have trouble understanding the concept of "modal triads". Some people use terms like Lydian or Phrygian triads, but if you build tertian triads on a Lydian scale you end up with "standard" (major/minor/dim/aug) ones. If you use other triads, like quartal triads for example, you end up with different triads, but not 1-#4-5 (Lydian triad). Thank you.


The standard meaning of 'triad' is a set of three notes that can be stacked vertically in 3rds. 1,3,5 of some (7 note) scale.

So it's a bit of a misnomer to speak of the 'Lydian triad' (1-♯4-5) and the 'Phrygian triad' (1-♭2-5). But the terms are generally understood as describing the chords, built on the root of a Lydian or Phrygian scale, that may be seen as stating the essence of those modes. The 'tonic triads' of those modes if you like.

  • Would it make sense to describe them as trichords? Or are these triads literally being used as, say, sus#4 or sus#2 chords? – awe lotta Dec 25 '19 at 19:36
  • 'Trichord' has a specific meaning, These chords MIGHT fit it. Without context we don't have any way of knowing how they are being used. – Laurence Payne Dec 26 '19 at 1:30
  • According to en.wikipedia.org/wiki/Trichord, "In music theory, a trichord [...] is a group of three different pitch classes found within a larger group." What very specific meaning are you referring to? – awe lotta Dec 26 '19 at 22:54
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    You cut the Wikipedika definition short. "A trichord is a contiguous three-note set from a musical scale". The pitches under discussion are not contiguous within a normal scale. They might be within some other type of pitch set. – Laurence Payne Dec 26 '19 at 23:44

So we start of with understanding what I triad is. It's just a 3 note chord and the way we label these triads are with numbers and their relations to the scale degree (the major scale to be precise) for example a C major triad is 1 3 5 (CEG). I'm assuming you understand that so if not type a comment and I'll explain it in more detail.

So if we look a the "modal triads" what we are doing, is extracting the main flavours from the modes themselves and putting them into chord form.

Start with the Ionian Triad. well that's just 1 3 5 (a major triad)

Aeolian or minor triad is 1 b3 5 (pretty standard)

then lets look at a dorain triad. The dorian Mode is 1 2 b3 4 5 6 b7 8 so in the first 5 notes theres nothing different about it from the Minor scale. Meaning you still get a minor triad but you can add a 9th (2nd note) or the 11th (4th note) which you still get from an aeolian triad. Therefore we don't get dorian traids.

Phrygian is different, the scale is 1 b2 b3 4 5 b6 b7 8. So in this, we know we can get a minor triad but looking at it theres a b2. Meaning we can have a triad which is 1 b2 5. Which varys from the sus 2 triad from a minor or major scale being 125.

Lydian is the same but just as a major scale. Having the formula 1 2 3 #4 5 6 7 8. The #4 can be replaced from the 3 giving the lydian triad as 1 #4 5.

Mixolydian doesnt have one.

Locrian is is 1 b2 b3 4 b5 b6 b7 (you could have a feild day with this) therefore we have the diminished chord. Then you can insert a b2 giving 1 b2 b5 or a 4 giving 1 4 b5.

  • Why are you only using the first five notes of each scale to construct triads? – awe lotta Dec 26 '19 at 23:04
  • Also, why would you add a 9th or 11th? Wouldn't that no longer be a triad? And if you do use extensions, why not just use the 7th (i.e. for mixolydian -> dominant 7th chord) and even the 13th or 6th (i.e. for dorian -> minor add6)? – awe lotta Dec 26 '19 at 23:11
  • Well you need to write the first 5 notes of the scale to construct a triad but I was saying if you add the 9th or 11th (without the third) it doesn't construct a unique chord unlike adding the b9 – random10101010 Dec 27 '19 at 20:54
  • Why are you only using the first five notes? A triad is any three notes. Are you only including 1-3-5 chords and sus chords? – awe lotta Dec 27 '19 at 23:26
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    Everything is based of the root notes major scale. E.g. notes 6 8 3 would be A C E. being an A minor triad – random10101010 Jan 2 '20 at 4:39

FWIW, there is other terminology using primary or tonal chords/triads for the I, IV, and V chords and secondary or modal chords/triads for the ii, iii, and vi chords.

That isn't the meaning you ask about, but it seems worthwhile to mention it can mean something else in another context.

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