In two interconnected theoretical works published in 1962, Lévi-Strauss argued that the tendency among primitive societies to formulate animal classification systems and to express these systems ritually cannot be explained as a side-effect of social classification, as Durkheim and Mauss had argued, nor can it be explained on the narrow materialistic grounds posited by Radcliffe-Brown and Malinowski. The negative evidence adduced by Lévi-Strauss is empirical: animal classification systems are neither limited to societies in which there exists a fixed correlation between social groups and animal species, nor do they pertain to species that are of significant material or symbolic value to the classifying culture. According to Lévi-Strauss, the ritual expression of the mental act of classification functions like a language, containing “stressed” and “unstressed” elements and aiming to convey theoretical messages.