I was listening to several pieces by Stravinsky in the last couple of days and while his harmony is inventive, fresh and stimulating, it is, compared with the best examples of common practice harmony, crude and harsh to the ears.
This is all prompted by reading a post on Luke Dahn's blog. He is an excellent theorist and wrote a fascinating post about the possibility of using one piece of music as material for teaching everything there is to know about chromatic harmony. The piece he chose is the masterpiece by Schubert, the song-cycle Die schöne Müllerin. Luke has prepared a beautiful chart showing just what harmonic devices Schubert used in the songs. Here is the link. I can embed it here as well:
But it is much more legible if you follow the link. This is a beautifully graphic analytic overview--the kind of thing I might do if I were teaching a theory course! You can download the complete score here. And here is a complete performance by Dietrich Fischer-Dieskau and Gerald Moore with the score. It even includes the poet's prologue:
So you can, through the wonders of the internet, give yourself a complete course in chromatic harmony taught by Luke Dahn, with the aid of Franz Schubert. How, exactly? Well, let me walk you through the first song. First, go download that score from IMSLP (what a wonderful resource!). Then print out the two pages of the first song, Das Wandern. Now, let's have a look at Luke's chart. As we can see, Das Wandern is in the key of B flat. That is shown in Luke's chart by the "Bb:" at the beginning. This is a very simple song and the only harmonic device he shows is the little purple "V" in measure 13. The purple indicates that this is a "tonicized key area". Tonicized? Whazzat?
What Luke is teaching is not the most basic level of harmony, i.e. all those chords that are a normal part of the key, but rather chromatic harmonic, that is, all those devices that use accidentals, chromatic alterations, to either strengthen chords that are in the key, as the augmented sixth chords do, or to intensify certain chords by "tonicizing" them, i.e. making them momentary tonics in their own right by using secondary or applied dominants. Let's look at the Schubert song to see how this works. The song is in B flat. In measure 13 (you have numbered your measures, right?), which is the first measure on the second page in the score I downloaded, we see this:
Looks ok--hey, wait a minute, what is that F# doing there in the bass? That's the chromatic part. In order to temporarily make a chord into a tonic that is not the tonic in the key, Bb, we have to use an accidental. In this case the F# is the leading tone in the key of G minor, which is the relative minor (meaning it shares the same key signature of two flats as Bb major) of Bb. This makes the last harmony of m. 13 into a dominant of G minor, what we would analyze as a "V6" of V (V6 because the F#, the third of the chord D, F# A, is in the bass). Now go and listen to the song and see if you can hear this momentary departure from the key of Bb--it adds harmonic richness to the third phrase, creating the climax of the song. Incidentally, this tonicization forms the first part of a sequence, which means that the same idea is repeated at a different pitch. The tonicization, using F#, of G (minor) is followed in m. 15 with the tonicization of the dominant ("V of V"), F. This is done with its leading tone, E natural.
In the second song, Wohin?, we get not only more tonicization, but also, in mm 38-40, use of the Italian augmented sixth chord, shown with a little Italian flag. You can read up on augmented sixth chords here.
That should get you started!! With all the resources available online these days, anyone who actually wants to learn about music, can do so---for a song!