The Hebrew alphabet has 22 letters. It does not have case. Five letters have different forms when used at the end of a word. Hebrew is written from right to left. Originally, the alphabet was an abjad consisting only of consonants, but is now considered an "impure abjad". As with other abjads, such as the Arabic alphabet, during its centuries-long use scribes devised means of indicating vowel sounds by separate vowel points, known in Hebrew as "niqqud." In both biblical and rabbinic Hebrew, the letters Yodh Waw (letter) He (letter) Aleph can also function as "matres lectionis", which is when certain consonants are used to indicate vowels. There is a trend in Modern Hebrew towards the use of "matres lectionis" to indicate vowels that have traditionally gone unwritten, a practice known as "full spelling".