connosance and dissonance (sp?)

The idea of consonance and dissonance isn't very complex, even though there's an awful lot of complex discussion about it.  Contrary to popular belief, it doesn't mean specifically the way that tones sound together... it refers to whether or not the interval or chord sounds complete by itself.

The dominant 7th chord is a good example of a dissonant sound -- it wants to 'move' somewhere.  A major chord, on the other hand, can hang there all by itself without needing to resolve to something else, so it's a consonant sound.

You can slice things up a lot more precisely if you'd like.  The intervals of perfect unisons, perfect octaves, and perfect fifths are considered 'perfect' consonances.  

Major and minor thirds and sixths are considered imperfect consonances, which are slightly less stable.

The seventh intervals, and any altered intervals are considered dissonant.

Perfect fourths go either way -- they're considered imperfect consonances (or even dissonances!) if they stand alone, but perfect consonances if they are supported by a third or fifth interval below (so A-C-F is perfect, as is F-C-F).

This is actually one of the areas of theory that's still evolving; modern compositions are treating some dissonances as consonances... and when you get into atonal composition, there are no dissonances, since there's no tonal center to move towards.

Tom

Thanks, tom, that really un-muddles everything that Ive heard thus far. Now I can read in less confusion than before. (just enough to keep me learning)