Ṛgveda-Prātiśākhya Chapter 6 (Dhvanyāgama-paṭala) (6.1-55)

6.1 The first (letter) of a conjunct consonant, when preceded by a vowel or Anusvara , and occurring where there is no unchanged Visarjanīya (avikrama), is uttered twice. This is called ‘doubling’ (krama).

Examples:

agnim > aggnim RV 1.1.1

Note: Not shown in the printed texts

6.2 An aspirate, however, is once uttered together with its preceding (i.e., unaspirated consonant).

Examples:

abhrāteva > abbhrāteva RV 1.124.7

Note: Not shown in the printed texts

6.3 Ch (is, thus once uttered together with its own preceding or unaspirated consonant), even if not at the beginning of a conjunct consonant.

Examples:

kavi-chadā > kavicchadā RV 3.12.3

pari-chinnāḥ > paricchinnāḥ RV 7.33.6

pṛthu | chardiḥ > pṛthu cchardiḥ RV 1.48.15

6.4 (A consonant) which follows r is doubled.

6.5 Similarly a contact consonant following l (is doubled).

6.6 (A contact consonant) following an Ūṣman (is) optionally (doubled).

6.7 A final consonant (following r is) not (doubled).

6.8 R (is) not (doubled).

6.9 An Ūṣman, which is part of a conjunct consonant and is not preceded by any letter, (is) optionally (doubled).

6.10 But not an Ūṣman followed by a vowel or an Ūṣman.

6.11 Nor a (consonant) preceding a doubled consonant.

6.12 (Nor) an initial ch, if preceded by the words saha, atihāya, pavamāna, yasya and the two words tane ca.

Examples:

saha-chandasaḥ > sahachandasaḥ RV 10.130.7

ati-hāya | chidrā > atihāya chidrā RV 1.162.20

pavamāna | chandasyām > pavamāna chandasyām RV 9.113.6

yasya | chāyām > yasya chāyām RV 10.121.2

6.13 (Nor when it is preceded) by a long vowel excepting mā.

Examples:

vṛṣā | chanduḥ > vṛṣā chanduḥ RV 1.55.4

mā | chedma > mā cchedma RV 1.109.3

6.14 (Nor an initial) consonant joined to another consonant (and following a long vowel) according to the teaching of Śākalya.

6.15 ṅ and n occuring at the end of a word and preceded by a short vowel are doubled, if a vowel follows.

(short vowel)ṅ + vowel = (short vowel)ṅṅ + vowel

(short vowel)n + vowel = (short vowel)nn + vowel

Note: Short vowels are a, ṛ, i, and u. In Ṛgveda only aṅ, ṛṅ, iṅ, an, and in appear at the end of a word.

Examples:

dadhyaṅ | ṛṣiḥ = dadhyaṅṅṛṣiḥ (RV 6.16.14)

sadṛṅ | asi = sadṛṅṅasi (RV 1.94.7)

hiṅ | akṛṇot = hiṅṅakṛṇot (RV 1.164.28)

ketum | kṛṇvan | aketave = ketuṁ kṛṇvannaketave (RV 1.6.3)

vṛṣan | agne = vṛṣannagne (RV 10.191.1)

yasmin | indraḥ = yasminnindraḥ (RV 1.40.5)