I recently asked some of my female students, including 23-30+ year old grad students, why they referred to themselves and their friends as girls instead of women. I feared that their answer would involve the explanation that they didn't consider themselves feminists, but no, they just shrugged and said that the words "woman" and "women" sounded "old" to them. Their mothers are women, they are girls.
I told them that my college and grad school friends were quite insistent on being called women and not girls, in part because the male students were referred to as Men, and it was annoying to be considered a girl when our peers were considered Men. My students said they didn't think of their male peers as men, just as guys, dudes, boys, whatever. My most talented, independent, smart, energetic female students call themselves girls, and I know they see themselves as the equal (or better) than their male peers, so the girl/woman thing clearly doesn't have the baggage that it used to.
My generation drew the line at age 18 or so, but now I wonder where the boundary is for my grad students -- when they get their degrees? get married? get a job? have children? get some wrinkles? Or never? My aged aunt still refers to herself and her friends as "the girls", as did my grandmother. Perhaps there were a few decades in the late 20th century when "woman" was considered a positive term that was worth insisting on, but now that's over.
Even if the women/girl terminology is no longer an issue for some, I still correct my senior male colleagues when they refer to the women grad students (or undergrads, for that matter) as "girls", "gals", or even "ladies", since they do not refer to the male students as boys or guys or gentlemen. And I can't help it.
9 months ago