Different from that (body) made of mind, more interior, is the Self made of discerning knowledge. By it the former is filled. Faith is its head, cosmic order its right wing, truth its left wing, yoga is its body, mahas its tail and foundation.

This verse presents the fourth kosha: vijñānamaya-kosha, the sheath made of discerning knowledge (vijñāna). It is subtler than the ordinary mind and illumines it.

Vijñānamayaḥ — made of vijñāna. The prefix vi- indicates discernment, discrimination. Vijñāna is the discerning intelligence, the faculty of judgment (buddhi). While manas receives and processes, vijñāna decides, understands, discriminates between the real and the unreal.

The bird structure now comprises elevated spiritual qualities:

• Śraddhā (head) — faith, trust in the teaching and the teacher. Without initial faith, knowledge cannot take root.
• Ṛta (right wing) — cosmic order, natural law. The sage lives in harmony with ṛta.
• Satya (left wing) — truth. Not just not lying, but aligning with reality.
• Yoga (body) — union, the integrating practice. Significantly, yoga is the ātmā, the center, of this sheath.
• Mahas (tail) — greatness, the vastness of knowledge.

It is notable that yoga appears explicitly as the core of the vijñānamaya-kosha. This suggests that yogic practice operates at this subtle level of discernment, not only in body or breath.

The vijñānamaya-kosha is where viveka occurs, the discrimination between the real Self and false identifications. But even the most refined intellect is still a sheath. One more kosha remains, the innermost: the ānandamaya.