Hi, Megan—

I hate to disagree with Captain Birdseye (a sterling fellow indeed), but there really isn't any such thing as a "modal chord." What he is describing is what are called "open fifths."

In medieval times, modes were just regarded as different scales, and it wasn't until around the sixteenth century or so that the Ionian and Aeolian modes ("modern" major and natural minor scales) emerged as being somewhat more versatile than the rest, and the other scales fell into general disuse among mainstream composers. In medieval church music (Gregorian chants and such) music was generally monophonic (everybody singing the same melody) or polyphonic (two or more melodies interweaving, or sometimes the lower voices singing on just one note, a sort of drone). Oftentimes only the melody was written out and the singers or musicians were expected to improvise the rest of it. The intervals they used most were perfect, fourths, fifths, or octaves. Thirds, sixths, and other intervals (especially seconds and sevenths) were considered dissonant or "discordant." But times changed. It wasn't until around the sixteen century that chords began to emerge as such, and music developed a distinctly harmonic structure as well as a polyphonic one.

The problem with using only perfect fourths, fifths, and octaves is that they merely ride the strongest overtones of the fundamental notes and, as my music theory prof said, "they create no actual harmony." "Parallel" fourths, fifths, and octaves were a no-no in music theory exercises. It takes adding a third to the mix to give a chord (notes which sound "in accord," which is where the word came from) definition, identify it as major or minor, generally give it color, and create such things as "leading tones." Someplace along the line (a few centuries back) it was established that a chord consisted of a root (the note upon which the chord is built), an interval of a third above that, and an interval of a fifth also above the root. Like so for a C chord:    C D E F G — 1 2 3 4 5. Then you can "double" the notes—stack up as many Cs Es and Gs as you want, and it's still a C chord. The three notes that are needed to make a complete chord are referred to as a "triad." [You make 6th, 7th, 9th, and 11th chords by adding these intervals about the root to the triad;   but don't worry about that now. Jazz musicians use them a lot, but folk musicians rarely do.]

"Chords" composed of only perfect fourths, fifths, and octaves are often used by rock musicians, who usually refer to them as "power chords." They do come in handy for certain effects sometimes, but they're sort of like spices in cooking. They need to be used judiciously and sparingly.

Although there have been heated arguments about this on Mudcat threads, musicians, composers, and musicologists in the Western European tradition (to which we belong) are adamant that it takes three different notes to define a chord. Any two distinct notes (root and fifth, for example) are called an "interval." Sorry, but that's by definition.

So where does all this take us? Getting to the nitty-gritty of which chords to use when accompanying songs with modal melodies, it's nowhere near as complicated as people try to make it. No more complicated than working out chords for songs in scales we're more used to. Nothing really mysterious about it.

For a song in a major scale (which is Ionian mode, remember), the chords used to accompany it are derived from the scale itself. Let's use a C scale to keep it simple. This is a good rundown of how to build chords (or figure out chords) for any key:   Twang!   This is an excellent web sit, by the way. Lots of good information here.

Okay, let's take a song like "John Riley" that Joan Baez recorded, and say we want to do it in A minor. The chords available to us in A minor are Am, B diminished (which we don't really want to use), C, Dm, Em, F, and G. Sometimes the key of A minor might use an E or E7, which contains a note not in the scale (G#), but that's another issue, and we won't deal with that here. But when we get a few measures into the song, we find that the Dm and F chords are going to clank badly because the note being sung at that point is an F#. In fact, every time we sing an F, it's not an F, it's an F#! So we take all the notes in the song and spread them out at a scale sequence. And we discover that the scale is A B C D E F# G A. Not a regular minor scale. In fact, it's Dorian mode!

Okay, what to do about chords? To accommodate that F#, you can't use a Dm chord (which contains an F as the 3rd) or an F major—obviously! But now, the chords you have available for use, built on the Dorian scale, are:    Am, Bm, C, D major, E, F# diminished (which you don't want to use), and G.

Those are the chords that Joan Baez chooses from to accompany "John Riley." She may capo up, but as I recall, these are the chord configurations she uses.

Likewise, her recording of "The Great Silkie." It's almost exactly the same as a regular major scale. Let's assume the key of D:   D, E, F#, G, A, B, and C#. But we notice that there is no C# in the song if we do it in D. But there is a C natural. What looks like a major scale, but has a flatted seventh, is Mixolydian mode. The chords available are D, Em, F#m, G, Am, Bm, and C (no A major or A7, both of which contain a C#). The shift between the D and the C gives it a very modal sound. These are the chords that Joan Baez selects from.

She knows what she's doing.

Other than the regular major and minor scales, the Dorian and the Mixolydian modes are probably the ones you will encounter the most in British and American folk music.

Here's a pretty good run-down on modes:    Plonk!

I hope I haven't hopelessly confused the issue. Happy pickin'!!

Don Firth