In every language people use letters to represent sounds, so, when you have two sounds and they converge in one, it’s possible one of those letters is also lost.
In the 14th century, in Spain, there were 6 sibilant (“s”-like) sounds, but they changed until the 3 of today (one s, one sound like “th” and one which is a hard “h”, used for “jamón” for example). The ç was used until around 16th century, but, when those 6 sounds converged into 3, it was not needed anymore, since the “s” sound is represented with “s”, the “th” with z or c (depends on context) and the “hard h” is usually j or g. So, there is no need for the ç anymore.
Latest Answers