व्यत्ययो बहुलम्

In the छन्दस् (Vedas) there is diversely an interchange of the various विकरण-as शप् etc. which have been previously ordained under special circumstances.
The word व्यत्यय means transgression of the fixed rule, or interchange, taking of two vikaraņas at a time, and so on. Thus भेदति = भिद + शप् + ति) instead of भिनत्ति from the root भिद 'to split', belonging to the Rudhadi class; e.g. शुष्मस्य आण्डानि भेदति (Rig. VIII.40. II.) 'He (Indra) break the eggs (children) of Shushma; so also, जरसा मरते पतिः (Rig. X. 86. II); here there is मरते = (मृ + शप् + ते) instead of म्रियते; the root मृ belonging to the Tudadi class. So also there are two vikaraņas at one and the same time, in the following. इन्द्रो वस्ते न नेषतु 'May Indra lead by this abode' ; here there is नेषतु 3rd. per. sing. of the Imperative लोट् of the root नो 'to lead' ; there are two vikaraņas सिप् and शप् instead of नयतु = (नी +शप् + त्); इन्द्रेण युजा तरुषेम वृत्रम् (Rig. VII.48. I). The word तरुषेम (तृ + उ + सिप् + शप् + अम) is the Ist. per. sing. of the )Optative (लिङ्) of the root तृ, the classical form being तरेम or तीर्याम 'may we cross'.

In the Vedic literature we have many apparent irregularities with regard to the rules of declension of nouns, conjugation of verbs, application of Parasmaipada or Atmanepada affixes; rules of gender, person or tense, rules of interchange of consonants, or of vowels, rules of accent, rules relating to कृत् and तद्धित affixes and rules relating to the affixes included in the pratyahara यङ् 3.1.22 to 3.1.86.