Why do we say “A pair of Underpants” (pants, knickers, briefs, whatever you like to call them)
They are only one item so why do we use the term ‘pair of’?
And why ‘a pair of trousers’ and not ‘a pair of shirts’. We say ‘a pair of trousers and a shirt’ :dubious:
I am sure you can figure out what I am getting at at this point.
Well, back in the day, pants really were a pair . You wore two leg pieces, laced to a loinpiece in the center. Thus, a pair of pants. 
url=http://www.straightdope.com/classics/a2_249b.html]The Master speaks.
The Elephant Shrew screws up his coding.
(Darn Quick Reply with no preview…)
Warning: the following is a WAG. It has not been certified by the FDA, the Library of Congress, or the American Kennel Club. As such the reader will be advised law that the side effects from the following WAG have not undergone rigorous clinical studies, may be factually incorrect (as was the spelling of the previous word), and has not been certified by the AKC. (as it is a WILD ass guess, rather than a purebred ass guess)
Way back when, in the times before underoos, men used to wear something known as a “codpiece”. These men were fishermen who stuffed their catch down their front garments to impress the ladies. The codpiece was rather small so as to confine the cod to the proper area. This left the legs bare. The fishermen used something called a “stocking” to protect each leg while they were fishing for larger, firmer cod. Naturally, these garments were called a “pair” of stockings.
Eventually, the women folk in these pre masengill times tired of their husbands’ scents being more fishlike than their own, and the fishermen were forced to cease the practice of cod stuffing. To prevent further cod stuffing, and to make laundy day less toilsome, the womenfolk sewed the “pair” of stockings on to the codpiece. Though it was originally three garments, the legs were considered the important pieces. This is understandable after generations of ichtyological-penile contact. This new garment was first called a “pair” of stockings, but later a “pair” of pants (Pant was derived from how the women folk breathed after realizing that their man didn’t have a five day old fish in his crotch)
After much chafing to his boys, the fisherman devised a garment modeled after his “pair” of pants, which would prevent further irritation. This was naturally called “underpants”. As the garment stemmed from stockings, and men have two legs (well, most anyway) it is now refered to as a “pair” of underpants.
Damn, I’m so juvenille. The funny thing is, some of the above is probably true
And on the other side of the same coin, why is a “bra” singular?