In hand writing, a ligature is made by joining two or more characters in an atypical fashion by merging their parts, or by writing one above or inside the other. In printing, a ligature is a group of characters that is typeset as a unit, so the characters do not have to be joined. For example, in some cases the fi ligature prints the letters f and i with a greater separation than when they are typeset as separate letters. When printing with movable type was invented around 1450, typefaces included many ligatures and additional letters, as they were based on handwriting. Ligatures made printing with movable type easier because one block would replace frequent combinations of letters and also allowed more complex and interesting character designs which would otherwise collide with one another.