The Pātimokkha forms the core of the Vinaya Piṭaka,the first division in the Tipiṭaka,which contains the rules Buddhist monks and nuns must live by. The meaning of the word pātimokkha is unclear, but it may mean something like ‘obligation’ or ‘binding promise.’ The original Pātimokkha was a collection of aphorisms summarising the teachings (D.II,49) but gradually this evolved into a code of behaviour; with 227 rules for monks and an extra 84 rules for nuns. The rules are divided into eight parts according to the severity of the punishment they entail if infringed. The most important of these rules are the four Pārājika, which entail expulsion from the monastic community if broken. They are (1) having sexual intercourse, (2) theft, (3) murder and (4) falsely claiming to have spiritual attainments. Other important rules are the 13 Saṅghādisesa, which if infringed must be confessed. While some of the rules of the Pātimokkha deal with moral issues, most are about etiquette, monastic protocol and behaviour conducive to harmonious communal living, and thus the Buddha said: ‘After I am gone, the monks can if they want change the minor rules.’ (D.II,154). According to the Vinaya, monks and nuns should meet together twice a month to recite the Pātimokkha. See Calendar.