"I'm not physically tired; I'm mentally tired in a way that I don't know how to explain exactly."

It shouldn't be that surprising. At 77, Simon has a strong claim to be America's greatest living songwriter, with an award-winning career spanning seven decades -- first as one half of Simon & Garfunkel, then as a genre-defying solo artist.

Art Garfunkel, left, with Paul Simon, around 1957. They were known at the time as "Tom and Jerry."

But now, Simon has decided to stop. It's not quite retirement, but it comes close. In September, his final tour concluded in Flushing Meadows Corona Park, near where he grew up in Queens, New York. But as he explained to Christiane Amanpour for her show on CNN International and PBS, this isn't a final goodbye.

'Good' songs, 'overlooked'

"I don't intend for it to be my last performance," he said at his office in New York -- just his last tour.

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"I'd like to do it for my own pleasure, in concert halls that have prestige sound and with perhaps different musicians that I admire, and play a repertoire that is different from what I've been playing."

It's a repertoire, he pointed out, that includes songs he's been playing for decades.

And what songs. With "Bridge Over Troubled Water," "Mrs. Robinson" and "Graceland," Simon has provided something of a soundtrack to the American experience.

With his most recent and possibly last album, "In the Blue Light," he has dusted off some of his back catalog, rearranging and revising some of his favorite songs.

"These are songs that I thought were well written -- good songs that were overlooked, or people didn't notice them when I put them out," he said.

Paul Simon performing in London, around 1980.

If this indeed proves to be his last album, Simon considers that very much his own choice.

"It's not like I couldn't do another album now at the same qualitative level as I've done the last two or three albums -- which I think are as good as I can do, as I've ever been. I think I could do that, but I'm not sure that's the most interesting choice for me."

Still, he acknowledges that even if he wants to let go of songwriting, songwriting may not let go of him: "I can't help but think music. It seems it's always there. I wake up with it."

At its best, songwriting for Simon comes close to a mystical experience. When he finished writing "Bridge over Troubled Water," he recalled, he had to admit to himself: "'That's better than I usually do.'"

Simon performing during the 2016 Democratic National Convention in Philadelphia.

"Graceland," he said, also fell into that category, "where you feel as if you are a conduit and the song is coming through you. You're shaping it, but you're absolutely surprised at what's happening, and you don't know why, and you don't know where it comes from.

"But I recognize that that happens sometimes, and it's led me to be a more spiritual person -- because of the mystery of it."

He has learned to accept that process for what it is.

"I'm holding back from going into solving these musical thoughts, as if they were puzzles that needed to be solved.

"Now I say, 'No, don't solve it that way. Just leave it alone. Let's just see what happens.' "

From 'Tom and Jerry' to Paul Simon

It was over half a century ago that he started performing with Art Garfunkel, originally under the stage name Tom & Jerry. It would become one of the most renowned musical pairings in history.

Simon and Garfunkel perform during a reunion concert at London's Wembley Stadium in 1982.

As a solo artist over the decades, Simon has continually reinvented himself, using music as a tool of global exploration: South Africa for "Graceland," Brazil for "The Rhythm of the Saints."

But he remains, at heart, a New Yorker. So much so that after 9/11, the city called on him numerous times to reflect New York's feelings in song; most memorably, Lorne Michaels asked Simon to open "Saturday Night Live" on September 29, 2001, the first episode of the show after the attacks.

The memory of that performance still moves him.

"What I remember most about that moment was coming from the dressing room to the studio, where my mind is -- as it usually is when I'm about to perform -- focused on what I am about to do.

"But I passed by these lines of firemen and policemen, and the reality of what had occurred and what the situation was. ... The context that I was performing in was very powerful. Very powerful. It took away from any sense that it was going to be a regular performance.

"It was very emotional. And it's seldom that I feel my heart pounding -- not really on any of those times in Central Park or in front of people. But that night, that night, and again on the 10th anniversary of 9/11 when I sang down at the World Trade Center in front of the families, that was also..." He trails off and shakes his head.

With these performances, Simon has had to acknowledge that he inhabits a healing role for the city.

"I've come to realize that I have that capacity, yeah. I'm surprised. I didn't plan it -- I've observed it."

Graceland

Simon hasn't always been a healing figure. In particular, the release of 1986's "Graceland" was surrounded by controversy. Simon traveled to South Africa to record with black musicians at a time when the country was still under the apartheid regime, and he was subsequently accused by some artists of breaking the cultural boycott against the country. At the time, he met his critics head on, and more than 30 years later, his opinion hasn't changed.

"They were completely disingenuous about it," he said. "First of all, we didn't break any boycott. There was no rule about recording with black South African musicians. In fact, the whole purpose of the boycott was the antithesis of what we did.

Simon with the South African musician Joseph Shabalala, founder of the group Ladysmith Black Mambazo, with whom Simon collaborated on "Graceland."

"The musicians voted whether they wanted me to come or not. I didn't know that, but I found out later on that they had voted. And what they wanted to know, the musicians, was, 'How much are we going to be paid? And will we get credit?' So that was easy, you know. Of course they were going to get credit and royalties. And I paid them, at that time, what was -- I think it was triple scale of what you would be paid in New York. So I think it came out to be like maybe $600 for a three-hour session. They were making like $15 for a day. So everybody was perfectly happy."

One of the groups Simon worked most closely with on the album was Ladysmith Black Mambazo, whose founder, Joseph Shabalala, embraced Simon both figuratively and literally -- the first time, he said, he had ever hugged a white man.

In the end, it's that message of unity that Simon hopes the album still carries: "It's very hard to get the trust, but musicians will often bring it on a level that goes right to the heart. It's really true that music is the universal language. It's a cliché, but it happens to be true."

Leaving a trail for environmentalists

When it comes to finally making peace with his most famous musical partner, Garfunkel, Simon demurs: "I don't know how to even approach that."

He mulls the question for a while.

"There's too much damage that was done. But, you know, it's like somebody that I've known since I'm 11, so I understand. I understand -- I think I understand why it happened, but I think it's best to stay away. Stay away just for safety's sake. And so I do."

Without a final reunion in the cards for this famous duo, and with Simon's touring career behind him, he is turning instead to more personal matters, including the cause that he cares about most: the environment.

Simon, right, with Art Garfunkel, around 1965.

During his penultimate tour, Simon gave the proceeds to the Half Earth Foundation, and in his final tour he donated money to a local charity or group in each city he played: "A small amount, $25,000, as a thank you."

"I was going and trying to leave it as like a trail of breadcrumbs through the forest so that people, if they were following it, would join."

In fact, while he generally seems at peace with his life and his choices, Simon admits he feels tremendous guilt about the environmental mess that he is leaving his children and grandchildren.

So, what of his musical legacy? It's an inheritance he's more reluctant to assess.

"I don't believe in legacy," he told Amanpour. "I don't believe that there's any importance to it.

"I've already left a great deal of my thinking. I just turned 77, so I've already left my thinking through these songs -- some of which are very, very well-known -- so it's good to stop and see what else will I think of. Or maybe I won't. Maybe I'll just take a rest."