The English sound “y” (IPA [j]) is written with the letter “i” in Sindarin (LotR/1114). This convention is necessary because “y” ([y]) represents a vowel in Sindarin. According to Tolkien, the letter “i” only represents the y-sound when it appears at the beginning of a word before a vowel, for example in the name Ioreth (pronounced “Yoreth”). Otherwise, the letter “i” represents the vowel [i].

This Sindarin writing convention resembles Welsh, which also uses “i” for both the y-sound and i-sound. In Welsh, however, an “i” can represent a y-sound when it appears before a vowel anywhere in the word, not just at the beginning (in particular, between a consonant and a vowel). Tolkien’s description of Sindarin spelling implies that [j] only survived at the beginning of words in Sindarin, and became the vowel [i] elsewhere.