Although commonly referred to as the "Thai alphabet", the character set is in fact not a true alphabetbut an abugida, a writing system in which each consonant may invoke an inherent vowel sound. In the case of the Thai script this is an implied 'a' or 'o'. Consonants are written horizontally from left to right, with vowels arranged above, below, to the left, or to the right of the corresponding consonant, or in a combination of positions.