Louis Dumont, in his seminal work 'Homo Hierarchicus: The Caste System and Its Implications,' posited that the Indian caste system is fundamentally structured around a single, overarching binary opposition: the pure and the impure. This opposition is not merely a social distinction but a religious one, forming the ideological bedrock of the entire hierarchical system.

According to Dumont, the concept of purity and impurity is central to understanding the caste system's logic. The Brahmins, at the apex of the hierarchy, embody the highest degree of purity, primarily through their ritual functions, vegetarianism, and adherence to specific codes of conduct. Conversely, the Dalits (formerly 'untouchables') are relegated to the lowest rung due to their association with occupations deemed ritually polluting, such as handling dead bodies, leatherwork, or scavenging. This binary opposition dictates social interactions, occupational divisions, and even spatial segregation within villages.

This pure/impure dichotomy is not static but dynamic, manifesting in various aspects of daily life. For instance, food preparation and consumption are heavily influenced by purity norms, with specific castes having restrictions on what they can eat and from whom they can accept food. Marriage is strictly endogamous within castes, primarily to maintain the purity of lineage. Occupations are traditionally hereditary and ranked according to their perceived ritual purity or impurity, reinforcing the hierarchical structure. Even physical proximity is governed by this opposition, with lower castes historically being denied access to temples, wells, or even certain streets used by upper castes.

Dumont argued that this religious hierarchy of pure and impure subsumes and encompasses all other forms of social stratification, including economic and political power. While critics have pointed out that Dumont's emphasis on ritual purity overlooks the significant role of power and economic exploitation in maintaining the caste system, his concept of binary opposition remains a powerful analytical tool for understanding the ideological framework and the enduring resilience of caste hierarchy in India. It highlights how a fundamental distinction, rooted in religious beliefs, can permeate and organize an entire social structure, shaping individual identities and collective relations.