On Catse system, Apasthamba says thus,
Catvāro varṇā brāhmaṇa kṣatriya vaiśya śūdrāḥ || 4 ||
4. [There are] four castes — brāhmaṇas, kṣatriyas, vaiśyas, and śūdras.
All four are entitled to practice the Dharma set forth by the agreement of the Law-givers.
teṣāṃ pūrvaḥ pūrvo janmataś-śreyān || 5 ||
5. Among these, each preceding [caste] is superior by birth to the one
following.
aśūdrāṇām aduṣṭa-karmāṇām upāyanaṃ vedādhyayanam agnyādheyaṃ
phalavanti ca karmāṇi ||
