Because Paul Simon excelled at writing such great melodies and, along with Art Garfunkel, sang some of the most gorgeous harmonies heard on the radio in the '60s, Simon & Garfunkel's achievements in sound architecture are often overlooked.

But listen closely to 1968's Bookends and 1970's Bridge Over Troubled Water, their last two albums, and you'll hear one of the most adventurous studio groups of the era – one that was every bit as sonically explorative as any of their more lauded contemporaries in this field.

The seeds were planted on their third album, Parsley, Sage, Rosemary and Thyme from 1966. That's especially true on the closing track, a juxtaposition between the "7 O'Clock" newscast, filled with sobering reports on Vietnam and civil rights, and the Christmas hymn "Silent Night." But Bookends, released on April 3, 1968, was something grander and more ambitious.

For starters, the duo was thinking in terms of albums rather than singles at this point. Up until then, they pretty much had made their name with a series of Top 40 singles (three of them, in fact, ended up on Bookends).

Listen to Simon & Garfunkel's 'Bookends'

So, their fourth LP was a concept album of sorts – partly inspired by the Beatles' Sgt. Pepper's Lonely Hearts Club Band and Simon's writing experiments on hashish – about the cycle of life told through a series of songs bookended, if you will, by two versions of "Bookends Theme": the album-opening instrumental that runs 30 seconds, and the side-closing take that includes vocals and is almost a minute longer.

The rest of the album is made up of a mix of songs the duo recorded that had no place within the first side's concept or were left over from The Graduate soundtrack, which was released less than three months earlier and made it to No. 1, the first Simon & Garfunkel-affiliated LP to do so. Plus, those three Top 25 singles that came out in the year leading up to were on there.

Together, they form a cornerstone record of the '60s, and a huge creative leap for Simon & Garfunkel, who found in Roy Halee and John Simon co-producers who helped shape much of the record's sound – from the string and brass arrangements heard in several songs and the sampled bit of "The Sound of Silence" hidden among a torrent of noise running throughout "Save the Life of My Child" to the widescreen sweep of "America" and "Fakin' It" and the array of layered instruments and sound effects that line the entire album.

Garfunkel even visited a retirement home and recorded old people talking about their lives and then edited it into the sound collage that leads into the closing tracks on Side One, while Simon ran himself and Garfunkel through dozens of vocal takes until he got just the one he wanted.

Listen to Simon & Garfunkel's 'Mrs. Robinson'

And then there's Simon's songwriting, which takes a more personal stance on songs like "Overs," "America" and "Mrs. Robinson." It all serves as a preface to Bridge Over Troubled Water's textured canvases (the percussive handclaps that launch and then propel "Fakin' It" are a precursor to the rhythmic stomp of "Cecilia") and more introspective lyrical themes. They were somewhat of a gamble here that paid off.

"Mrs. Robinson," buoyed by The Graduate's buzz and success, shot to No. 1, giving Simon & Garfunkel their second chart-topping single. Bookends featured the first album appearance of the song; it had only been included as two brief sketches on the hit Graduate soundtrack. That album was also home to "The Sound of Silence," which became the duo's first No. 1 in 1965 after electric instruments were added to the original acoustic version of the song.

Bookends also climbed to No. 1 and stayed there for seven weeks, pretty much supplanting The Graduate after a total of nine weeks in that position. But more than that, it elevated Simon & Garfunkel to a new level. Simon once referred to Bookends as "our first serious piece of work," and it stands decades later as the record that transported a perfectly pleasant folk act to a more consequential place.



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