You probably knew that we'd be doing something like speaking with Paddy Moloney here during the Green Beer season. But there's a twist: We're talking with the Chieftains' leader, arguably the prime mover of the modern Irish music world for 40 years now, about Scottish music.

What's the difference? Well, unless you're putting cable-knit Irish pub balladeers against be-kilted Highland pipers, it may not be that great.

"It's only 14 miles of a difference there across the top of Ireland to Scotland," the loquacious uilleann piper, who'll turn 70 in August, says. "There has to be this connection."

The two Celtic regions share a lot of tunes, he notes, and certainly a lot of instrumentation, particularly fiddles. But while he says he can generally tell one from another, he's hard-pressed to articulate exactly how someone not quite as expert in it as he is might identify the essential characteristics that mark one from the other. And he's been spending a lot of time thinking about it lately. The Chieftains are currently on a U.S. tour specifically bringing Irish and Scottish music together, the trek set to conclude at Carnegie Hall on St. You-Know-Who's Day.

He can hear it in his head but more as a continuity of stylistic idiosyncrasies flowing not just one island to another but within each as well. "If you take the fiddle, for instance, and go up the West Coast of Ireland from Kerry to Country Clare, there's a different way of playing, of bowing," he notes. "And then up to Donegal and you get closer to the way of Scotland, and then move over to Scotland, just their own approach to the same tune with decorations and improvisations. You hear the same tune, but it sounds different to the uneducated ear because of how they do it, from their traditions. It's like playing the music of Brittany on our album 'Celtic Wedding,' the Chieftains' versions of Bretons playing the same tunes we know. Each place has its own approach. For me it's like a dialect. Think of Canadian and American ways of speaking English, or go from Dublin down to County Cork, which is just 160 miles away, and it's very hard to understand what they're saying."

He slips into Cork-speak for a few phrases to illustrate, and then seems to notice that he hasn't actually done the same in terms of the music. "Ah! Forgot that I was going to explain it," he says, bursting into a mischievous laugh.

But explain it he can't, at least not in so many words -- not that he ever seems to run short in that department. Instead, we suggest that maybe he can just suggest some Scottish music that has inspired him, that could be held up next to highlights from the Chieftains' extensive catalog of Irish material, so fans can make some assessments of their own. And off we go on a Source-Outing run:

• "Years ago, there was a band called Jimmy Shand and His Accordion Band," he says, referring to an act popular in the British Isles for a long stretch of the mid-20th century (and honored in song by folk-rocker Richard Thompson with the wry 1991 polka 'Don't Sit On My Jimmy Shands'). "And Jimmy Shand made many Scottish albums. Used to listen to them as a child, they played them on the radio."


• "There was Billy Connolly as a ballad singer -- he and I got plastered one night at London airport. The fog canceled our flights. He was going to Scotland and I to Ireland. He was a folk singer in those days, before he was a comedian and actor. And Edinburgh was a second home to us, Maggie May's pub. The gatherings there!"


• "I remember in 1968 playing at the Edinburgh Folk Festival with a group called the Corries. They were huge in those days. We went and stayed with them. It was so close, just like going to another part of Ireland. They had many records. As does the Battlefield Band."


• "The Boys of the Lough, their flute player Cathal McConnell: I remember playing at the Edinburgh Festival once, myself, him and the fiddle player from that group. We did a set together, did some Scottish tunes and songs, and then they joined in with the Chieftains. A really good comparison would be a Boys of the Lough album and the Chieftains album 'The Water From the Well' we did a few years ago. We did a tour of Ireland, went to different places to get different styles, musicians from County Clare like Tommy Peoples, who comes from Donegal but plays in Clare. That particular album is a good one to judge. We went to Donegal and played with the group Altan, and they have a style of fiddling that's close to Scotland there. " 'Water From the Well' has a lot of Irish styles from the West and South and from around Dublin, and the track with Altan gets close to Scotland, and then you hit the Boys of the Lough by continuing to go that way. You will notice the difference."
  

And that brings us back to the current tour, for which the Chieftains recruited some Scottish musicians and even dancers to come along for this latest exploration of the Celtic connections.

"We've gone further this time, with a Scottish singer Alyth McCormack, a traditional singer from Lewis, a little island off the western coast of Scotland, with the very pure style for which Scottish traditions are known."

It's a lively bunch on the tour, the four core members (Moloney, flute player Matt Molloy, singer/bodhran player Kevin Conneff and fiddler Sean Keane) all part of the band since the '70s, joined by various young associates, including harpist Triona Marshall, whose fluid facility on the plucked stings helps fill the void left by the 2002 passing of longtime member Derek Bell, though she likely can't match the bespectacled Belfast imp's wicked and often wittily vulgar humor.

But arguably this program brings them closer to home than many (and certainly the highest-profile) projects the group has done in the last 15 years or so. That time has been marked by star-filled concept works such as 1995's 'The Long Black Veil' album, which featured Van Morrison and the Rolling Stones, 1999's 'Tears of Stone,' with female guests including Bonnie Raitt, Sinead O'Connor and Joni Mitchell, and the pair 'Down the Old Plank Road' and 'Further Down the Old Plank Road,' which brought Dublin and Nashville together with Vince Gill, Alison Krauss and Rosanne Cash among the guests.

Bell's death certainly put some focus back on the group's root achievements, and the 2006 'Live From Dublin' album tribute to their departed comrade concentrated on traditional Irish material played in the true Chieftains way -- alternately lyrical and heels-up sprightly. Moloney has also been looking back at the origins and history of his band courtesy the BBC, which has done a documentary on the group, set to air this month, though he's not particularly comfortable with the summing-up exercise of the BBC film. "I get nervous when they start doing the in-depth documentary," he confesses.

Instead, he'll look ahead. There's a project in discussion with Ry Cooder, a tour of Japan after the U.S. jaunt, likely some film soundtrack projects (he played on the score of the Loch Ness-ian fantasy 'The Water Horse' recently, the latest of many film music sessions) -- a tightly packed schedule that he refers to as "trying to trim down a bit." It's a pace he's kept up for more than 40 years. You'd hardly expect him to slow much now.

"Once a Chieftain," he says, "always a Chieftain."