An alphabet is a standard set of letters (basic written symbols or graphemes) which is used to write one or more languages based on the general principle that the letters represent phonemes (basic significant sounds) of the spoken language. This is in contrast to other types of writing systems, such as syllabaries (in which each character represents a syllable) and logographies (in which each character represents a word, morpheme, or semantic unit). The Phoenician script was the first phonemic script and was the ancestor of modern alphabets, including Arabic, Greek, Latin, Cyrillic and Hebrew. According to a terminology introduced by Peter T. Daniels, an “alphabet” in the narrow sense is one that represents both vowels and consonants as letters equally. The first “true alphabet” in this sense was the Greek alphabet, which was developed on the basis of the earlier Phoenician alphabet. In other alphabetic scripts, such as the original Phoenician, Hebrew or Arabic, letters predominantly or exclusively represent only consonants; such a script is also called an abjad. A third type, called abugida or alphasyllabary, is one where vowels are shown by diacritics or modifications of consonantal base letters, as in Devanagari and other South Asian scripts. There are dozens of alphabets in use today, the most popular being the Latin alphabet (which was derived from the Greek). Many languages use modified forms of the Latin alphabet, with additional letters formed using diacritical marks. While most alphabets have letters composed of lines (linear writing), there are also exceptions such as the alphabets used in Braille, fingerspelling, and Morse code. Alphabets are usually associated with a standard ordering of their letters. This makes them useful for purposes of collation, specifically by allowing words to be sorted in alphabetical order. It also means that their letters can be used as an alternative method of “numbering” ordered items, in such contexts as numbered lists.