One who is in a lower grade of social life cannot accept the profession of a higher class unless necessary. In times of emergency, all the classes but the kṣatriyas may accept professional duties of others. The means of livelihood known as ṛta (śiloñchana), amṛta (ayācita), mṛta (yācñā), pramṛta (karṣaṇa), and satyānṛta (vāṇijya) may be accepted by everyone but the kṣatriyas. For a brāhmaṇa or a kṣatriya, engaging in the service of the vaiśyas or śūdras is considered the profession of dogs.