There were no lower case letters at first, and K, Y and Z used only for writing words of Greek origin. The letters J, U and W were added to the alphabet at a later stage to write languages other than Latin. J is a variant of I, U is a variant of V, and W was introduced as a 'double-v' to make a distinction between the sounds we know as 'v' and 'w' which was unnecessary in Latin. @Curionic

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