One Pair, Two Pair, Red Pair, Blue Pairs

I held up the pairs of glasses and said "I've got two pair here."

"Two pairs, " I was immediately corrected.

"No," I insisted, "pair is on of those nouns that keeps the same form when it  becomes plural." Although I had never really thought about my instinct to say "pair" instead of "pairs" even when plural. So off to the internet I went via my trusty Blackberry.

It turns out that I'm not the only one wondering about this. From The Grammar Logs:

QUESTION
We are wondering at our school what is the correct plural form for "pair"?

There is a question on an end of level test for third grade that poses this question: I bought two new ______ of stockings. The students must choose between pair, paires, pair's and pairs. The teacher's in our school are split between pair, and pairs.

Please help us so we can teach our students the correct word. Thank you!

GRAMMAR'S RESPONSE
That's a ridiculously tough question for third graders. It is possible to use the word pair as the plural of pair: "We've sold several pair of stockings this morning," but I think you'll find most dictionaries preferring pairs: "We've sold several pairs of stockings this morning." I think "pair" as the plural of pair is more of a regional or dialect usage.

Merriam-Webster online simply says "plural pairs or pair." My copy of Webster's Unabridged is more specific: "pl pairs, sometimes after a number, pair."

But even before looking it up, it occurred to me that I would only use "pair" as plural after a number. This makes sense, if it's a bit inconsistent. The number before "pair" removes any ambiguity over whether you mean one or more. But "the red pair" doesn't make clear whether you mean the two pair that happen to be red or just one red pair.

I'm not sure where I picked up using "pair" as plural after a number. I fully admit that "pairs" appears to be preferred and is more consistent. But I'm not changing. So there.

A pair of related questions:

Why do we say a pair of pants (or glasses) when there is only one item involved?

First of all, let's note there is a class of objects that are thought to consist of two independent but connected parts, usually identical or at least similar to each other. In addition to pants and trousers, there are eyeglasses, scissors, tweezers, shears, pliers, and so on.

The terms for these objects are always plural in form, and they are usually referred to as "a pair of ...." This usage goes back to at least 1297 AD, when we have the expression "a peire of hosen."

The implication is that the two parts are separable in some sense, and in fact a pair of hose can often mean two separate pieces. (True, you can't separate tweezers, but I never claimed the English language was rational.)

In contrast to trousers, a shirt is thought of mainly as a covering for the torso, and may or may not have sleeves. Hence no pair.

The "pair of ..." designation is somewhat arbitrarily applied. At one time it was common to speak of a pair of compasses (for drawing), a pair of nutcrackers, or a pair of bellows. But I would venture to say that in the U.S., at least, these expressions are dying out.

On the other hand, we do speak of a pair of panties, even though panties aren't really a pair of anything, having (usually) no legs. But clearly this is merely an extension of the expression, "pair of pants."

Is "pair" itself singular or plural? That is, is it "the pair of glasses is on the shelf" or "the pair of glasses are on the shelf", even when you clearly only mean one pair? The answer is, it depends.

The noun pair can be followed by a singular or plural verb. The singular is always used when pair denotes the set taken as a single entity: This pair of shoes is on sale. A plural verb is used when the members are considered as individuals: The pair are working more harmoniously now. After a number other than one, pair itself can be either singular or plural, but the plural is now more common: She bought six pairs (or pair) of stockings.