Sociolinguistic research in India is the study of how the Indian society affects and is affected by the languages of the country. India is a highly multilingual nation, where many languages are spoken and also studied, both as part of linguistics and with the aim of aiding community development. Though theoretical and comparative linguistics have a long history in the country (dating back to perhaps the first millennium BCE), few researchers have concentrated on the sociolinguistic situation of India. Context India is a particularly challenging and rewarding country in which to conduct sociolinguistic research due to the large number of languages spoken in the country (415 are listed in the SIL Ethnologue). History of sociolinguistic research Variation between Indian languages has been noted for millennia: by Tolkāppiyar (Tamil) in his "Tolkāppiyam"(5 BCE);Yaska in his Nirutka (500 BCE); Patanjali (200 BCE); Bharata in his Natyasastra (500 CE);and Abu'l-Fazl ibn Mubarak in his Ain-e-Akbari (16th century). The classification of languages, particularly with regard to regional differences and to so-called 'hybrid' languages, continued to progress during the 19th century. From 1881, language information was explicitly sought in the census, which found a total of 162 languages in the country (116 Indian languages and 46 foreign languages). Questions about language continued to be included in the 10-yearly census in the following years, and in 1896 George Abraham Grierson began his Language Survey of India, in which he tried to classify Indian languages based on the distribution of morpho-phonemic differences. Jules Bloch published a study on caste dialects in 1910, however this was not followed up for some decades. Early Indian research into sociolinguistics can be said to have begun in the early 1960s. Charles A. Ferguson published Diglossia (1959) on variation as a developmental and functional phenomenon of language, while John J. Gumperz published on the linguistic aspects of caste differentiation in 1960. Both topics were quickly picked up by Indian linguists. In the mid-1960s, William Labov added an interest in variation within the speech of a caste. A seminar on "Language and Society in India" was held in 1967 and in 1969 the Central Institute of Indian Languages was founded, which had a particular success into drawing young linguists into applied studies. In 1972 the University of Delhi introduced the first sociolinguistics course. Almost a hundred years after Grierson's survey, the International Centre for Research on Bilingualism completed its sociolinguistic Survey of India