What exactly should I have to learn to understand why certain combination of chords are harmonic when played in a sequence?

Question

I'm pretty sure that there's a lot of theory in finding combinations that are melodical/harmonical. There must be a way to say that 3 different chords are likely to form music. That given 2 chords, the third must be X and so forth. The question is: What do I have to learn? I'm pretty sure it has something to do with harmony, but I'd really be happy to know what exactly in harmony would answer my questions.

Answer 1

First of all, certain combinations of chords are called a progression, not "harmonic". If you want to know which progressions seem to "work", and others do not, I can give you a kind of list. I use Roman numerals, where in the key of C I means the triad built on C, II the triad on D, III the triad on E, etc. So:

I is followed by IV or V, sometimes VI,less often II or III

II is followed by V, sometimes VI, less often I, II, or IV

III is followed by VI, sometimes IV, less often II or V

IV is followed by V, sometimes I or II, less often III or VI

V is followed by I, sometimes VI or IV, less often III or II

VI is followed by II or V, sometimes III or IV, less often I

VII is followed by III.

However I would caution you not to depend on this or any other sort of mechanical operation to achieve success. You should study music that you like, and see how the effects you admire are achieved.

The subject called "Harmony" is normally based on the procedures followed by Bach in his chorales (and other pieces). And this list is based upon those models. However Bach's procedures, however admirable, are not that useful in composing today, when standard chords and chord progressions are almost never used! That's why I encourage you to look at the music you like for pointers.

Answer 2

Depending on what you want to do with your music (and there can be many many many ways to go!), you might be good starting off with Functional Harmony. That is, every chord has a function. You want to get back to home, or Tonic function. Dominants lead to Tonic. Pre-Dominants lead to Dominants which lead to Tonic. Depending on where you are in your theory journey, you might have different chords in each function category. The basic one is:

III (no solid function) | iv | Pre Dominants: IV or ii | Dominants: V or vii0 | Tonic: I

As you go through the classical era and romantic era composers, you build more pre-dominant chords (as well as non Dominant to Tonic progressions). As you go through the 20th century composers, you build more dominant chords. So by the time you've finished theory courses, you've got a dozen pre-dominants and a half dozen dominants.

This is of course only looking at harmony as blocks. There are any number of ways to create STRONG harmonic lines using melodic lines to create the sense of movement, tension and resolution. Some of the color chords added to the functional harmony chart were created because the melodic lines said they work, and theorists figured out how.

But I'd figure out more fully what you want to be doing with these progressions in your music studies, and perhaps take a peek at the functional harmony pages on wikipedia and see if they help.