Today, ‘gh’ is pronounced as /f/ as in ‘laugh’, /g/ as in ‘ghost’ or is not pronounced at all as in ‘plough’ or ‘night’.
It is interesting to look at the history surrounding this combination of letters as in fact there used to be far more words spelled with ‘gh’. In Shakespearian texts, for example, you can find ‘spight’ for ‘spite, ‘willough’ for ‘willow’ and ‘yaughan’ for ‘yawn’ and, in Middle English, ‘dwarf’ was spelled ‘dwargh’.
In the 1300s, the ‘gh’ letter combination was used to represent the way the ‘ch’ in ‘loch’ is pronounced by the Scots or in ‘Bach’ by the Germans. In that era, words like ‘right’ and ‘night’ were pronounced with this guttural sound. However, given the difficulty of this pronunciation, it is not surpring that gradually over time the pronunciation of these words gradually changed, eliminating this guttural sound (although apparently it can still be heard in some Scottish dialects).
Samples of writing from the between the 15th and 17th century show that many words which today are spelled with an unpronounced ‘gh’ indicate that these words used to be spoken with a /f/. For example, daughter was /dofter/ and plough was /plouf/.
The pronunciation of ‘gh’ as /g/ can be traced to William Caxton a printer who published over 100 manuscripts between 1476 and 1491. Many of the spelling decisions made by Caxton made English spelling more, rather than less, regular. This was particularly true of ‘gh’. Caxton had learned his trade in Germany and his assistants spoke Flemish (which is Germanic in origin). Apparently, ‘ghost’ was first spelled with a ‘gh’ in a book printed by William in 1484 and it is suggested that it was spelled with the extra ‘h’ because in Flemish it was written ‘gheest’. By the end of the 16th century everyone was writing ‘ghost’ and not ‘gost’. Slowly, the ‘h’ spread to other words appearing in ‘aghast’ and ‘ghastly’ in the 15th century. The ‘gh’ pronounced /g/ is also apparent in words borrowed from other languages, for example ‘ghetto’ and ‘spaghetti’ from Italian. In actual fact, we are lucky that there are so few words spelled with ‘gh’ and pronounced /g/ as in some books published by Caxton you can find ‘ghoos’ for ‘goose’, ‘ghoot’ for ‘goat’ and ‘gherle’ for girl.
Even though English may at times appear chaotic, it is still overwhelmingly regular. So, in terms of ‘gh’, it is only pronounced as /g/ at the beginning of words and syllables and it is either unpronounced or pronounced as /f/ at the end of words and syllables. Therefore, ‘ghoti’ could not be pronounced as ‘fish’!
Crystal, D. (2012). Spell it Out: The Singular Story of English Spelling. Profile Books: London.