A brief guide to modes in Celtic, English, and American tunes
By Jonathan Lay, September 28, 2020. Updated September 14, 2021.

You’ll hear it in the mysterious, strong, tangy, rich, or haunting sounds of bagpipe tunes, mountain ballads, and old fiddle tunes. Melodies that don’t quite turn in the direction you thought they would. Harmonies that are powerful but not quite expected. Music that is not in a major or minor key, but something else. Familiar but different. Another mode.

If you are a musician playing tunes from Celtic, English, or North American roots, you may be perplexed by the notion of tunes having “modes” besides major and minor keys. You might hear that a tune is in a “Dorian,” “Mixolydian,” or “Modal” key, but not be quite sure what that means. This brief guide to musical modes applies to Irish / Celtic, English, and North American tunes. I’ll just refer to them as Celtic tunes for the sake of brevity. (Be aware that there is a rich palette of Blues and pentatonic scales, and scales that come from non-Western cultures, that this guide won’t discuss.) 

Overview

Here’s a preview of some of the key points that we’ll get into in more detail.

• The four modes generally used in Celtic and North American tunes are:
  • Major (Ionian)
  • Minor (Aeolian)
  • Dorian
  • Mixolydian
• A key signature doesn’t fully indicate the key a tune is in. For example, a tune with a C Major key signature might be in C Major, A Minor, D Dorian, or G Mixolydian.
• Major (Ionian) and Mixolydian modes resolve to a major chord.
• Minor (Aeolian) and Dorian modes resolve to a minor chord.

Major, Minor, and WTF?

Most of us, as we begin to play tunes, get a pretty good understanding of major and minor keys. Then we may start seeing tunes with scales and keys that are neither major nor minor. You can think of these as “Weird Tune Flavors,” or WTF, for short. Or call them “Wonderful Tune Flavors” if you prefer. Either way, WTF. Scales and keys, whether major, minor, or WTF, are associated with “modes.”

Modes?

In the lingo of Western music theory, the word “mode” is used instead of “flavor” to refer to these WTF scales and keys. For tunes that have their roots in the Celtic lands and England, you are going to run into just two WTF modes: Dorian and Mixolydian. You might run into special WTF names for major and minor keys: Ionian mode is the same as major; Aeolian mode is the same as minor. And you’ll run into people describing the key of a tune as “modal” or “Mountain Modal” — these terms just mean that the mode of the tune is vaguely in the WTF category.

What do they Sound Like?

• Major (Ionian) — that’s the “normal” mode for tunes. It tends to sound “happy” or emotionally neutral.
• Minor (Aeolian) — tends to sound sad, mysterious, or haunting.
• Dorian — sounds like a minor key, but with a twist. The “twist” sounds slightly exotic to people who grew up with American pop music, but pretty normal to people who grew up with bagpipe, banjo, and tin whistle music.
• Mixolydian — sounds like a major key, but with that twist.

Seven Modes

There are a total of seven modes that are core to Western music theory. As I said, you will probably only use four of these for Celtic and North American tunes: Ionian (major); Aeolian (minor); Dorian, and Mixolydian. But it is helpful to understand that there are seven modes. Not by coincidence, seven is also the number of note names for the white keys (A, B, C, D, E, F, G) on a piano keyboard. Diatonic instruments, like tin whistles, also play scales with seven named notes (that’s before you start bending notes sharp or flat, of course). These are the names of the seven modes:

Seven Piano White Keys

A good way to understand modes is to think of just the white keys on the piano keyboard. The musical scale that begins on the C piano key, and is played just on the white keys is the C major scale. It is made up of the notes C, D, E, F, G, A, B. There is a mode name that goes with major scales: Ionian.

The first note or degree of the C major scale is C (that’s the scale’s “tonic”). But what if you start the scale on a different note? What if instead of starting at C, the first degree of the C major scale, you start on D? The scale that starts on D and is played on the piano white keys is a different mode: it’s the Dorian mode. 

If you were to start the scale on the next note, E, the scale would be in yet a different mode: Phrygian. For each of the seven named white keys on the piano, the scale starting there has a different sound and a different mode name. The sound of each of these scales is different because the pattern of pitch intervals between the notes is different. The table below illustrates how you can play each of the seven modes by starting on a different piano white key.

What about our good old major and minor keys? Those have mode names that only get used when you are speaking of music theory: Ionian mode is the same as a major key; Aeolian mode is the same as a minor key.

Seven Modes on a Piano’s White Keys

Starts on C Major Scale Degree	Mode Name	Scale Name	Notes in Scale
1	Ionian	C Major (C Ionian)	C-D-E-F-G-A-B
2	Dorian	D Dorian	D-E-F-G-A-B-C
3	Phrygian	E Phrygian	E-F-G-A-B-C-D
4	Lydian	F Lydian	F-G-A-B-C-D-E
5	Mixolydian	G Mixolydian	G-A-B-C-D-E-F
6	Aeolian	A Minor (A Aeolian)	A-B-C-D-E-F-G
7	Locrian	B Locrian	B-C-D-E-F-G-A

How to Find the Tonic Note of a Tune

The tonic note of a tune is where the tune is “at home.” Sometimes it’s easy to identify what the tune’s tonic note is: if the key signature is C Major, and the tune resolves to an A note and an A minor chord at the end, then the tune is probably in A minor. Or if the key signature is D major, and the tune resolves to an E note and an E minor chord at the end, then the tune is probably in E Dorian. It’s often not that straightforward though. Sometimes tunes don’t end on their tonic note, and sometimes the A part of the tune is in a different key or mode than the B part. There are other features of tunes that can make it tricky to identify with certainty what mode they are in, and there are other “tricks” for identifying the mode. Getting into those tricks is a topic that won’t fit into this short guide.

Key Signatures and Modes

The key signature of a musical score doesn’t fully tell you what key the tune is in. What the key signature does is identify the “relative major” of all of the modes that match that key signature. If the key signature of a tune is C Major (no sharps or flats), then the tune might be in C Major, D Dorian, G Mixolydian, or A minor. For each of those keys and modes, C Major is the relative major key.

If the Tonic note of the tune is this degree of the key signature’s relative major	Then the tune’s mode is	Examples
1	Major (Ionian)	If the key signature is C Major and the tune’s tonic is C (the first degree of the C Major scale), then the tune is in C Major. If the key signature is G Major and the tune’s tonic is G (the first degree of the G Major scale), then the tune is in G Major.
2	Dorian	If the key signature is C Major and the tune’s tonic is D (the 2nd degree of the C Major scale), then the tune is in D Dorian. If the key signature is G Major and the tune’s tonic is A (the 2nd degree of the G Major scale), then the tune is in A Dorian.
5	Mixolydian	If the key signature is C Major and the tune’s tonic is G (the 5th degree of the C Major scale), then the tune is in G Mixolydian. If the key signature is G Major and the tune’s tonic is D (the 5th degree of the G Major scale), then the tune is in D Mixolydian.
6	Minor (Aeolian)	If the key signature is C Major and the tune’s tonic is A (the 6th degree of the C Major scale), then the tune is in A Minor. If the key signature is G Major and the tune’s tonic is E (the 6th degree of the G Major scale), then the tune is in E Minor.

Tune Endings (You say you want a resolution?)

When tunes come to an end, they typically end on their tonic note, and on their tonic chord. For C major, the tonic note is C, and the tonic chord (the “one” chord, or tonic triad) is C Major. Another way of saying this, is that the tunes resolve to the tonic and the harmony resolves to the tonic chord. The tonic chord, or tonic triad, is made up of scale degrees 1, 3, and 5. That’s C, E, and G in the C Major scale. In D Dorian, the tonic triad is a minor chord composed of D, F, and A. One thing that makes modes sound different from one another is the kind of chord they resolve to:

• Major and Mixolydian resolve to a major chord
• Minor and Dorian resolve to a minor chord

Why Are Celtic Tunes in Those Four Modes?

Celtic tunes are in Major, Dorian, Mixolydian, and Minor keys. Why those four? Here’s my theory: if you are playing a diatonic instrument like a pennywhistle or bagpipe, those four modes come built-in. So, let’s say you have a D pennywhistle or a bagpipe with a chanter in D. If you are not bending any notes, a tune with a tonic note of D will have a D Major (Ionian mode) scale on the instrument. If the tune has a tonic note of E, the scale the instrument gives you is E Dorian. If the tune has a tonic note of A, the scale the instrument gives you is A Mixolydian. And if the tune has a tonic note of B, the instrument gives you a scale of B minor (Aeolian mode). Since those four modes are built into these essential Celtic instruments, it makes sense that Celtic tunes would be in those modes. The same effect would hold for music played on any other diatonic instruments.

Chords and Harmonies in Modes

We’ve already looked at resolving to the tonic (“one”) chord in Ionian, Dorian, Mixolydian, and Aeolian modes. Beyond the “one” chord, the interval relationships in other chords (like the “four” chord or the “five” chord) are different for different modes. This makes harmonies and chord progressions sound distinctly different for each mode. 

The table below shows the type of chords for each scale position in four modes. A common chord progression for tunes is I-IV-V. For a tune in C major, those chords would be C-F-G. In any major key, the I, IV, and V chords are all major. So, the I-IV-V chord progression in the Ionian (major) mode is major-major-major. That’s not the case in the other modes: In Dorian mode, the I-IV-V chord progression is minor-major-minor; In Mixolydian mode it is major-major-minor; In Aeolian (minor) mode it is minor-minor-minor. In a similar way, other chord progressions will have a distinctly different sound among the modes.

Wrapping it Up 

Modes might seem mysterious, but I hope you’ve seen that they are really pretty easy to understand. If this brief guide has made you curious for more about modes, use it as a starting point and dig deeper. A web search on “music theory modes” will bring up a bunch of links to videos, illustrations, articles, and audio samples. If you are just playing tunes, and wondering why one is referred to as “Dorian” and another as “Minor” I hope gives you a working understanding of modes.