The schwa symbol is used when transcribing a schwa sound for a word into the International Phonetic Alphabet. This character, which appears as an inverted and reversed "e," describes an unaccented and unstressed neutral vowel sound similar to "uh."
The first recorded use of the inverted "e" symbol for a schwa is generally attributed to an 1821 grammar book of Bavarian German by Johann Schmeller to describe what had been historically described as the murmur, natural or indeterminate vowel. It is linked to the Hebrew vowel diacritic "shva," used to indicate an "eh." Additionally, the first codified definition of the word schwa is attributed to the 1885 Oxford English dictionary, which describes the character and associated vowel sound.
As the most common vowel sound in English, the schwa has a history that dates back to dialects of the language spoken in the 11th to 15th century, generally referred to as Middle English. The Great Vowel Shift in the language, occurring coterminously with this period, increased the stress of certain vowels in the spoken language. The other, unstressed vowels of multisyllabic words homogenized to the sound referred to as a schwa contemptuously.
As the English language continuously evolves, syllables with a schwa vowel are more likely to disappear than a stressed vowel. Additionally, some dialects of the language insert the vowel sound, a phenomenon known as schwa epenthesis.