<font face="Verdana, Arial" size="2">A listener asked why it is we use the word pair when we talk about such things as "a pair of pants" and "a pair of reading glasses." Her point is an interesting one: since we don't usually talk about a single "pant" or only one "reading glass," why do we find it necessary to use the word pair?
For our answer, we peel away the many layers of meaning of the simple pair. Although it might be easy to assume pair has only one, fairly straightforward meaning synonymous with couple or twosome, in fact, the noun is used to name a number of things. Pair refers to two similar or associated things, such as two mated animals (a pair of horses), and it refers to a couple of humans in love (they were a devoted pair). Pair refers to two separate things that are identical or similar (a pair of twins), and it refers to two separate things that happen to be associated but are neither identical nor similar (the horse and rider made a fine pair).
Pair refers to a set of two corresponding bodily parts or members (a pair of eyes), and it refers to two corresponding things designed for use together (a pair of shoes). The term's final (although not its most recent) sense is the one that got us started today: pair refers to something made up of two corresponding pieces joined together at some point: a pair of pants, a pair of scissors, a pair of glasses.
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