Referring to small letters (a, b, c) as opposed to capital letters, used in typography and writing.
From printing terminology where small letters were kept in the lower case or drawer, while capital letters were in the upper case. Term dates to the 1680s in English printing.
The physical arrangement of type in printing cases gave us this spatial metaphor that perfectly captures hierarchy - even today, we speak of uppercase letters as 'big' and lowercase as 'small,' preserving the printer's workshop in our language.
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