When the root word 'kitap' (book) is followed by the accusative case suffix, what is the correct form, and what vowel harmony principle is demonstrated?

When the root word 'kitap' (book) is followed by the accusative case suffix, the correct form is 'kitabı'. This demonstrates the vowel harmony principle of backness. Vowel harmony is a phonological rule in Turkish where vowels within a word tend to agree in certain characteristics. Backness refers to the position of the tongue when producing a vowel; back vowels are produced with the back of the tongue raised, while front vowels are produced with the front of the tongue raised. The root word 'kitap' contains the vowels 'i' and 'a'. 'i' is a front vowel, and 'a' is a back vowel. The accusative case suffix in Turkish has four forms: -ı, -i, -u, -ü. The specific form chosen depends on the last vowel of the root word. When the last vowel of the root word is a back vowel ('a' or 'u'), the suffix vowel is also a back vowel. In 'kitap', the last vowel is 'a', which is a back vowel. Therefore, the accusative suffix vowel must also be a back vowel. Among the options -ı, -i, -u, -ü, the back vowel that matches the quality of the last vowel 'a' is 'ı'. So, 'kitap' + '-ı' becomes 'kitabı'. If the last vowel were a front vowel, a front vowel suffix would be chosen (e.g., if the word were 'ev' (house), the accusative would be 'evi', using the front vowel suffix '-i' because 'e' is a front vowel).