The first complication is syllables that consist of just a vowel (V). This issue does not arise in some languages because every syllable starts with a consonant. This is common in Semitic languages and in languages of mainland SE Asia; for such languages this issue need not arise. For some languages, a zero consonant letter is used as though every syllable began with a consonant. For other languages, each vowel has a separate letter that is used for each syllable consisting of just the vowel. These letters are known as "independent vowels", and are found in most Indic scripts. These letters may be quite different from the corresponding diacritics, which by contrast are known as "dependent vowels". As a result of the spread of writing systems, independent vowels may be used to represent syllables beginning with a glottal stop, even for non-initial syllables.