When the Portuguese began to trade extensively with South Asia, they quickly noticed a fundamental difference between South Asian societies and those of other world areas. In India and Sri Lanka, societies are broken up into a large number of groups who do not intermarry, who are ranked in relation to eaÍÍÍch other, and whose interactions are governed by a multitude of ritualized behaviors. The Portuguese called these groups casta, from which the English term caste is derived. In South Asia, they are described by the term jati, or birth. According to traditional culture, every person is born into a particular group that defines his or her unchangeable position within society.

One of the most basic concepts underlying caste is purity. On one level this idea translates into a concern for personal hygiene, but the concept ultimately refers to a psychic or spiritual purity that lies beyond the physical body. A religious interpretation associated with Indian thought asserts that personal salvation or enlightenment is the ultimate goal of life, and that the individual goes through many lives and experiences before attaining sufficient knowledge to transcend the material world. Those beings who have gone farther on this road to enlightenment have purified their consciousness and regulate their lives in order to prevent more gross experiences from interfering with their progress toward salvation. Those groups of people whose life-styles are the purest are farthest along on the spiritual road and are most deserving of respect. These ideas about purity offer a rationale for dividing society into a large number of groups, ranked according to the purity of their lifestyles or occupations. The persons in each group must be careful to preserve the relative purity of their own group and to avoid close contact with persons of lower purity otherwise, they may sully or "pollute" themselves or the members of purer groups.

The idea of psychic purity blends with a series of traditional notions about pure or polluting substances and about behaviors and rituals, resulting in a rich system that explains caste segregation and modes of caste interaction. It is possible for people to transmit their qualities to others by touching them or by giving them objects. In extreme cases, even the shadow of a very low-caste individual can pollute an individual of the highest, priestly castes. If the physical contact is intimate or if people have manipulated certain objects for a long time, the intensity of the transmitted qualities increases. Simple objects such as tools, for example, may change hands between persons of different caste without problem. Food, however, which actually enters and becomes part of a person's body, is a more serious matter. Cooked food, involving processing and longer periods of contact, is more problematic than uncooked food. There is thus a series of prohibitions on the sharing of food between members of different castes. Members of higher castes may avoid taking food from members of lower castes, although lower-caste persons may not mind taking food fro cf9 m memberss of the higher orders. The most intimate contact is sexual because it involves the joining of two bodies and the transmission of the very substances that determine caste for life. Sexual contact between persons of different castes is discouraged, and intercaste marriage is rare. When intercaste sexual affairs do occur, they are almost always between men of higher caste and women of lower caste, for it is less polluting to send forth substances than to receive them. In the distant past, women who had sexual contact with men of lower caste were killed, and they would still be ostracized today in some villages. When polluting contacts occur between members of different castes, personal purity may be restored by performing cleansing rituals. In general, these concepts of purity prevent partaking of meals together and intermarriage between different castes, regulate intercaste relations through a wide variety of ritual behaviors, and preserve deep-seated social cleavages throughout Sri Lanka.

There has been a strong tendency to link the position of different castes in the social hierarchy to their occupations. Groups who wash clothes or who process waste, thus coming in contact with undesirable substances from many persons, are typically given low status. In both Hindu and Buddhist thought, the destruction of life is very ignoble, because it extinguishes other beings struggling for consciousness and salvation. This idea has rationalized views of fishermen or leather workers, who kill animals, as low and impure groups. In many cases, however, the labeling of an occupational group as a caste with a particular status has depended on historical developments rather than theories of purity. As the village farming economy spread over time, many tribal societies probably changed from hunters and gatherers to low-status service castes, ranked below the landowning farmers. Many poor agricultural laborers in Sri Lanka remain members of low castes as well. Other immigrant groups came to Sri Lanka, fit into particular occupational niches, and became known as castes with ranks linked to their primary occupations. Castes with members who accumulated wealth and power have tended to rise gradually in their relative positions, and it is not uncommon for members of rising caste groups to adopt vegetarianism or patronize religious institutions in an attempt to raise their public ritual status.

Data as of October 1988