The origins of the Arabic alphabet can be traced to the writing of the semi-nomadic Nabataean tribes, who inhabited southern Syria and Jordan, Northern Arabia, and the Sinai Peninsula. Surviving stone inscriptions in the Nabataean script show strong similarities to the modern Arabic writing system. Like Arabic, their written texts consisted largely of consonants and long vowels, with variations on the same basic letter shapes used to represent a number of sounds.
Arabic is written and read from right to left. There is no distinction between upper- and lowercase letters, though shapes of letters usually vary depending on whether they are in an initial, medial, or final position in a word. Punctuation marks were not adopted until the twentieth century. Short vowels, represented by a set of marks below or above the letters, aid in the pronunciation of a word—these are usually only written in the Qur'an, where correct recitation is important, and in texts for novice readers.
The Arabic alphabet consists of eighteen shapes that express twenty-eight phonetic sounds with the help of diacritical marks. The same letter shape can form a "b" sound when one dot is placed below (ب), a "t" sound when two dots are placed above (ت), or a "th" sound when three dots are added above (ث). (See fig. 10 for more examples.)