- Historically in writing, many accents come from letters written above or below, or there was an existing use of the same letter for distinct sounds, so it was

- Historically in writing, many accents come from letters written above or below, or there was an existing use of the same letter for distinct sounds, so it was natural to mark existing letters rather than create new ones out of whole cloth. - The use of digraphs is frequently due to historical sound changes; first, certain sound combinations changed valence, but others do not. Then one rewrites with the digraphs with the other instances by analogy. Sometimes it comes from borrowing; for example the historical use of "ch" to denote the historic greek "chi", or aspirated chi sound, as in "chronograph" - Finally, it is easier to modify a existing type, or arrange movable type, to include an accent rather than to create one from scratch.