A reader writes:

Could Johnson possibly comment on the near-universal American use of "guys" to refer to mixed or even exclusively female groups. Is this done elsewhere? Is it new? Am I right in thinking it is the only noun in English whose gender depends on whether it is singular or plural?

The Oxford English Dictionary is not as helpful as usual here. It gives the relevant sense as "A man, fellow. orig. U.S.", and offers a slew of citations, the earliest being from 1847:

Swell's Night Guide, 41: I can't tonight, for I am going to be seduced by a rich old Guy.

But it doesn't go into the fact that in modern American English, "guys" in the plural can be directed at a mixed-sex or even an all-female group. "Guys" is spreading to British English too.

"Guys" wasn't always so adaptable. 1950 saw the opening of a Broadway show called Guys and Dolls. In this era it would have still been quite weird to refer to a group of girls as "guys". My suspicion is that with the rise of feminism came the idea that guys and, well, girls (I'll get to that in a moment) could all be "guys", that social groups should, in solidarity, see their commonality, not the differences. I also know people of both sexes who speak to a woman with the vocative "dude", so that word has trod the same path.

On a related note, I've just begun watching the newish HBO show "Girls". Those unfamiliar may think it is about children; in fact, it's about women in their mid-20s living in New York. Its creator, Lena Dunham, is female. But some young adult women consider being called "girls" condescending. "An adult female is a 'woman'," goes the tart retort.

But Miss Dunham's show wouldn't work if it were called "Women". The reason is that Ms Dunham's "Girls" is meant to be the feminine form not of "boys", but of our friend "guys". Yes, we have "girls and boys" (children), but we also have "girls and guys" (usually teens or young adults). A 22-year-old American female who's just met the male of her dreams will probably gush to her roommate "I've just met the most amazing guy!" And an American male in the opposite position would say "I've just met the most amazing girl!". The "girl and guy" pair here connote youth (on the part of the referent), but also informality (on the part of the speaker). Using the informal "girl" for a young woman in a place that calls for formality is when you get into trouble. Someone discussing a new hire would be ill-advised to say "Our choice has come down to this guy Steve and this girl Michelle."

We began with the point that "guys" can refer to a group of girls. But Ms Dunham couldn't have called her show "Guys". "Guys" works as a vocative to an all-girl group: "Let's go, guys!" But it doesn't work as a noun referring to them: "The guys are coming over". (Perhaps some people use "guys" this way for women, but I don't think I've heard it.) So "guys" has a funny distribution, and our correspondent might be right that no other word is used quite like it.