Semitic languages like Arabic and Hebrew base the formation of their words on a system of root letters and patterns. Thus, most Arabic words have a root (or stem or origin) that consists of three letters, mostly consonants but some vowels count too. Some words have four root letters. The root expresses a general meaning and most words with the same combination of root letters are related. This system is extremely productive for word building and predicting the gist of the word. Understanding the concept of root and pattern enables students to grasp the general meaning of the word and often translate it even without the help of a dictionary. Estimates of the number of different root combinations which exist vary between 5,000 and 6,500.