What is a tetragraph?
A tetragraph is a sequence of four letters that together form a single sound. In native English words, these only occur when GH is used in conjunction with various vowel pairs to form specific vowel sounds: AIGH, AUGH, EIGH, and OUGH. For the first three of these, it could be argued that they are not really tetragraphs—that GH is simply silent following vowel digraphs—but we’ll examine them here for the sake of completeness. First, let’s look at the combination that can be called a true tetragraph.
The sequence OUGH is quite common, but it is also one of the trickiest to learn because it can result in six different sounds. In two of these, GH makes the sound /f/, so it is functioning as a digraph paired with the vowel digraph OU, which can make either the /ɔ/ (as in cot) or /ʌ/ (as in up) sounds:
- cough (/kɔf/)
- enough (/ɪˈnʌf/)
- rough (/rʌf/)
- slough (/slʌf/)
- tough (/tʌf/)
- trough (/trɔf/)
When OUGH is functioning like a true tetragraph (forming a single vowel sound), it can be pronounced /oʊ/ (as in go), /u/ (as in too), /ɔ/ (as in got), or /aʊ/ (as in cow). The sounds created are unique to its spelling (that is, not all of them could not be formed from the digraph OU alone).
Let’s look at some examples of each:
plough (usually spelled plow)
(*In British English, borough and thorough are pronounced /ˈbʌrə/ and /ˈθʌrə/, respectively.)
(**Slough takes this pronunciation when it means “a depression or hole filled with mud,” “a swamp, marsh, or bog,” or “a degraded or despairing condition.” When slough means “an outer layer or covering” or “to discard an outer layer,” it is pronounced /slʌf/.)
There are three other combinations of letters that could be considered tetragraphs in English. In these, the GH is usually simply silent—its presence doesn’t dictate a pronunciation that is unique from the vowel digraph it follows. However, there are a couple of exceptions.
This combination is pronounced /eɪ/ (the “long A” sound) and only appears in the word straight or words derived from it (straightaway, straighten, straighter, etc.).
Like AIGH, this combination is also usually pronounced /eɪ/. For example:
- eight (/eɪt/)
- freight (/freɪt/)
- inveigh (/ɪnˈveɪ/)
- neigh (/neɪ/)
- neighbor (/ˈneɪbər/)
- sleigh (/sleɪ/)
- weigh (/weɪ/)
However, there are two words in which EIGH it is pronounced /aɪ/ (the “long I” sound): height (/haɪt/ and sleight (/slaɪt/). (This pronunciation also carries over to words derived from these two, such as heighten or sleighted.)
There are two words in which GH produces the sound /f/ in this combination: laugh (/læf/) and draught (/dræft/ or /drɑft/), which is the British English spelling for draft.
Otherwise, AUGH will always produce the sound /ɔ/ and will always be followed by the letter T:
- aught (/ɔt/)
- caught (/cɔt/)
- daughter (/ˈdɔtər/)
- distraught (/dɪˈstrɔt/)
- fraught (/frɔt/)
- naught (/nɔt/)
- onslaught (/ˈɔnˌslɔt/)
- slaughter (/ˈslɔtər/)
- taught (/tɔt/)
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