Forming the plural of a noun in English is pretty easy — mostly you add final -s to the singular form (with occasional spelling modifications:  story -> stories).  Linguists refer to nouns that form their plurals with final -s as count nouns.  Another group of nouns referred to as mass nouns generally don’t take final -s because what they refer to in the world is viewed not as countable items, but as an undifferentiated whole, e.g., starlight, fog, dirt, rice.  It’s easy to count three stories, four boxes, five dogs, but starlight, fog and dirt are not so easily countable. Of course specific contexts can override the ordinary mass noun interpretation; a chef might speak of different qualities of Asian rices, for example, or an ichthyologist might refer to fishes of the Indian Ocean. In such contexts, plural -s signals a comparison among kinds of an aggregate or substance.

There are also some curious English nouns which refer to countable items, but such nouns in the singular nevertheless take final plural -s.

• pants
• trousers
• shorts
• breeches
• culottes
• tights
• drawers, boxers (clothing sense only)

Breeches is a double plural, having added plural -s to what was already the plural brec for the Old English noun broc (a garment covering the thighs and loin).  Trousers comes from Gaelic triubhas (close-fitting shorts) and may have gained its r on the pattern of drawers.

The human body is symmetrical and it’s not surprising that body garments come in pairs. We have pairs of gloves, sleeves, stockings and shoes. But it’s also natural to speak of tearing or losing a single glove, sleeve, stocking or shoe. Yet no one refers to tearing a short, tight, or pant — the garment’s ‘pair plurality’ remains intact.

• he tore his pants/*?he tore his right pant
• a rip in her tights/*?a rip in her left tight

Evidently single garments which include covering for paired portions of our anatomy maintain a precarious semantic balance between being a single unit and a paired (plural) unit. This contrasts with gloves and socks, where a pair of gloves always means two separate items.

But it’s not so straightforward. Single coverings for the upper portion of the human body that include covering pairs of appendages (arms, hands) seem to be simple count nouns.

• shirt
• blouse
• coat

A pair of blouses means two separate garments whereas a pair of pants means a single garment. But then we have tails — an informal reference to the single upper garment tailcoat.  The phrase the tails he wore for the wedding were taken to the dry cleaners refers to a single garment, not two garments. Hmm. Could it be because tails is a part of the coat which covers lower anatomy, not upper anatomy?

The noun clothes is an interesting case; it has final plural -s, but refers to an aggregation, not a countable set of items. The expression he took his clothes off  implies that more than one piece was removed, but the word clothes resists numerical precision. (This is similar to the situation with mass nouns such as fog and rice.) Whereas you can easily say he removed three hats or he put on two gloves, it’s really odd to say he removed three clothes. Quantifiers which don’t enumerate the quantity are more natural: he removed some/all/few of his clothes.  Cloth was the singular form in Old English for clothes, but the meaning of cloth has shifted over time and no longer serves as the singular form of a garment. Did clothes become more of a mass noun as a consequence?

Other semantic domains exhibit ‘pair plurality’ to some extent, including tools with two matched appendages.

• scissors
• pliers
• shears

The above terms occur naturally with pair, as in pair of scissors, and they follow the lower-anatomy body garments in those cases by referring to a single item, not two items. SImilarly, it’s odd to speak of  a shear, a plier or a scissor.  These are more natural in the context of being a modifier, as in a scissor blade (similarly, a trouser seam).

Finally there is trou. The word was unknown to me, but a rower tells me that it refers to streamlined shorts worn by scullers. Given that, it certainly looks like a shortening of trousers. Is it a recent innovation? Does trou take final plural -s?  Can it occur with pair as in a new pair of trou?  Perhaps it’s more of an aggregate along the lines of clothes, where only context or quantifiers indicate how many items are referenced.  I would love examples if you have them!