Cross-rhythmic feel & a natural minor mode.
As the heyday of 90s alternative rock faded into the new & highly sound compressed century, many folks put the blame squarely on one person: Britney, b*tch. I'm not kidding. Rock stars said this as their album sales dwindled and their bands broke up. Cultural savants believed she was one of four musical horseman (Christina Augilera, Jessica Simpson, and maybe Mandy Moore were the others?) ushering in a musical apocalypse.
At the time, federal legislation was changing, and broadcasting would become further deregulated, allowing fewer & larger companies to shape the tastes of media consumers. But blaming Viacom & Clear Channel didn't make for unit-shifting journalism -- blaming Britney did.
Nearly 20 years into the modern pop-pocalypse, it looks like we're all still standing. Industry de-regulation and media consolidation has not necessarily been great for our democracy, but there's more music than ever out in the world to consume, most of it at the tips of our fingers. Many musicians & journalists are even starting to embrace our pop overlords, with even David Byrne giving implicit approval to Selena Gomez. Jamming to a Britney song doesn't lessen one's artistic integrity, and it didn't in 1999 either.
Intro: Having performed since her childhood years, Grammy winner Britney Spears became the face of the modern pop movement upon the release of her debut album ...Baby One More Time in 1999. She was the best selling Nielsen SoundScan female artist of the 2000s and has sold over 100 million albums to date. Released in the second act of her career, “Til the World Ends” was the second single from Spears’s 2011 album Femme Fatale. It was written by Kesha, Swedish juggernauts Max Martin & Alexander Kronlund, and Lukasz Gottwald. The song reached #3 on the Billboard Hot 100 Singles chart, reaching #1 in Poland and South Korea. Femme Fatale reached #1 on the Billboard 200 Albums chart, contributing to her almost 100 million records sold worldwide. "Till the World Ends" has also been featured as the closing number in Britney's Vegas residency show.
Analysis: Appearing in the pre-chorus section and repeated throughout the song, a measure emulating 9/8 occurs at :39 in the video recording linked above. In published versions of the song, the rhythm is expressed in 4/4 time, through syncopated dotted sixteenth notes. The note groupings, however, especially on the "whoa-oh-oh" sections give a strong impression of 9/8. The "whoa-oh-oh" theme is layered over the chorus later on in the song, giving the strong impression of cross-rhythms, although this theme could be interpreted as stress shifts, as well.
More information on stress shifts opposed to cross-rhythms can be found here.
Additionally, although only containing three chords, "Till the World Ends" can be analyzed in Aeolian mode. Published in c minor, the vocal melody starts on a C and almost always returns to a C at the end of phrases or major sectons. The chords are c-Eb-Ab, which would be i-III-VI in this particular key. Although there are no chromatic notes that reinforce the minor sensibility, the consistent departure & return to C are indicative of true Aeolian (or natural minor) mode.
Considerations for Teaching: Like many of Spears songs, strong sexually suggestive overtones are present here. While Spears is literally discussing dancing at a club, she includes a line in the second verse: “get you off with a touch dancing in the dark.” The pre-chorus and “woah-oh” sections can be played to exhibit the cross-rhythm concept without playing any part of the song featuring inappropriate content.