In Old English the sounds (k) and (ch) were both represented by the letter c. Later, under the influence of French spelling, Middle English scribes inserted an h after c to indicate the (ch) sound at the beginning of words, as in child. (The sequence tch became the usual way to represent this sound following short vowels, as in catch.) In English words of Greek origin the digraph ch represents a transliteration of Greek X (chi), and so is usually pronounced (k), as in chorus, architect. And in English words borrowed from French, ch is often pronounced (sh), as in charlatan, cachet.
