ज्ञेयत्वावचनाच्च ॥ ४ ॥
jñeyatvāvacanācca || 4 ||
jñeyatvāvacanāt—Because it is not mentioned (as something) to be known; ca—and.
4. And because it is not mentioned (that the Avyakta) is to be known (it cannot be the Pradhana of the Sankhyas).
Liberation, according to the Sankhyas, results when the difference between the Purusha and the Avyakta (Prakriti) is known. Hence the Avyakta, with them, is to be known. But here there is no question of knowing the Avyakta, and as such it cannot be the Pradhana of the Sankhyas.