What exactly is ABCDCBA form?

Some people who try to follow my improvisation exercises don't understand the concept of ABCDCBA form. To help them get the most of these exercises, today I would like to make myself more clear what do I mean about this particular form.

The different letters here refer to different melodies or thematic material. If you look closely, although you can see 7 letters, in reality there are only 4 options - A, B, C or D (it's quite different from these 7 letters - ABCDEFG, isn't it?). The episodes A, B, C and D have to be quite different from each other - perhaps they all have different melodies, harmonies, tempos, meters, rhythms, textures and they could be performed using different registration.

Let's take a look at this structure (ABCDCBA). What do we see here? D is in the center, A is on the outside, then comes B and finally C. In other words, CBA in the second half is like a mirror version of ABC in the first half.

Therefore, one of the terms used to describe this form is Concentric form - meaning that in the center you have an episode around which there are mirror episodes of several other themes.

We could also regard this form as having a ternary structure - ABC-D-CBA. Then we could have something like compound ternary ABA form which could be the simplest example of concentric form.

Concentric form can have 5 parts - ABCBA, or 9 parts as well - ABCDEDCBA. The main idea is the mirror version in the second half around the central section which forms a nice symmetry.

I hope this explanation made the principles behind this form more clear to you and you can apply it in your 10 minute improvisation practice.