effect of music teory on modern music

Like a lot of things, it depends on how you look at it.

A modern pop song - verse, chorus, verse, chorus, middle 8, verse, chorus, chorus fade equates to this in formal analysis: ABABCABB

Sonata form equates to ABABCAB'CAB'

So you can see the similarities and how you can use formal analysis to talk about music.

Harmony is different. It's changed over the centuries - musica ficta, counterpoint and other Renaisance tools, avoidance of parallels in the Baroque and later, and the use of I, IV and V in the classical period (just like I, IV and V in modern blues in fact) - but the important thing is that if you know how theory works, then you know how to tweak it to make it fit what you're writing today.

If you play a chord with the notes D, E and F# it's going to sound edgy (Dadd9). Add a C to that chord and you have a jazzy D9. Knowing that ii in a ii-V-I jazz sequence is a minor chord helps your sequence sound like it fits. Knowing that ii is routinely used as a substitute for IV (basic classical period theory) gets you to some of those in-between harmonies and your ii-V-I sequence can suddenly become a brighter IV-V-I.

Yes, most rock songs these days use a riff (rhythmic motif - see Beethoven's 5th) but you can play the unplugged version of Layla (chords) alongside the full-blown electric version (riff) and by doing so you can see how the underlying (implied) harmony in the electric version hangs together.

So, don't dismiss the theory studies. You'll use it more than you think.

Learning music theory will make you a better musician for every and any kind of music - period.

Insights and incites by Notes

Music theory is a pretty broad field. You can break it down into smaller elements, each of which has its own uses.

Basic music theory (also called the rudiments of theory) gives you a grammar to work from, a way to communicate with other musicians. Knowing what notes make up a given scale, or how to interpret a key signature, or count a rhythm... those are all basic skills. Every musician should acquire them.

Counterpoint studies the interaction between melodies. Some interactions are more interesting than others, which is why traditional counterpoint studies restrict things like parallel perfect fifths - it suggests there's a more interesting way to construct your second melody. But you're absolutely right, each genre has its own idioms - what's taught in school is usually 16th century counterpoint (based on the masses of Palestrina), with some classes including 18th century techniques like chromaticism (based on the keyboard works of J.S. Bach). If you follow the rules you'll write things that aren't objectionable - but you won't write anything brilliant. In fact, ALL of the works of both Palestrina and Bach break at least some of the "rules"! So just think of them as guidelines - they're very useful as an editing tool if you're not happy with a section of something you wrote, but they shouldn't be your starting point unless you've got writer's block.

Basic harmony looks at the progression of chords. It's extremely useful to be able to recognize a chord tension and know how it's likely to resolve - that a G7 can lead into a C root chord. That's always useful for a musician. More advanced harmony is really an extension of counterpoint - the reason you'd use a 64 voicing in a particular place is the relationship between the bass and soprano. Recognize where the various inversions are used in relation to the outer voices and it'll suddenly make a lot more sense. I really wish my teachers had spent some time pointing that out!

Form and analysis let you see how composers have structured pieces to keep a listener's interest. If you just strung together a bunch of brilliant musical ideas, your listeners would get lost, because they need a frame of reference. Studying how phrases build periods, periods make sections, and sections relate to and contrast each other gives you a framework to work in. It's less important to know what a Rondo is than it is to understand you've got one main section repeated, with contrasting bits in between. Think about this stuff as structure - if you wanted to write a poem, one of the first decisions you'd make is whether it's going to be a sonnet, a haiku, a limerick, or whatever. That doesn't tell you what to write, but it gives you an outline so the finished product will make sense.

Composition techniques are about transformations - since you want your sections to give contrast, but still relate to each other, you don't want to keep adding new ideas - you want to make the old ideas fresh and new, showing them in another light. So how can you take the stuff you've already written and turn it into something else? Not only will this give you tools to keep a piece coherent, over time you'll find that using these tools makes you efficient - you see logical possibilities.

The problem is that each of these sections lay out "rules", when they're not really rules at all. Even in something as simple as the rudiments teachers will say "the top number of a time signature is the number of beats per measure". That's usually true, but not always - 12/8 time has four beats, not twelve. So when you get to compound time, you learn the "except for" situation. Parallel perfect fifths are forbidden in counterpoint, but Debussy's works are loaded with them. The "except for" is that the parallel fifths usually occur in the inner voices, with the outer ones moving in contrary motion. Notice I said "usually"... because the "except for" stuff isn't a refinement of a rule, but an attempt to explain something that breaks the rules but sounds good anyway.

And that's the basic truth behind all music theory: it comes after a composer uses a technique, not before. Palestrina used some parallel fifths, but so seldom we could write them off as an aberration when he got stuck. Debussy did it so often we needed the "except for".

Learn the "rules", pass your courses, internalize as much as you can. Then do your own thing - you'll find that the theory stuff really does give you a good foundation to build on.