Sum and substance
The top becomes the bottom. "Sum" means
the total of an addition, and has spawned figurative meanings: we "sum
up" or "summarize" anything, we extract the "sum and substance" of a complex
topic. "Sum" derives from L. summa, meaning the topmost line, reflecting
the Roman practice of adding a column of numbers up and casting the result
in the top line. (We still "add up," for some reason.) Our practice is
to add down and cast the result in a line below the column of figures which
gives us "the bottom line." Hence the top has become the bottom.
"Substance," incidentally, is from
sub-, under and stare, to stand. Sub-, in turn is
*upo, which meant under but also gave rise to "up from under"
meanings, including "up" itself. So down has become up. And when we grasp
the "sum and substance" of something, we know it "from top to bottom."
"Top" is from a Gc root, with no
visible IE antecedent, but some(1) think
that "bottom" derives from IE *bhudh-, which also gives us "fundamental"
and "profound" via L. fundus.
1. Claiborne. Not in AHD.