Chandas-shastra is one of the six vedA~Nga, the others being shIksha, vyAkarana, kalpa, nirukta and jyotisha. This shAstra deals with poetic meters – the rhythmic structure of a verse. There are three types of vedic mantras – verse mantras called R^iks, prose mantras called yajushes and tunes called sAmans. These are not to be confused with the actual vedas as a veda may contain more than one type of mantra. Yajurveda contains lot of R^ik mantras and atharvaveda contains both Rik and Yajur mantras. Samaveda contains sAmans based on R^ik mantras and its brAhmaNa texts contain yajur mantras to be used in somayAga.
Chandas or meter is an inherent property of a verse and hence a knowledge of this shastra enables one to appreciate the rhythmic structure of verse mantras in all the four vedas. Some examples of meters are gAyatri, jagatI, triShTubh, anuShTubh, bR^ihati etc. A perceptive reader would immediately point out that poetic meter is not a unique property of vedic verse mantras but seen in laukika literature too. Moreover, there are numerous meters seen in laukika literature that are not found in the vedas. KalidAsa has employed vedic meters like gAyatrI and triShTubh in his kAvyas. If so, why is this shastra reckoned as a vedA~Nga? Surely, poetry appreciation is not the sole reason for this reckoning. We will see in subsequent sections that just like other vedA~Ngas a knowledge of Chandas is also important for the correct performance of a yaGya.
Discussion on vedic meters can be found in texts like R^ik prAtishAkhya, nidAna sUtra and AshvalAyana shrautasUtra. The earliest treatise that formally treats Chandas that survive today are the sutras of Pingala. He is known as pi~NgalAchArya or pi~NgalanAga. Who he was and when he lived are some questions for which we probably won’t satisfactory answers. There is a story about him being a “nAga” – a snake and once he was threatened by an eagle. He enters a wager with it that the eagle should recreate a text he composes on meter and eventually wins. This story is obviously in the realm of mythology. This text deals with both vedic and non-vedic meters.
Some of the commentaries of this text are vR^iktoktiratna of bhaTTanArAyaNa and pi~NgalaprakAsha of vishvaratha. Both of these are lost. The surviving commentary is a vritti of halAyudhabhaTTa called mR^itasa~njIvani. We learn a little about halAyudha from his work called brAhmaNasarvasvaM. He was an erudite scholar and received the title of “rAjapaNDita” from King lakshmanasena when he was twelve, minister post when he was a youth and finally received the “dharmAdhikAri” post later in life. Lakshmanasena belonged to the Sena or Sen dynasty who ruled from around 1179 CE till his expulsion in 1202 by Bakthiar Khalji. He moved to East Bengal and ruled for three more years till his death. Apparently, apart from Halayudha, Jayadeva of Gitagovindam fame also adorned Lakshmanasena’s court.
Halayudha also authored other texts like paNDitasarvasvaM, shivasarvasvam, nyAyasarvasvam, matsyasUkta tantram, abhidhAnaratnamAlA and kavirahasyam. Right at the beginning, Halayudha quotes a ChAndogya brAhmaNam to the effect of “whomsoever officiates in a yaGya or teaches the mantras without the knowledge of R^ishi-Chandas-devata becomes a sinner, falls into hell and perishes” and declares one should necessarily learn and understand the Chandas shastra.