Bob Dylan's influence on popular music is incalculable. As a songwriter, he pioneered several different schools of pop songwriting, from confessional singer/songwriter to winding, hallucinatory, stream-of-conscious narratives. As a vocalist, he broke down the notions that in order to perform, a singer had to have a conventionally good voice, thereby redefining the role of vocalist in popular music. As a musician, he sparked several genres of pop music, including electrified folk-rock and country-rock. And that just touches on the tip of his achievements. Dylan's force was evident during his height of popularity in the '60s — the Beatles' shift toward introspective songwriting in the mid-'60s never would have happened without him — but his influence echoed throughout several subsequent generations. Many of his songs became popular standards, and his best albums were undisputed classics of the rock & roll canon. Dylan's influence throughout folk music was equally powerful, and he marks a pivotal turning point in its 20th-century evolution, signifying when the genre moved away from traditional songs and toward personal songwriting. Even when his sales declined in the '80s and '90s, Dylan's presence was calculable.