The socio-linguistic situation of Tamil is characterised by diglossia: there are two separate registers varying by social status, a high register and a low one. Tamil dialects are primarily differentiated from each other by the fact that they have undergone different phonological changes and sound shifts in evolving from Old Tamil. For example, the word for “here”—iṅku in Centamil (the classic variety)—has evolved into iṅkū in the Kongu dialect of Coimbatore, inga in the dialect of Thanjavur, and iṅkai in some dialects of Sri Lanka. Old Tamil’s iṅkaṇ (where kaṇ means place) is the source of iṅkane in the dialect of Tirunelveli, Old Tamil iṅkaṭṭu is the source of iṅkuṭṭu in the dialect of Madurai, and iṅkaṭe in various northern dialects. Even now, in the Coimbatore area, it is common to hear “akkaṭṭa” meaning “that place”. Although Tamil dialects do not differ significantly in their vocabulary, there are a few exceptions. The dialects spoken in Sri Lanka retain many words and grammatical forms that are not in everyday use in India, and use many other words slightly differently. According to Kamil Zvelebil, the Tamil dialects can be segregated on the following ‘Centers of Prestige’: Madras Tamil, Madurai Tamil, Kongu Tamil, Nellai Tamil, Kanyakumari Tamil, Thanjavur, Tiruchirappalli Tamil, Jaffna or Yazhpanam Tamil, Trincomalee or Tiriconamalai Tamil, Batticaloa or mattakkalappu Tamil.
The dialect of the district of Palakkad in Kerala has a large number of Malayalam loanwords, has also been influenced by Malayalam syntax and also has a distinct Malayalam accent. Similarly, Tamil spoken in Kanyakumari District has unique words and phonetic style than Tamil spoken at other parts of Tamil Nadu. The uniqueness of words and phonetics is such that someone from Kanyakumari district is easily identified by the spoken Tamil. Hebbar and Mandyam dialects, spoken by groups of Tamil Vaishnavites who migrated to Karnataka in the 11th century, retain many features of the Vaishnava paribasai, a special form of Tamil developed in the 9th and 10th centuries that reflect Vaishnavite religious and spiritual values. Several castes have their own sociolects which most members of that caste traditionally used regardless of where they come from. It is often possible to identify a person’s caste by their speech. Tamil in Sri Lanka incorporates loan words from Portuguese, Dutch, and English.