Debatably, Black Sabbath laid the groundwork for various subgenres of metal with individual songs from their early catalog, exploring cosmic psychedelia on one track, symphonic accompaniment on the next, and sludgy, downtuned riffing on the song after that. If the theory that Sabbath forecast a great deal of metal to come, Vol. 4 represents the earliest ancestry of doom metal as one of the band's darkest and most confused early documents. The three albums that came before 1972's Vol. 4 weren't short on dread and doominess, but the band's increasingly heavy mutations of blues-rock were kept from the brink of collapse by relatively streamlined production and aspirations for pop accessibility.