, death and the instruments of cognition and action are allotted severally; from the non-simultaneity of activities; and from the diverse modifications due to the three gunas.

In the previous few karikas, we have seen the characteristics and attributes of manifest, unmanifest and the Purusha. In this karika, the plurality of purushas is established.

jananamaraṇakaraṇānāṁ pratiniyamāt (from the individual allocation of birth, death and the organs of perception and organs of action): For every birth, there is a combination of the Purusha and a specific grouping of body, eleven sense organs, ego and the buddhi. If there were only on purusha, then all births will happen at the same time, when one dies, all would die etc. If one of the sense organs, for example the ear or the nose, is defective for one, they’d be defective for all the bodies. That, obviously is not the case – hence we establish plurality of purushas.

ayugapatpravṛtteśca (activities don’t happen all at the same time): Activities involving virtue, vice, delusion etc. do not happen simultaneously. One person may carry out virtuous deeds while another may be engaged in non-virtuous deeds and while yet another may be deluded. If there were one purusha only, then everyone would be engaged in identical acts – virtuous, non-virtuous etc. which is not the case. Hence, plurality of purushas is established.

triguṇyaviparyayācca (because of diverse modifications of the three gunas): The commentators don’t seem to provide a satisfactory explanation for this item. The common explanation is as follows:
We notice differences in how the gunas impact different individuals. Some have dominance of sattva guna, others may have more rajas or tamas etc. This would not be the case if there were only one purusha.
The doubt that I have is that even in the case of one individual, the dominance of individual gunas happens constantly. One moment, I am dominated by sattva and engaged in some spiritual study; the next moment, rajas can take over and I may decide to go for a walk, etc. In fact, purusha is totally unaware of the activities of the gunas. The gunas are purely an attribute of the Prakriti and the manifest. So, how can diversity of gunas help establish plurality or otherwise of the purusha? I’d welcome your thoughts.