Why do bhikkhunis follow more precepts (sikkhapada) than monks?

In Theravada, monks follow 227 precepts and bhikkhunis follow 311 precepts. This difference often leads to misunderstanding that the Buddha in fact did not want women to join the Order, and so he set up rules as barrier to fence off women right at the start.

From a comparative study between the monks and nuns patimokkha (presented at an International Conference on Thai Studies, Chiengmai, Oct. 1417, 1996) it is shown that counting by section, bhikkhus observe eight sections as compared to seven sections by nuns. One section exclusively for monks is called "Aniyata." In this section, there are two rules introduced by Visakha, the leading female lay supporter in early Buddhism. One of them forbids the monks from staying alone with a female in a covered place and another one forbids monks from staying alone with a female in an open place beyond hearing of others.

In Parajika, the first section of the patimokkha which is concerned with the most severe offences, any monk or nun who has transgressed any one of these rules is "defeated" at the moment of committing that act. There are four rules for monks and eight rules for nuns. The extra rules that nuns have to observe in this section may be found for monks also but are classified under Sanghadisesa, the second section which is less severe. Having transgressed it a monk will have to go through 'manatta' period, a temporary self-expulsion from the Sangha. It is worth noting that classification of the rules can easily be the work of a later period at the hands of the monks.

In Patidesaniya section, there are eight rules for bhikkhunis. Bhikkhus have the same content of the rules but they are counted as one and classified under Sekhiya, another section. This is one of the reasons responsible for the bloated number of rules for bhikkhunis.

In the Pacittiya section, bhikkhunis follow 166 rules as compared to 92 for bhikkhus. There are 70 common rules shared by both Sanghas. Then bhikkhus have another set of 22 exclusively for bhikkhus and bhikkhunis have another set of 76 rules exclusively for bhikkhunis. Within 76 rules exclusively for bhikkhunis, it is notable that there are many rules regarding ordination requirements which the bhikkhus also have to follow, but for bhikkhus they are not counted in the Patimokkha. This also results in a seemingly larger number of Patimokkha rules for bhikkhunis.

Due to the above reasons, the bhikkhunis carry a higher number of rules in the Patimokkha than the monks, but in reality they follow a similar set of rules.