“I’m falling in love with the bass guitar. I don’t know why yet, but I think it has to do with it’s simplicity and purity,” sayeth Jeremiah.
I agree, but that’s only one of the things I love about the bass. I’m an improvisatory player. I enjoy living on the boundary between the groove, as it was written originally, and the edges of what’s possible. What’s so wonderful about playing the bass in this mode is the effect it has on the other musicians.
Say, for example, I’m playing a simple song in 4/4, and I change my phrasing at a certain point, so that I’m playing six notes for every quarter-note in the rhythm of the tune. First, the drummer has to decide whether he should follow me or not. He might hold back, or he might change it up with me.
Next, the rest of the band has to decide what to do. They basically have three choices: a) insist that nothing has changed, and stay in their rut (the rut of what they were already doing), b) go along with the rhythmic change, while playing dumb and not adding anything of their own, or c) adding their own idea — their own energy — to the changes, and helping the snowball to grow.
Then, 12 bars later, say I start adding extensions and leading-tones. I build the excitement in my own little part of the whole performance, and the audience, while they might not understand what’s going on, hears that the tension is building. The other people I’m playing with have three choices again — the same ones they had before: a) deny it, b) reluctantly go along with it, or c) support and build on the foundation.
When it’s working — when everyone plays together, allowing others to influence their own role, while also asserting their personal point of view on the music, a single song can build into a frenzy, and a set of songs can affect the audience in a permanent way. (I’ve seen it happen, from the stage.) The bass can be the most important part of the process, but only if the other musicians are willing to play along. If not, then the whole thing flops.
See where this goes? This is my attraction to playing bass. A bassist has the unique role of holding the whole band together, while at the same time creating the tension curve for the whole group — determining what’s most important at any given time. There’s still lots of freedom for everyone, but the foundation is clear at least some of the time, and if everyone is listening to each other, it’s clear most of the time.
But it’s still up to the bass to create the bridge between the meter of the song, and the harmony… That’s why it’s so simple most of the time. (And also those bass strings are darn big!)
Now, I’ve played with my fair share of guitarrists, keyboardists and horn players, but in most situations, even the greatest soloist doesn’t have the power to form the whole picture of a song or a set, that the bassist has, even when the bassist only plays quarter-notes. Listen to Joe Satriani to hear what I mean.
On the other hand, there are bassists out there that think they can drive the whole show without the direct participation of the rest of the group. Mr. Big is an example of this. (Sorry for the 80’s references, but I’ve been out of the music scene for a while. 
)
For a bassist who really makes it work, listen to Tina Weymouth (of the Talking Heads) — she’s no great technician, but man, can she hold down a groove. And when the band needs her to drive, she drives it, and doesn’t stop ’till it’s over.
Anyway, I’ve gone on for far too long, and you can make whatever metaphor you will, but I’m telling you that the bass is where it’s at.
(BTW, I don’t mean to knock guitar players — there are many great leaders who play guitar. Check out Stevie Ray Vaughan and Jimi Hendrix for a couple of clues. As for keyboard, Billy Joel and Elton John come to mind…)