Like any philosophy, political ideology, or school of thought, feminism isn't really a single, stable concept but more refers to a spectrum of ideas and beliefs about the role gender and sex play in human life and if they even exist in the first place.
If we were to further describe this spectrum but (for some reason) were allowed to speak only in terms of music from the 1960s forward, we might establish twin poles anchored by North American girl power appropriators the Spice Girls on one end and quintessential riot grrl progenitors Bikini Kill on the other.
Somewhere in between Baby Spice's hypersexed doublespeak and Kathleen Hannah's poetry about armpit hair -- just left of the Dixie Chicks, with a soulful smidgen of the South (verses the Chicks' Texan 'tude) -- lie the Indigo Girls.
While not quite Ani DiFranco, Amy Ray and Emily Saliers have always leaned a little more to the left than other early-'90s coffee-shop staples like Suzanne Vega and 10,000 Maniacs. They did, of course, spend some time on the legendary Lillith Fair, AKA Lesbian Lollapalooza.
However, so did Sarah McLachlan. And nobody is conflating building a mystery with burning a brassiere.
So the Girls aren't exactly preachy. But the lack of talking does nothing but amplify their walking. Ray and Saliers, as the Indigo Girls and in their private lives, have supported a number of progressive causes of the years, including the environment, the National Coalition to Stop the Death Penalty, and gay rights.
Even if your message is not 100 percent cause-oriented, actions have been known to speak louder than slogans.