When The Turtles entered the Billboard Top 40 on 21 August 1965 with a cover of It Ain't Me Babe that turned Bob Dylan's hip put-down into a cheery pop tune and then proceeded to go Top Ten with it, it confirmed a revolution that had been building throughout 1965: the marriage of two forms hitherto thought irreconcilable.
In 1963, folk was considered authentic, adult music, and rock largely fun for teenagers. Yet by 1965 the styles had merged to bring both folk and rock to a place that neither could have reached on its own.
Dozens of folkies subsequently scampered to go electric, even if it meant grafting electric guitar and drums onto a previously released acoustic track, as producer Tom Wilson did for Simon and Garfunkel's brooding The Sound Of Silence.
Most monumentally, Dylan himself went electric, first on record, then in concert, inciting howls of outrage from purists who wanted their folk music "uncontaminated".
Folk-rock's most important legacy, however, was introducing a newly sophisticated intelligence into rock music lyrics, whether in socially conscious songs, surrealistic landscapes or probes into the workings of the inner psyche.
Soon those traits would spread beyond folk-rock into all of rock music, dragging its audience into adulthood along the way.