Yes, there is an optimal amount of theory: enough to help you understand what you are playing or trying to accomplish with music.

I love discussing music theory! Especially clearing up misconceptions about it. :) So I'm going to address each one of your great questions & observations. But I'm starting by offering this defintion that answers most of them:

Music theory is a set of concepts that describes the sounds that happen in music.

If you apply & follow that defintion to it's logical conclusion, most of your questions are answered & any possible confusion cleared up!

Music theory is not a list of rules that tell you what notes you are allowed to play, or not allowed to play. Music theory is simply a means of identifying the relationships between the notes you choose to play; whatever those notes may be. This makes it possible to objectively identify them for conceptual clarity & have a common language with which to communicate with other musicians.

Addressing specifics!

Originally Posted by: dlwalkeBut for rock music in particular, I wonder whether or not, or how rock would have evolved if the musicians who developed it had first gotten a good solid grounding in what music theory say's works.[/quote]

This is kind of begging the question: how do you know what works? What does "works" mean in this context?

The answer is: if you like the sound of the notes you are playing, then it works for your purposes. So, any musician (rock or otherwise) that doesn't have a complete degree in music theory is:

1. Already relying on an existing body of knowledge (functional instruments, notes, scales, chords), learning from it, using it to some degree, even if they don't know the technical terms for what they are doing.

2. Experimenting with those existing elements & creating sounds they like. And that's perfectly valid with or without the ability to identify what they are doing in terms of music theory.

Originally Posted by: dlwalkeWould too much adherence to classic music theory have constrained what was done?[/quote]

No. But it certainly could have an effect on the resultant music. Obviously musicians can only play what they know or have worked on.

Consider that Chuck Berry was well versed in blues, jazz & country music prior to his rock career. He even started his career trying to incorporate more "sophisticated" musical elements in his songs. But what went over for him, what really sold well was his stripped down, straight ahead, energetic 12 bar blues form rockers like "Maybelline" & "Johnny B. Goode". So he stuck with that for most of his career, performances & recorded output.

But check out this clip from the documentary on his life.

https://www.youtube.com/watch?v=ZL7fy5v_PKg

Chuck's well was much deeper than most people knew. But he knew what he liked, what worked for his audience.

Consider Queen. Freddie Mercury & his bandmates were certainly versed in music theory elements enough to create "Bohemian Rhapsody". There's no way they could have created that masterpiece without a certain level of theory knowledge.

Originally Posted by: dlwalkeI have read for example that alot of rock uses chords with roots from the diatonic, or a pentatonic minor scale, but with a lot of freedom as to whether or not those chords are really in the key (e.g., minor vs major, or ubiquitous use of dom7 chords that aren't really in the key).[/quote]

Modern classical music in the late 1800s & early 1900s was already & still is far beyond anything done in rock music regarding experimental freedom of use in musical materials. Using any & every chord or scale willy-nilly, playing in multiple key signatures at the same time, playing in multiple time signatures at the same time, playing minor & major in unrelated keys, playing them at the same time, trying to be as dissonant & as unconventional as possible.

You name it & it was already being done decades before any rock musician did anything remotely like it.

Originally Posted by: dlwalkeI believe that music theory can be both descriptive and prescriptive. Did music theory catch up to rock?

Music theory is only descriptive.

Its only function is to describe the sounds that happen in music. The sound is first. I suppose someone could use it prescriptively in the sense that thinking about it might help someone think of something to try that they haven't yet tried to play. And then they can decide if they like the sound of it. :) But the only reason that the concept exists in the first place for a musician to think of & try is because that music theory idea, concept or term exists in order to describe a physical sound that happens.

This might help clarify some of your questions.

And music theory & practice was well beyond rock before rock even existed. :)

[quote=dlwalke]That is, was a lot of rock not really based on music theory and may have indeed violated some principles and then music theory started working on why some of that actually sounds good? Maybe not. I don't know. Just wondering really.

This is a great question & observation!

The mistake you are making here is that there is no such thing as music that violates music theory. Theory only exists to describe the sounds in music. So if you make a musical sound, then you look for an existing music theory term to describe it. Or you create a new music term to identify & describe it.

To be clear, there are certain accepted practices of chord progressions & voice leading that are taught in music schools. And if you are working on a degree in music you will discover that certain historical composers used certain types of voice motions in certain ways & not in other ways. Some of those old methods are still used to this day. And the reason is because they sound good. :)

Unfortunately, these are sometimes regarded as "rules that must be followed". But they are really only codified practices of certain individual composers. And it should be obvious once you get to studying composers beyond the classical era that those "rules" don't have to be followed, because they weren't! In most cases they were intentionally disregarded.

[quote=dlwalke]

I was noodling around the other day and was surprised that the following progression sounded quite nice: D(D form)->F#(E form at 2nd fret)->G(G form at 3rd fret)->A(any position).

Let's stop here & make a few observations.

1. The act of identifying a chord is the use of music theory.

2. The act of identifying the interval distance between certain chords is the use of music theory.

3. Mentioning that a chord is borrowed from a key is using music theory.

4. Mentioning that a chord could resolve in a certain way, but doesn't in this case is using music theory.

Music theory doesn't tell you that you must resolve the F# to B. It only says that those chords have a certain relationship & in this case you have chosen not to play the resolution. That doesn't make you wrong or breaking a rule.

The sound comes first, then we use music theory concepts & terms to identify the sounds for the purpose of understanding.

[quote=dlwalke]I wouldn't have come up with that based on the little I know about music theory. Maybe if I knew more about music theory I would have though. Well, I've got a lot of time on my hands to think about these things I guess.

This is a great observation & an important learning moment. Learning theory & training your ear are two different things, but they need to grow together.

Just because you know the music theory formula for a scale or chord progression doesn't mean you know the sound of it. You have to practice a lot to get those sounds in your mind solidly & then you can connect them to the related concept in your mind. Conversely, just because you know how to play something you like the sound of doesn't mean you know all the theory involved or that it might imply. That also takes time & effort!

That's why I am always stressing to GT students that it's important to keep your theory understanding & playing ability on par with each other!

Fun topics, thanks!