In his Institutes, Manu says- The Brahmana primarily sprang from the mouth of Brahma. This original Brahmana according to the ordinance married a woman of the same caste, and the offspring of this connection go by the name of Brahmanas. The duties of a Brahmana are celebrating sacrifice, officiating at other's sacrifices, study, teaching, making gifts, and, finally, receiving such. Of these, officiating as priests, teaching and receiving clean gifts are the means of a Brahmana's sustenance; while celebrating sacrifices, study and making gifts are the means of his attaining purity and religious merit. Should a Brahmana fail in maintaining himself and family by the three callings mentioned above, he should then follow such professions proper to Kshatriyas as guarding towns and villages. Should he fail even by such means, he may resort to such professions reserved for the Vaisya caste as cultivating the soil, tending cattle and trading in clean goods. But let him by no means betake himself to callings followed by the Sudras.

The Kshatriya first sprang from the arms of Brahma. The original Kshatriya in accordance with the ordinance married a girl of the same caste, and the offspring of this union are called Kshatriyas. Celebration of sacrifices, study and making gifts are the three duties of a Kshatriya; and bearing arms and defending the subject are his vocation. If a Kshatriya fails in maintaining his family by following the professions mentioned above, he may adopt callings appropriated to the Vaisyas.