Premise: Black Sabbath were an English rock band , formed in Birmingham in 1968 , by guitarist and main songwriter Tony Iommi , bassist and main lyricist Geezer Butler , singer Ozzy Osbourne , and drummer Bill Ward . The band experienced multiple line-up changes , with Iommi being the only constant member throughout its history . Originally formed as a blues rock band , the group soon adopted the Black Sabbath moniker and began incorporating occult themes with horror-inspired lyrics and tuned-down guitars .
Hypothesis: Black Sabbath is a band.
Label: ENTAILMENT