What is the difference between "ゐ" and "い", "ゑ" and "え"?

The difference between the kana "ゐ" and "い," and "ゑ" and "え," is fundamentally one of historical orthography versus modern usage, representing a pivotal simplification in the Japanese writing system. In classical Japanese, these characters represented distinct phonetic values: "ゐ" (wi) and "ゑ" (we) were used for syllables that began with a semi-vowel /w/ sound, while "い" (i) and "え" (e) represented pure vowel sounds. This distinction was phonologically meaningful in earlier stages of the language, much like how English once distinguished letters now silent. However, the critical point is that this phonetic distinction has been entirely lost in modern standard Japanese pronunciation. Through a process of sound change, the /w/ sound before the vowels /i/ and /e/ eroded, causing "ゐ" and "い" to merge in pronunciation as /i/, and "ゑ" and "え" to merge as /e/. Consequently, the characters became homophonic, rendering the older kana functionally redundant for representing contemporary speech.

The official resolution to this redundancy came through orthographic reforms in the mid-20th century. The modern kana usage guidelines, established after World War II, mandated that the sounds /i/ and /e/ be written exclusively as "い" and "え." The characters "ゐ" and "ゑ" were formally declared obsolete for general use and removed from the standard kana syllabary. This reform was part of a broader effort to simplify Japanese orthography and make literacy more accessible. Therefore, in all contemporary writing—from government documents and newspapers to everyday correspondence—only "い" and "え" are employed. The historical kana "ゐ" and "ゑ" survive only in highly specific, archaic contexts, such as in classical texts, certain historical names, stylistic artistic or poetic works, or in the deliberate evocation of an antiquated aesthetic, much like using "thee" and "thou" in modern English.

The primary implication of this distinction lies not in communication but in the domains of linguistics, historical study, and specialized literacy. For learners and modern readers, encountering "ゐ" or "ゑ" is a clear signal of pre-modern or deliberately archaizing text. Their presence immediately indicates that a document is either old, poetic, or attempting to convey a sense of historical authenticity. In linguistic terms, their existence is crucial for understanding sound changes in Japanese and for the accurate reading of literature from the Heian period onward. Furthermore, they remain relevant in the study of certain dialects or in the transliteration of foreign words from eras when the /wi/ and /we/ sounds were actively used in the kana system. For all practical purposes of writing and reading modern Japanese, however, the difference is absolute: "い" and "え" are the correct and only standard forms, while "ゐ" and "ゑ" are historical artifacts whose utility is now confined to scholarly and stylistic niches.