Another question from a Fight for English reader:
'On your discussion of the hyphen: I came across a modern American non-fiction book (sadly, I can't now locate it) where the diaeresis was regularly used, instead of the hyphen, for "coöperate" and the like. I don't know whether this was a given publisher's house style, an author's preference, or even how widespread this usage is. It would be fun to know how this came about, and how much it is used on each side of the Atlantic. I rather like its arcane nature, whilst also find it intrusive!'
Marks to distinguish letters and words, as an aid to reading, go back to classical times. The term diaeresis (earlier diæresis, US dieresis) derives from a Greek word meaning 'divide' or 'separate'. In English the practice goes back to the end of the 16th century, when most of the modern punctuation marks started to be systematically used. The earliest reference to the term in the OED is 1611, where it is used to distinguish adjacent vowels in such words as queuë - the intention being to ensure that the vowel sequence was not pronounced as a diphthong.
These days, the vowel-separating function seems to have largely died out, being replaced by the hyphen. I still see it occasionally as a pronunciation guide in such words as naïve. And it's still quite often found in proper names, such as Noël or the Brontës. Some people are quite proud of it. I know a woman who, when asked her name, says 'It's Chloë with two dots'.
I don't know of any statistical study of contemporary usage, I'm afraid, or whether different things are happening between the US and UK. Certainly, if any modern book used it frequently, it would have to be an authorial decision, bucking the trend, and there for a stylistic purpose. I've seen it, for instance, in representations of dialect speech and also in some artificial languages (as in science fiction), where it helps make the speech look alien. Nice subject for a small study.