Much of Tamil grammar is extensively described in the oldest available grammar book for Tamil, the Tolkāppiyam (dated between 300 BCE and 300 CE). Modern Tamil writing is largely based on the 13th century grammar Naṉṉūl, which restated and clarified the rules of the Tolkāppiyam with some modifications. Parts of Tamil grammar Traditional Tamil grammar consists of five parts, namely eḻuttu, sol, poruḷ, yāppu, and aṇi. Of these, the last two are mostly applicable in poetry. The following table gives additional information about these parts. Eḻuttu (writing) defines and describes the letters of the Tamil alphabet and their classification. It describes the nature of phonemes and their changes with respect to different conditions and locations in the text. Sol defines the types of the words based on their meaning and the origin. It defines the gender, number, cases, tenses, classes, harmony, etc. This chapter also provides rules for compounding the words. Porul defines the contents of poetry. It gives guidance on which topic to choose for poetry based on certain conditions like the nature of the land or time or the people. It gives a distinction between Agam (Internal / love life) and Puram (external / worldly life). Yāppu defines rules for composing Traditional poetry. It defines the basic building block Asai and describes how asai should be joined to form a sīr, joining sīr for an adi. Aṇi defines techniques used for comparing, praising and criticizing the taken topics. Letters The script of Tamil Language consists of 247 letters. The script falls under the category Abugida, in which consonant-vowel sequences are written as a unit. The grammar classifies the letters into two major categories. Prime Letters – Dependent Letters – Prime Letters 12 vowels and 18 consonants are classified as the prime letters. The vowels ( ): அ (a), ஆ (ā), இ (i), ஈ( ī), உ (u), ஊ (ū), எ (e), ஏ (ē), ஐ (ai), ஒ (o), ஓ (ō), ஔ (au) The consonants ( ): க், ங், ச், ஞ், ட், ண், த், ந், ப், ம், ய், ர், ல், வ், ழ், ள், ற், ன் The vowels are called uyir, meaning soul, in Tamil. The consonants are known as mey, meaning body. When the alphasyllabary is formed, the letter shall be taking the form of the consonants, that is the body, and the sound shall be that of the corresponding vowel, that is the soul. The vowels are categorized based on