what in the individual (is is an emotional thing? Physical? Psychological?) drives one's like of certain songs and dislike of others?
Well, It's a complex thing. I've pondered this same question many times myself.
Physical
I like heavy drums. Not "you can hear it at the stoplight from 16 cars back" heavy, but more like the intro to Enter Sandman by Metallica. I like them because I can feel it in my chest on every drumbeat and I find it pleasant. Some sounds can also affect certain people in a negative way physically, such as nails on a chalkboard. That is why people describe it as "running up their spine". It sets up vibrations in their bone structure that literally does.
emotional
The emotional response can be to either to the lyrics or to the music itself. Listening to and understanding the lyrics to The Leader Of The Band by Dan Fogelberg could move the heart of anyone who understands why their father brought them up the way they did.
On the other hand, the second lead in Comfortably Numb by Pink Floyd will grab you emotionally from the first note and just hold you there for the duration.
Psychological
I think Monkeyleg summed it up pretty well. I would add that music can also change our "phychology" albeit temporarily. That's why we have driving music, music that we relax at home with, christmas music, etc...
I would like to point out that most music that seems to remain popular year after year is very simple. A simple rythm, simple harmonies, easy for the non-musician to understand. After all, most of the masses don't want to think about anything more complex.
I talking about one's personal response to the songs or music: what in the individual (is is an emotional thing? Physical? Psychological?) drives one's like of certain songs and dislike of others?
For me, it is either songs that have a mood that is reflective of my general outlook on life (somewhat of a depressive) or diametrically opposed to that outlook. For example, peices in line with my outlook are:
Nine Inch Nails: The Great Below & Hurt
DJ Tomcraft: Loneliness http://www.youtube.com/watch?v=RSf2uuwkZZc
Iron Maiden: Run to the hills.
Opposed to my outlook:
SFX: People can fly
Jethro Tull: Bungle in the Jungle
Artist Unknow: The piece of opera that the character Andy Dufran played in the film "The Shawshank Redemption".
For me, its mostly emotional.
Learn to identify the elements of music (melody, harmony, etc). They're fairly hard concepts to grasp properly. At least that's what I've found. If you do learn what these concepts are and how to identify them in the songs you hear, then i bet you'll understand the difference between Saturday in the Park and Layla vs Beginnings and Keep on Growing.
I can pretty easily identify the different elements in music, considering that I took piano lessons from the ages of 6 to 16, including lessons from a piano performance undergrad student, and I still study tons of stuff about music in my spare time. So, I do understand the differences between the songs I listed in my first post.
I'm wondering why the different elements put together in a certain way in a composition appeal to me, but if you put those same elements together in a different way I don't care as much for it anymore. What inside of me influences that? What inside of me subconsciously influences my preferences? Is that even knowable with the current level of scientific knowledge available today?
For example, the first time I heard the opening riff of Layla, I was hooked on that song before the song barely got started. Yet, I have found that I'm not necessarily attracted to other songs with similar opening riffs (similar in key, melody, harmony structure, rhythm, tempo, orchestration, etc.). Why?
Or maybe I'm just thinking too much and not making any sense at all.
Maybe I should just stop trying to figure out why and just enjoy.