Chord progressions fluctuations

Question

I'm sill in the learning process for chords progressions, so I'm sorry in advance if my questions are simplistic for some advanced musicians.

I've watched several harmonic analysis (Youtube, websites...) of classical music (Moonlight sonata, mozart...) and it would appear to me (correct me if I'm wrong), that progressions can switch from one mode to another, starts on triads and then introduce augmented 7th, or else...I'm not talking about modulations here.

Am I right to assume that mode (ionian, dorian...), scale, chord type (triads, augmented...) and of course modulating key can always change in a progression? And of course on the top of that you have all possible inversions.

Also, I've noticed that sometimes you have 2 chords for a bar, one for the left hand and for the right hand? So we can combine or superimposed chords when they share enough common notes? Is that correct?

Any help on this would be appreciated.

Thanks

Answer 1

Yes. There are some general rules that are followed when producing harmonic progressions, influenced by style, time period and other considerations. Common Practice harmonies vs. Jazz harmonies as a comparison. The analysis of these progressions generally follow the rules of the style being analyzed.

When adding harmony to a melodic line, different chord choices can be made for the same melody, depending on what style you want the harmony to sound like, what mood you are trying to achieve or what transitions or modulations you are progressing towards.

As a more simple example, if my melody consists of alternating notes F and A, I could harmonize the line with either a D minor chord (D - F - A) or an F major chord (F - A - C). Both will add harmony with different effect.

You will see extended chords that can look like two separate chords put together, especially in Jazz and modern music.

Answer 2

Yes, you can have two chords at once. Depending on the chords, the effect of combining them can be added alterations/extensions to one chord (or the other) or a Game of Thrones-ish struggle for tonal supremacy, or bitonality and sometimes a train wreck.

Yes, you can combine chords with common notes, but that's kind of not the point if you're after new sounds. The magic for chords with common notes lies in in substituting one for the other. As a rule of thumb, if two chords have two or more notes in common you should (according to taste) be able to substitute one for the other.

Slash chords are the simplest way to introduce harmonic tension between the left and right hand parts; the bass note is telling your ear one tonality while the right hand chord is pulling the ear in a different direction. Note that a slash chord like D/F# is really just an inversion of D major, whereas D/C will sound more exotic.

There are some practical considerations in superimposing chords. Unless you're after a horror movie vibe, the lower LH notes need to be widely spaced to avoid muddiness, and consideration could be given to omitting some notes from the LH chord.

Answer 3

Yes, Western music broke away from sticking in one mode for a whole song several hundred years ago - though of course you're perfectly at liberty to do that if you like!

You may have been taught what chords use the notes of what scales, maybe as a basis for simple improvisation. That's fine, as far as it goes. But it's not a set of restrictions. As you have noticed, real music uses a much more extensive harmonic language!

Don't worry too much about the LH and RH of a piano part having what look like separate chords. They MIGHT be 'polychords' a particular technique of stacking two different chords. But most likely it's all one harmony, just played by two hands.