Memorization is much easier once you start to recognize certain chord patterns that occur over and over again in jazz - you'll be able to memorize phrases and sentences instead of letters and words, if you will. This will get you going in that direction, with the example of Miles Davis' jam classic, Solar, as an illustration.

Here are the chords to Solar (every major chord below should be understood as a Major 7th):

|   Cm  |   Cm   |   Gm   | C7     |

|   F    |   F      |   Fm   | Bb7   |

|   Eb   |  Ebm - Ab7 | Db  | Dm7b5 - G7+ | 

Principle 1: Most alterations reduce to 7

This is a key ingredient to memorization. You emphatically don't have to memorize all the nitpicky little extensions  (such as 9, 13b5, 11, etc.) that you sometimes see in jazz charts. Once in a while, a chord alteration is critical to the feel of a chord, but often the alteration is only introduced into the chordal notation in order to accomodate the melody note. Great guitarists such as Joe Pass and Jimmy Bruno can be found on their (excellent) instructional DVDs saying things like: "there are only 3 main types of chords: major (or major 7th), minor (or minor seventh), and dominant seventh chords. Don't take chord symbols that literally - when you see a dominant 7th chord, play an alteration: a 9th, 13th, or whatever seems right."

I think this advice is generally right, with a few caveats:

• In addition to the 3 main types of chords mentioned above, augmented and diminished chords are also fairly common. Although you can, indeed, think of both of these as altered 7th chords, it's often better to think of them as augmented or diminished, because their "flavor" and scale implications are so strong. (A Bb diminished chord can be thought of as an altered A7, for instance, and an augmented chord is basically a 7th chord with a raised 5th). In terms of memorization, you will rarely try to memorize a diminished chord as such, because diminished chords are almost always passing chords in larger patterns that you will know.
• There's also that half-diminished chord, otherwise known as the m7b5 chord, which has a unique character and almost always appears as the ii chord in a iim7b5-V7alt-i pattern when you're in a minor key.

The Chord Pattern Dictionary - Part 1

Let's start establishing a pattern dictionary - there are a handful of chordal patterns that show up in jazz again and again.

Two Chord Mini-Patterns

First, there are several mini-patterns for chord changes - suppose you're playing a chord, and you don't know what the next one should be. Now, if you're going to take a WAG (wild-ass guess) at the next chord in a jam, it might be a good idea to keep it at a pretty low volume until you know whether you're right or not. However, let's talk about the relative frequency of "binary" (two-chord) mini-patterns.

1. Up a fourth. By far the most common pattern in jazz and, indeed, most Western popular music. The very common ii-V7-I pattern consists of two repetitions of the Up a fourth mini-pattern. The B section of a tune, if there is one, seems to begin on the chord a fourth up from the tonic (the main chord of the A section) at least 75% of the time! The first chord change of a standard 12-bar blues for is almost always a move up a fourth. In Miles Davis' Solar, for instance, there are 12 chord changes (counting the change from the last chord of the turnaround back to the first chord at the top). Of these, eight!!! of them are up a 4th (and two more of them are the next pattern, leaving only a tiny bit left to memorize that's not in either pattern).
2. Major to minor - major chords often turn to minor, turning a I into the ii of a ii-V7-I. It's a way of modulating to the key a whole step down. In Solar, this happens twice: the Fmaj7 in bar 5 goes to an Fm7 chord in measure 7, and then Ebmaj7 goes to Ebm7.

Patterns

This is just a start on patterns. Please add your own in the comments if you have some.

1. Of course, if you have played much jazz at all, you know that the ii-V7-I pattern is everywhere. In fact, it's so pervasive that we mostly don't even have to memorize it - we just follow along.
2. In minor keys, the analogue to ii-V7-I is iim7b5 - V7alt - i. In my experience, the preferred alterations (but not the only) for the V7 are augmented and 7b9.
3. ii-V7-I patterns are often used sequentially, connected by the Major-to-minor minipattern. In fact, Solar is almost entirely composed of this. Everything in Solar, except for the first 2 measures and the move to the turnaround (measure 11 to 12) is composed of this pattern!
4. The last measure or two of a piece is always a turnaround leading to the I or i, and it's usually pattern 1 or 2 above.

Putting it together - learning Solar with Patterns

There are only two easy things you need to remember in order to memorize all 12 chord changes in Solar, in any key!

1. The first chord change is from i to v (Cm to Gm). This s a pattern we haven't yet discussed - it's really a roundabout way to get from Cm to F major. Normally a Cm tonic would go to an Fm as its 4th degree, but the move to the the Gm, which fits just fine in a Cm scale, sets up the modulation to F.
2. The song basically follows pattern 3 above.

You shouldn't need to explicitly memorize the fact that, at the end of the form, the Db goes to a Dm7b5, because the turnaround to the tonic is almost always present in jazz tunes, and the fact that pattern 2 is used here is almost required, since the tune is in a minor key.

Well, what do you think? Are these principles helpful? Can you analyze and learn other tunes successfully with it? Can you play the Solar chords from memory? Can you play it in Ebm without writing down the chords?

- Warren