The jam sections of “Runaway Jim” and “Twenty Years Later” share similar improvisational parameters, though they sound nothing alike. In “Runaway Jim,” the first parameter is the recurring six-measure phrase-length pattern, a metric/temporal problem. The second is the descending riff, a melodic/harmonic problem. They go hand-in-hand. (I’m tempted to say they’re inseparable, but that’s going too far.)
The first problem is how to (or how much to) acknowledge (if at all) the end of the six-measure phrase and the start of the new one. Sometimes Phish improvises strictly within the six-measure phrase pattern for the entire jam. They acknowledge it all the way through. Sometimes they ignore it completely. Often, both strategies pop up in a single jam. But the second approach, losing the phrase, is more rare than the first, I believe.
The melodic/harmonic problem, or the riff, is largely a problem for the bass. The bass player has to decide how close he wants to stick to the descending riff. He can play it note-for-note. He can vary slightly. He can vary wildly. He can go back and forth. Each strategy, or combination of strategies, affects the collective improvisation in different ways. (Playing the actual riff is crucial, however, as a way to signal the end of the song. It’s a ripcord measure, one of many.) A “Runaway Jim” type of jam requires the bass and drums to be relatively disciplined (or not), or else things could fall apart. Unlike, say, early-’90s versions of “Tweezer,” when falling apart seemed to be one of the jam parameters.
The two governing parameters of the “Twenty Years Later” work much the same way as the two “Runaway Jim” parameters, even though the two jams don’t sound anything alike. There’s a temporal/metric parameter (a 10-measure phrase length, as greatfuckingbird suggests) and a melodic/harmonic parameter (a riff, mostly carried by the bass).
The first problem is how much to acknowledge the end of the phrase, and the second is how close to stay to the riff. Both parameters in “Twenty Years Later” are more complex, I think (10 is more complex than 6, and the riff is longer), and therefore more restrictive than their counterparts in “Runaway Jim.” (Thankfully, the tempo is considerably slower.) Again, in terms of the melodic instruments, the guitar and piano get to play more freely than the bass. (There are jams where the drums can play just as freely as the melodic instruments, but because this is rock music, there aren’t that many. That stuff’s more at home in certain jazz idioms.) As jams, they are relatively tightly wound. If the foundation gives out, it falls down. Other jams (“Reba,” “Bowie,” “Melt,” “Antelope”) have relatively more global, or general, parameters. Perhaps that’s why they are given special treatment in sets.
The improvisational problem in “Stash” is primarily harmonic. Phrases are grouped in four throughout, which all but removes the metric/temporal parameter from consideration as an improvisation parameter. (You could say the quick tempo and constant eighth-note “motor rhythm” are parameters of sorts, and you wouldn’t be wrong.) The chord progression of the jam consists of four repeating sonorities, a variation of i-VI-ii-V in minor. It’s a common “turnaround” progression.
The basic problem is how to improvise in an interesting manner, collectively, over those four chords. The beauty of the problem, and probably why the song stays in the repertoire, is its simplicity. You can ignore the progression entirely, like living next to a train station. You don’t hear it after awhile. Because the problem is elegant, it allows for wild, free exploration. Strictly interpreted, it’s incredibly restrictive.
Once the realization sets in that i-VI-ii-V is, in fact, i, all restrictions (if you want them to be). It’s the difference between locking someone in a house (“Foam”) and locking someone out of a house (“Stash”). Within a single “Stash” jam, Phish will move from one approach (acknowledging the progression and trying to create beauty within it) to another (recognizing it’s all one big chord/mode, like “Bowie,” “Antelope,” etc.), all without resorting to a Type II strategy. Like “Runaway Jim,” “Twenty Years Later,” and bunch of other jam songs, you pull the ripcord by playing the chords again, signaling the end of the song.
Are there others songs that can be added to the “Runaway Jim”/”Twenty Years Later” type? The “Stash” type?