There are but a handful of musical artists of the last half-century who have had the impact of David Crosby. He came to prominence as a founding member of the Byrds, the Los Angeles ensemble that, in the mid-1960s, pioneered, among other genres, folk rock and acid rock. Later in the decade, the singer-songwriter teamed with Stephen Stills and Graham Nash (and, sometimes, Neil Young) to create some of the Woodstock era's most beloved and enduring music.

In the 1980s, Crosby, who is to perform Friday at Glenside's Keswick Theatre, made headlines for entirely different reasons - as a hard-drug abuser (freebasing cocaine appeared to be his favorite pastime) and for a series of drug- and gun-possession busts, the most serious of which happened in Dallas, for which he received an eight-year sentence on cocaine and firearms counts. He was paroled after only five months.

In 1994, he underwent a liver transplant.

Despite his sometimes-turbulent personal life, Crosby has continued to write, record, and perform in concert his folk-based songs, often in collaboration with others. On his recently released album, Lighthouse, he was joined by bassist Michael League (who produced the disc) and two vocalists, Becca Young and Michelle Willis, all of whom are out on tour with him (and all of whom are significantly younger than he).

During a recent phone call, Crosby was typically forthcoming about a variety of subjects, from the new album to Donald Trump to why he'll likely never reunite with his two still-living Byrds cofounders, Chris Hillman and Roger McGuinn. But he steadfastly refused to talk at all about the rift with Nash, his best friend of almost five decades.

What does Lighthouse say about who and where David Crosby is at this stage of his life?

It says I'm a very happy guy, because that's when I write like this. I've been writing a lot and writing with partners, [which is] something most people don't do, but I like doing it. It kind of doubles and triples the possibilities, and I like that.

It says that for some reason - and I have no explanation for it - I can still sing and play, which is kind of amazing. But it mostly says I'm happy. That's the bottom line. That's when I make good art.

That's interesting because so many "artistes" will tell you great art comes from great suffering.

Us artists have been trying to sell that story for a long time, and I think it's a load of crap. I think it's just an excuse for having our lives in complete disarray. I'm familiar with it, actually.

You think? But it sounds like you are, indeed, in a much better place than you were in other times of your life.

Oh, man, so much better.

It's interesting that your current collaborators are all very much younger than you are.

I didn't pick it that way, but, yeah. I like people who feel the same as I do about music: It's our life. It's not something we're doing to get laid, or get rich, or to get famous. It's our life. We don't really have a choice about it. It's a calling or something. I'm not exactly sure how to describe it right, but I know they are like me. Music is what we do. We do our family and our music, and that's pretty much it.

I've spent time doing other things during my life - sailing and diving - but my whole joy is in creating music. That's what I was supposed to do, I'm convinced of that. And since my family is good . . . then the music is pretty much the deal, and [League, Young, and Willis] are like that. Yes, it's great they're younger than me; they have great energy. But they've all been doing it for a long time, they're all leaders of their own bands, and they've been doing it their whole lives.

Has the actual act of composing songs changed for you over the last 50-plus years, or are you still writing from the same exact place you always did?

Yeah. I write mostly about love. I find people absolutely fascinating, so I write about people and how they see the world. Occasionally, I'll see something that I think I got to point out, and I'll go back to the "troubadour" part of our history as songwriters, and I'll be the town crier and say, 'Hey, it's 12:30, and you just elected an idiot.' You know, that kind of thing.

How different is what the 75-year-old David Crosby has to say from that which his 25- or 35-year-old counterpart had to say?

A great deal. There are some drastically huge lessons that I had to learn, like don't waste time. When you're 25 or 30, you think you have all the time in the world. When you're 75, you think every minute is totally precious and a pearl beyond price and not to be wasted. I wish I had known it when I was 25.

What were your expectations when you first turned pro? Did you ever fantasize, much less expect, you'd have such an important and influential career?

I don't know, I might have fantasized it, but I don't remember. I had no idea how it was going to go. I just knew I loved playing music and just had to do it. So, whatever happened was going to happen. I didn't know it would turn out like this. But I'm glad it has. It's been a wild ride.

Did you ever envision you'd still be doing it in 2016?

Not when I was in the middle of being a druggie. I didn't envision that I'd live much longer. But I did, and when I got past that, I felt incredibly lucky that . . . I had another shot at it. So I tried to take it as seriously as I could.

You were among the earliest pop stars to use your position as a political soapbox. I imagine you have a thought or two to share about the president-elect.

I think he's a disaster, and I think he'll probably prove that himself. I think there are a lot of things that are really, really sad about that situation. One, the electoral college. Hillary Clinton won [the popular vote]. There isn't any question she won. It should be the popular vote [that determines who wins a presidential election].

I don't particularly like Hillary Clinton. I just think he's a whole lot worse. I was a Bernie [Sanders] supporter. I still am. I think he's a decent guy. I thought he would have made a great president.

You and Chris Hillman have long made known your desire to reunite with your fellow founding member of the Byrds, Roger McGuinn, but, apparently, it's never going to happen. What's the story behind that?

Chris [Hillman] and I would love to do it - it's good music, and it was a great band. Roger [McGuinn] really likes being on his own, and he does not want to do it. And I have to respect that. You know, I own the name, and I could put a band together and go out as the Byrds. But Roger was the main man of the Byrds, and I couldn't do it without him. If he doesn't want to do it, it's not going to happen. That's pretty much it. It's his decision, and I have to respect it.

But it sounds like you're disappointed.

Sure, I'd love to do it. I'd love to do it.

"An Evening With David Crosby & Friends," 8 p.m. Friday at the Keswick Theatre, 291 N. Keswick Ave., Glenside. $45-$68, http://www.keswicktheatre.com.