Traditionally, the modes didn't transpose (we're talking medieval music) so music theory has been hugely in the total series. Further, modes are kind of limited to 7 scales, all built around the Major scale pattern (Ionian, for purists). Tonal music uses more Baroque, Classical, and Romantic concepts of the major and minor scales. And it's quite arguable that other than the very liberal 20th century composers, most of the popular music on the radio waves are descendents of the tonal series.

And yeah, piano's the way to go for a general sense, though I've been learning theory the way a person working with a fretboard (guitar, mandolin, etc) learns, and it's quite a different take on the rules I know already from my piano theory.

Also, from personal teaching, I have students that don't play piano, but rather just a string instrument or even a wind. They need to have supplementary knowledge, such as techniques (string has up-bow vs down-bow, pizzicato, etc.) or a viola student will need to work with the alto/viola clef. I have a couple students that know how to read treble, bass, and viola clef, and they're on the beginning book. Rather impressive compared to others that learn just treble and bass and they're in the advanced levels.

All I can say I am yet to hear a piece of atonal music that I really thought was pleasing to the ear. Even 12 tone music seems very grating on the ear.

Very true. There are two schools of thought there-

The first is that our ears have been trained to hear tonal music from the music from about 1400's to about the early 1900's. Atonal music and music using things such as quarter steps has sprung up. Because this is new to our ears, we don't care for it, similar to any new variety of something - food, art, etc. It takes time to adjust.

The other school of thought is that people like the ones we have now because they do sound good and aren't full of dissonances. The octave is a nice 2:1 (1:2) ratio. This is pleasing. A perfect fifth is 3:2. These are relatively simple. The more dissonant you get, the crazier the ratios. A perfect fourth is 4:3, while a minor second is 16:15. The most dissonant interval of the 12-tone language is the tritone (augmented 4th / diminished 5th). This is a ratio of 45:32 or 64:45. With the numbers alone, it's easy to see why dissonant intervals, and therefor atonal music, doesn't work well.

Further, researchers have found that newborn babies, when played lovely basic two-note harmonies, such as a perfect octave or perfect fifth have been relatively passive, but when played more dissonant intervals have been found to have elevated heart rate, and have become more uncomfortable. We're talking newborns here, so there's something to be said about nature vs. nurture.

As far as the realm goes with "we're just not used to it yet", a terrible argument is "we're not used to eating rat poison either". ;)

Well I'm around an intermediate level guitarist. I know a bit of theory but I'm really a beginner when it comes to that. So what I'm looking for is a beginners to music theory for guitar, or guitar theory I guess is what I should say. I don't want to be a composer, I just want to know they theory behind guitar.

Sadly I don't know much about guitar theory books. The one I'm using, I do recommend, but it's kind of a tunnel-vision recommendation; it's all I know. It's called Fretboard Theory by Desi Serna. It goes from teaching you the pentatonic scale and chord shapes, which are the huge basic building blocks of creating any scale and chords.

When you boil it down, guitar is just the sum of scales and chords. If you know your patterns, you can move them up and down the fret board and recreate them in any key, and it'll work well. This book's approach is nice because it tells you how it all ties together as well as gives you plenty of examples of popular music which show each topic discussed.

One does not simply start listening to 12 tone music. Most of the well known pieces are far removed from traditional convention so you need to look for it in its milder forms. Order is not demanded by the object, but by the subject, it's only through exposure that you'll find coherence in the more intemperate forms.

Can you give an example of what sort of theory you're looking to grasp? Just basics on voicings and how the notes and chords relate (something I can handle)? Or something more substantial like how chords and scales are actually formed and stuff about modes (something for GB)?

I honestly don't even know. I want to learn everything from the basics to the more complex things.

I'm not satisfied with just knowing scales and chords. Like you said, I'd like to know how notes and chords relate And how chords and scales are formed. I want to know everything from a to z. I know that's a big order.

I've been waiting for one of these threads. Hmmm..

Are there any harmonic functions that sound pleasing to the ear outside of I, ii, iii, IV, V, vi, vii (or dim)?

I do know that there is a function where the dominant of the minor scale is turned major or dominant 7th, but are there any harmonic patterns that give a really good cadence and progression with 9th's, 11th's or even better #5 or #6 chords?

Staccato. If it is played loud and fast it can also be called an accent.