We probably say "a pair of pants" and not "a pair of shirts" because  
the pants are made up _mostly_ of the two legs, while shirts or  
sweaters have a substantial amount of surface devoted to covering  
other large body areas, like the upper trunk of the body. "Pair of  
underpants" may just be modeled on "pair of pants", since "pants"  
occurs in both, and underpants are a kind of pants.

"Pant" and "trouser" as singulars are part of fashion terminology and  
indicate a higher level of expertise in fashion and clothing than the  
everyday "pants" (or so the Nordstrom clerks would have us believe).  
The word in the singular refers more to the _style_ of the item,  
rather than the individual pair of pants; it refers to a stylistic  
category or "model" of pants rather an individual pair. Hence the  
number differentiation may have nothing to do with number, but more  
to do with categorization and social indication of expertise. Perhaps  
focusing on the style of the pant emphasizes the unity of its  
features. It seems to me (just an impression; not based on data) that  
it would be very odd to say "which pant are you wearing to give your  
lecture", but not odd to say "we have a very nice new pant from Donna  
Karan." In fact, the former version makes me think of it as a  
question of which _style_ of pants the person is going to wear.

This question points to the importance of what cognitive linguists  
call "construal" -- the way we foreground and background different  
characteristics of a scene or object. "Pair of scissors" foregrounds  
the object's two-part nature; same with "glasses" and "pants" or  
"trousers". "Pant" or "trouser" foregrounds the uniqueness of the  
style, especially as differentiated from other styles.

Numerous words are differentiated solely by foregrounding different  
aspects of scene: "above" and "below" refer to the same concrete  
scenario, but foreground different relations within it; "hot" and  
"cold" are opposite points on a single scale. The fact that British  
English treats "couple" and "government" as grammatically plural  
while American English treats them as singular is accounted for in  
cognitive linguistics by saying that the British version focuses on  
the fact that the group contains more than one person; the American  
version focuses on the fact that the group forms a cohesive entity.

Someone else may  have expertise on "six pair" and similar  
constructions. Obviously, plural marking is redundant in these cases,  
and languages often allow dropping of redundant markers (this is a  
regular feature of African American English, for example).

Dr. Johanna Rubba, Ph. D.
Associate Professor, Linguistics
Linguistics Minor Advisor
English Dept.
Cal Poly State University San Luis Obispo
San Luis Obispo, CA 93407
Ofc. tel. : 805-756-2184
Dept. tel.: 805-756-2596
Dept. fax: 805-756-6374
E-mail: [log in to unmask]
URL: cla.calpoly.edu/~jrubba

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