DEAR MISS MANNERS: My mother taught me that one has shoulders covered for dinner when the occasion is formal (or even "festive," in the new locution). Shoulders may be bared after dinner, if there's dancing. Still the case?
GENTLE READER: Lest anyone suspect your mother's sound counsel of being based on prudery, Miss Manners points out that no mention was made of bosoms. As long as the shoulders are covered, much of the bosom need not be, a situation of which Victorian ladies took startling advantage.
The distinction is between a dinner dress and a ball dress. A strapless dress worn at dinner gives the effect, to the opposite side of the table, of a naked lady sitting in a bathtub. More importantly, a dinner dress does not have a billowing skirt likely to encroach on the gravy-spilling area allotted to the gentlemen on either side. Ball dresses may lack sleeves and add the extra material to the skirt.
While it is true that dinners sometimes include dancing, and balls sometimes feature midnight suppers, Miss Manners expects ladies to follow the rules for the primary events they attend. If they solve the problem by stripping half way through the evening, she promises to look the other way.