The usual way these languages developed was through the addition of Hebrew words, phrases, and sometimes grammar used to express uniquely Jewish concepts and concerns. Often they were written in Hebrew letters, including the block letters used in Hebrew today and Rashi script. Due to the insular (isolated) nature of many Jewish communities, many Jewish languages retained archaic (old) vocabulary and linguistic structures of the language from which they descended long after they had been lost or changed in later forms of the parent language.