Why do some words end in double consonants?
Why do we have double consonant letters? This is, for the most part, because originally in English and probably at one stage in French, there was a distinction between short and long consonants. For example, in early Middle English sune ‘son’ was distinct from sunne ‘sun’. When the following consonant was long or doubled, the vowel sound before it was—or became—short, and quite often when the consonant was short or single, the vowel sound before it was—or became—long. When the distinction between long and short consonants ended, during Middle English, the writing of a double, as opposed to a single, consonant became a useful device to show that the preceding vowel was short, and we still retain this convention (albeit inconsistently). For example: bitter versus biter, chaffer versus chafer, etc.
In the case of “s” there is a further complication: between vowels, the single or short “s” became the voiced sound /z/, whereas the double or long “s” remained /s/. Sometimes the /z/ was respelt as the letter “z”, but English seems rather resistant to this, and “z” is used in spelling far less that it is sounded.
Additionally, the plural ending, spelt –s, which had originally had the sound /s/, came in early modern English to be pronounced /z/. This meant that you could now have /s/ or /z/ between vowels and also at the end of a word where a final “e” became silent and in the plural, and this could follow either a short vowel or a long vowel. Hence a system emerged whereby “ss” was used after a short vowel even in final position to show the sound of /s/, while final –s, or –se, stood for /z/ after a long vowel (rise, raise, ease, knees, keys). To show final /s/ after a long vowel, –ce was very often used, even in words that have no etymological relation to French or Latin, where this construction derives; so alongside piece, price, vice, etc., from French, we have twice, fleece, etc. (There is great inconsistency here as well, since we also have lease, cease, etc., and freeze, breeze, etc.).
Since there are three other consonants that have to be doubled when final after a short vowel, there may be other factors in the use of final double “s”. Whereas several consonants are single at the end of a word whether a long or a short vowel precedes (pod, food, rum, room, tin, seen, dip, deep, pot, pout), the letters “f”, “k”, “l”, in addition to “s” are single after a long vowel (or digraph such as “ea”) but double after a short one (‘deaf, leaf, puff, seek, neck, [with “kk” becoming “ck”]; heel, hill).
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