Comments by "EebstertheGreat" (@EebstertheGreat) on "A guide to our alphabet" video.
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Your explanation for the use of K in Latin is wrong. It wasn't used before different vowels than C, but for a different sound. In early Latin, C was used for all /k/ and /g/ sounds and S was used for all /s/ sounds. Thus you have words like "cuius" and "calendae." Later, Q was used before U in some words like "qui," for reasons I haven't been able to track down. Note that in Greek, qoph was used interchangeably with kappa when it was used at all (which was rarely). K was used in a small handful of Greek loanwords, and there inconsistently, e.g. in "kalendae" sometimes, but not before certain vowels, just sort of at random. K didn't become common in Latin until the third or fourth century. The C sound had shifted by this point from /k/ to /s/, explaining why some words that had a kappa in Greek have an /s/ sound in English, like "Cyprus." But after this sound shift, Latin continued to borrow words from Greek, and these newer borrowings were spelled with a K to clarify the pronunciation. This explains why so many English words with a K that don't come from German derive from Greek. And for instance, compare Latin Hercules to Greek Herakles from which it derives.
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