Kalpa texts give very long explanations of the ritualistic forms in the Brāhmaṇa texts. The Kalpasūtra is classified under four heads – 1) Srautasūtra 2) Gṛhyasūtra 3) Dharmasūtra and 4) Śulbasūtra. The first treat the worship of the Agni, and performance of Yajñas like Darśapūrnamasa and Somayaga. The second type of Kalpasūtra texts deal with the ceremonies included in sixteen Samskaras (Sodaśasamskara, 16 rituals taking place in the curse of human life), the duties of Brahmacari (1st Vedic age), Gṛhasta (2nd age, family), the explanations about Pancamahāyajñas etc. The third deal with the rules, laws, religious customs and their usage and the duties of the Caturvarṇas (4 social categories), etc. The Śulbasūtra are manuals which help on in constructing Vedis, Yāgakuṇḍas, altars, Yajñasālas so on.