The breath is the one autonomic process handed to the will — the lever between body and mind.
The Fourth Limb
With the seat established, Patanjali turns to the breath. Pranayama is usually parsed as prana (vital energy, of which breath is the coarsest expression) plus ayama (extension, expansion) — the extension of the life-force, regulated through the breath that carries it. The Sutras define it as the cutting off of the flow of inhalation and exhalation once posture is secured (II.49), and describe its variables with an engineer's economy: external, internal, and suspended operations, measured by place, time, and number, becoming progressively long and subtle (II.50). A fourth kind transcends the inner and outer entirely (II.51).
Patanjali's claim for the practice is large: pranayama destroys the covering of the inner light (II.52), and by it the mind becomes fit for concentration (II.53). The breath is the hinge of the whole system — the only vital function that runs automatically yet answers immediately to conscious control. Agitate the mind and the breath shortens; lengthen the breath and the mind settles. Pranayama works that hinge deliberately, using the one process available to both wills to bring the involuntary life under the influence of the voluntary.
Practice
The later Hatha tradition built an extensive pharmacopoeia of techniques — alternate-nostril breathing (nadi shodhana), the bellows breath (bhastrika), the victorious breath (ujjayi), retention (kumbhaka) in its many ratios. In the subtle-body physiology those texts assume, the breath moves prana through the channels (nadis) and centres of the energetic anatomy mapped in the Chakras, purifying the central channel so that the coiled energy at the root can rise — the territory of Kundalini & Tantra. Patanjali needs none of that machinery for his purpose; for him the outcome is simply a mind made quiet, clear, and fit for what comes next. The practical instruction underneath every technique is the same: make the breath long, smooth, and subtle, and the mind will follow it down.
Place in the Sequence
Pranayama completes the outer limbs. Behind it lie conduct (Yama, Niyama) and body (Asana); ahead lies the decisive turn. Having quieted the world, the body, and the breath, the practitioner next withdraws attention from the senses altogether — Pratyahara, the fifth limb, the doorway between the outer work and the inner.
Related
- Eight Limbs of Yoga — the sequence
- Asana — the previous limb, the seat
- Pratyahara — the next limb, withdrawal
- Chakras — the subtle anatomy the breath moves through
- Kundalini & Tantra — where the energetic reading of breath-work leads
- Yoga — the parent overview