Like I said, I have to go back and read your article at FOTMD. I kind of see where your going with this and will work on wrapping my brain around it. Thanks. 

What i mean is that on a D whistle you would be playing the key of G in ionian mode (3 holes covered). On an A whistle you'd be playing the key of D in ionian mode.  
If you hear a lonesome/sad/spooky soundingtune, it's more likely to fall comfortably in either aeolian mode (one bottom hole uncovered) or Dorian mode (the 4 bottom holes uncovered).  That would mean on a D whistle you'd likely be able to play the sad tune most easily in Eminor or Aminor.  
Likewise the more cheerful tunes are typically in Ionian or Mixolydian modes...which fall on the whistle with the home note being all holes covered (D on a D whistle), or with bottom 3 holes uncovered (G on a D whistle).  Clear as mud i suppose.  ;D

But yes you can expand your capabilities a great deal by half-holing the whistle.  and- This translates directly to having extra half-frets like the 6.5 on the dulcimer!  

--
Site Owner

Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990

I'm terrible about modes even though you do a great job on FOTMD.

You can play D tunes with an A whistle. As well as G tunes with a D whistle. Is this what you mean? When you have a problem, you half hole the note. 

Wow Bill-  I love that!!!!  It's incredibly helpful for us folks coming to the whistle from being mountain dulcimer players.

I too had a revelation of sorts along this very same line as you did, but my brain applied it as the four main dulcimer modes and i'm using it to figure out where a tune's 'home' note might fall on the whistle, as follows:

I noticed that certain minor-sounding tunes on the whistle most often had their home note on two particular places/holes on the whistle, while the major sounding tunes most often centered on two other specific holes.  Then I realized it followed the very same position pattern as the fretboard on the diatonic dulcimer's 'home' location of the 4 common modes: mixolydian, aeolian, ionian, and dorian!  M ixolydian= all holes covered/open string(zero fret). Aeolian=1 hole uncovered/homenote on 1st fret.  Ionian= 3 holes uncovered/homenote on 3rd fret.  Dorian=4 holes uncovered/homenote on 4th fret.

I was thunderstruck by that when i realized it a couple months ago.  And your post makes it even clearer in my mind now.  
This all helps me find the right place on the whistle to start tunes from and be sure I have the right scale and the sharps and flats I need for the tune. Discovering that really let the light shine into my brain concerning the whistle and translating tunes back and forth between the whistle and stringed instruments.  So cool!

Like the black and whites note pattern on a piano, the dulcimer's diatonic fretboard with its pattern of mode-based scales can relate to the hole patterns on the penny whistle, and understanding one can help you with the other. 

--
Site Owner

Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990

As a mountain dulcimer player and pennywhistle player I had an aha moment early one morning (2am-ish) when I couldn't sleep. The melody line of DAD tab equates to the holes on a D whistle. Look at Boil Them Cabbage. 0 = no holes open. 1 = 1 hole open and so on. 7 = no holes open but blowing harder to reach the second octave d. I've taught at several festivals using this. It works! I don't have any formal music training. I'm an ear player. When you start looking at other songs you learn "tricks". Take Rosin The Beau. Starts on the middle string A note. Two choices....Play the second octave A or just skip it. It won't be missed if your playing with other instruments. Hope this gets your juices flowing. Enjoy the ride. 

updated by @billd: 01/30/20 01:32:23PM