Another way to put this is that for most pop music, you could often degrade gracefully to three triads of major or minor quality.
But even for something discussed previously on HN-- the Beach Boys "God Only Knows"-- this doesn't work. Wilson really wants a half-diminished seventh chord at the high point of the melody. One could perhaps degrade to a diminished triad in the accompaniment, but he's literally singing the seventh of the chord so it's there regardless. Substituting a major or minor triad there is a qualitative change and sounds suspicious.
If you're making your own instrument you might want to be aware that there's a "suspicious" sound that some types of consistent chord substitutions can have on certain classes of instruments.
For example, a bagpiper can make severe simplifications to the harmony or even change melodic intervals to fit what they have available. Audiences generally accept this because the strictures of the instrument have made that a common practice. (Even if you're unaware of the strictures, you've probably gotten used to hearing the result of the common practice.)
However, if one consistently employs major/minor triad substitutions on the guitar people are eventually going to hear that as a lack of quality. As in the Beach Boys example, this will often happen during key points. The guitarist may get lucky if the singer happens to fill out the missing note of the chord-- e.g., guitarist plays a minor triad and the singer fills out the seventh at the beginning of the chorus of "Last Dance with Mary Jane"-- but eventually the audience will figure out that the guitarist is missing a vital skill.
Anyway, unless your instrument is so novel it doesn't have any associations with extant instruments, make sure you have some kind of "escape hatch" so that skilled performers can play the chords they need. :)
Francis Rossi, of Status Quo fame/notoriety, depending on who you ask, quipped when presented with some award or other - "Wow! Twenty-five years. Three chords. Thank you!"
I love it when people do not take themselves too seriously.
Look, I'm just a caveman. I fell in some ice and later got thawed out by some of your scientists. My primitive mind can't grasp these concepts.
But there is one thing I do know:
When composers want to emphasize the chord they're about to play, they will often choose a new chord consisting of notes within a step or half-step of the original. And they will quickly play that new chord as a way to smoothly introduce the chord they wanted to emphasize.
Whether it's Mozart in the retransition of the G minor symphony, Wagner in a transitional phrase of the interminable Götterdämmerung, or a folksy award winning singer-songwriter, that new chord counts as a chord. And that new chord must be added to the sum total number of chords used in the song.
Thank you.
Edit: the Mozart chord is G-G#-B-Eb, as a kind of "neighbor garbage chord" of a dominant seventh in G minor. For Wagner, I can't remember what key it was in, but it's a half-diminished seventh chord with a pedal-tone a minor third below the root. It's function is as a neighbor chord to a dominant seventh built on that same pedal-tone. Not sure about OP's reference but I bet I could find an interesting transient chord in there, too.
Edit2: Oh yeah, the Wagner reference is indeed Wagner, so you can be sure it gets sequenced with at least three iterations in case you missed it the first time.
But even for something discussed previously on HN-- the Beach Boys "God Only Knows"-- this doesn't work. Wilson really wants a half-diminished seventh chord at the high point of the melody. One could perhaps degrade to a diminished triad in the accompaniment, but he's literally singing the seventh of the chord so it's there regardless. Substituting a major or minor triad there is a qualitative change and sounds suspicious.
If you're making your own instrument you might want to be aware that there's a "suspicious" sound that some types of consistent chord substitutions can have on certain classes of instruments.
For example, a bagpiper can make severe simplifications to the harmony or even change melodic intervals to fit what they have available. Audiences generally accept this because the strictures of the instrument have made that a common practice. (Even if you're unaware of the strictures, you've probably gotten used to hearing the result of the common practice.)
However, if one consistently employs major/minor triad substitutions on the guitar people are eventually going to hear that as a lack of quality. As in the Beach Boys example, this will often happen during key points. The guitarist may get lucky if the singer happens to fill out the missing note of the chord-- e.g., guitarist plays a minor triad and the singer fills out the seventh at the beginning of the chorus of "Last Dance with Mary Jane"-- but eventually the audience will figure out that the guitarist is missing a vital skill.
Anyway, unless your instrument is so novel it doesn't have any associations with extant instruments, make sure you have some kind of "escape hatch" so that skilled performers can play the chords they need. :)