Ida

The nadis are, in the yogic and tantric physiology of India, the channels through which the vital energy, prana, flows in the subtle body; the texts speak of thousands of them, but three are principal, and Ida is one of the two that spiral around the central channel. Ida is the lunar channel, cool, receptive and associated with the left side, with the moon, with the parasympathetic calming functions and with the mental and introspective aspects of the self.

In the classic description it winds from the base of the spine up to the region of the left nostril, crossing the central Sushumna and alternating with its solar counterpart Pingala at the energy centres. The breath is said to flow more strongly through one nostril and thus one channel at a time, alternating through the day, and much yogic breath-practice aims to balance the two so that energy can enter the central channel. The nadi doctrine is ancient, part of the tantric and hatha-yoga subtle anatomy set out in texts such as the Hatha Yoga Pradipika.

Nadi shodhana, alternate nostril breathing, is the practice most directly built around Ida and Pingala: the practitioner closes the right nostril and breathes through the left, Ida's channel, then closes the left and breathes through the right, Pingala's, in an alternating sequence said to balance the lunar and solar currents and prepare the subtler central channel, Sushumna, to open. Ida's opening at the left nostril is why left nostril dominant breathing is traditionally read as a lunar, cooling, introspective state in yogic physiology.

Where Ida, Pingala and Sushumna are said to cross is marked by a granthi, a psychic knot, most notably at the base of the spine, the heart and the point between the eyebrows, and yogic and tantric texts describe these crossing points as the sites kundalini energy must pass through as it rises.

Nadis are sometimes compared to the meridians of Chinese medicine because both describe channels carrying a vital force through the body, but the two are independent systems from separate traditions with different maps, different numbers of channels and different diagnostic uses, and treating one as a translation of the other rather than as a parallel, historically unconnected framework is a conflation the sources themselves do not support.

Sources The Serpent PowerSir John Woodroffe (Arthur Avalon) with Roots of YogaJames Mallinson and Mark Singleton (trans. and eds.)