Many fans of jam music are intrigued by the improvisational techniques used by the bands they listen to. Those without a musical background may or may not have heard of the musical modes, however, simply put a mode is a scale. Most people have heard someone voice the syllables "Doh, re, mi, fa, sol, la, ti", which is essentially the seven notes of the major scale. The major scale is simply a mode. Without going into too much detail, scales and modes are a particular selection of notes within a particular key or octave. Modes act as a guide, letting the musician know which notes to play, and which notes to avoid in order to attain their desired sound. 
The ancient Greeks believed that music had the ability to evoke moods and behaviors. The Greeks defined these moods into seven musical scales, known as echos. The Romans later adopted the system renaming it modus. It was felt that each mode evoked a different emotion. Major modes were said to evoke happy, lively moods, whereas minor modes communicated feelings of sadness or seriousness. Plato recommended that soldiers going to battle avoid listening to music in certain modes as it would interfere with their bloodlust. Similarly, Plato and Artistotle both felt that a persons affinity toward a particular musical mode was an insight into that person's character.Modal jamming is largely felt to have originated with the release of Miles
Davis' "Kind of Blue." This album features Miles Davis and John Coltrane using the modes as a framework for their jams. Modal jams typically involve less changes in key, allowing the musician to solo more fluidly. John Coltrane (who plays sax on the album) would go on to explore modal jamming to an all new level and is considered one of the great modal interpreters. For an example of this early modal jamming, check out this clip of Miles Davis' So What, which is also covered by Jerry Garcia and David Grisman on their album "So What":Let's now take a look at each of the seven modes, how they are used in jam music, and what types of moods they evoke. Without any further ado, I present to you:
The Musical Modes
1. Ionian - The Ionian mode is the major scale. It evokes bright, happy feelings. It should also sound more familiar than some of the other modes. Here are two examples of how the Ionian mode can be used in a jam. Fittingly the "you can feel good about Hood" jam is in Ionian. In these examples you can see how Trey and Duane both use the same scale in different ways.
Phish - Harry Hood
The Allman Brothers Band - Blue Sky
2. Dorian - The Dorian mode is a minor mode that evokes melancholy, yet soulful moods. The final note of the scale does not resolve itself, leaving one feel as though
there are questions left answered. Santana is an avid user of the Dorian mode. Here are two examples of the Dorian mode with Trey and Dicky (many people believe this part of the solo from the '71 Filmore show is Duane. It is not. I have watched the video, Duane comes in later. Dicky is very modal in his playing):
Phish - David Bowie
The Allman Brothers Band - In Memory of Elizabeth Reed
3. Phrygian - The Phrygian mode has a very dark Spanish/middle eastern sound. It is not commonly used in jam music, and it offers a strong contrast to the rest of the modes. It is also used frequently in metal. I won't post it, but if you're interested check out Yngwie Malmsteen's Heavy E Phrygian. Here is a more suitable example:
Jefferson Airplane - White Rabbit
4. Lydian - The Lydian mode is another bright and happy mode, but in a very
different way than the Ionian mode. Zappa was known for using it in his solos and Dicky Betts uses it very frequently. It has somewhat of a jazzy, unexpected feel to it, and so it works well in jam music. Here is an example of one of my favorite solos using the Lydian mode. It almost sounds as though Trey's notes are soaring through the speakers:Phish - Reba
5. Mixolydian - Jerry Garcia's favorite mode. It is commonly used in blues and rock, and has a bright feel with a dark side. It is an interesting sounding mode, and is often used in guitar solos. Here are two examples, one of Jerry, the other of Clapton.
Grateful Dead - Fire on the Mountain
Eric Clapton - Let it Rain
6. Aeolian - similar to the Ionian scale, the Aeolian mode is a natural minor scale. Thus, it conveys feelings of sorrow, regret and despair. It has a very dark sound to it, and is often used in Rock. Listen to this example by Jimmy Page:
Led Zeppelin - Stairway to Heaven
7. Locrian - The Locrian mode sounds very odd, and is not frequently used in jam music. If it is, I can't think of an example. The Locrian mode sounds dissonant, and spacey, almost wrong. The previous six modes are used most often in jam music.
Hopefully this has shed some light on how modes are used in jamming, and why they are so important. As you can see from the examples above, the modes are a strong tool and can be used to control the mood of the jam. The following is a video of Suzy Greenberg from 10-21-95 at Pershing Auditorium in Lincoln, NE. Notice how Trey plays the solo from Stairway to Heaven using the Aeolian mode at 2:45. Enjoy, as a bonus I've also included the Harry Hood from the same show. Notice Trey teases Beat It in both songs (as was mentioned a few days ago in this article).
