Excess has two faces. The linguistic connection between "presumptuous" and "sumptuous" is closer than their contrasting manners suggest: both descend from a Latin verb meaning "to take," though one concerns claiming too much authority while the other concerns spending enough to make abundance visible. Their shared ancestry is not a coincidence of spelling.
Presumption takes liberties first. Through prefixation, the ancestral verb acquired the sense of taking beforehand, which could mean anticipating something or accepting it before sufficient grounds had been established. The family includes "presume," "presumption," and "presumptuous," whose accusatory force concerns unwarranted confidence or conduct beyond accepted limits. Permission becomes the issue. A presumptuous request does not merely ask for something; it acts as though the right to ask, expect, or interfere has already been granted. The offense lies less in taking an object than in taking a liberty that another person has not offered.
Luxury takes another route. The same Latin verb produced a noun for expense or expenditure, from which an adjective meaning costly or extravagant developed before reaching English as "sumptuous." Spending supplies the bridge. What was taken up or used became an outlay, and an adjective associated with heavy expenditure came to describe rich furnishings, elaborate meals, and magnificent surroundings. This is semantic divergence, not contradiction: related words can inherit different senses from intervening forms rather than preserve one unchanged definition. The resemblance still bites. At a sumptuous table, abundance invites admiration; a presumptuous guest assumes the best seat is already theirs.
