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Does anyone know a textbook or some music theorist explaining subdominant/dominant chord functions in terms of the two chords being the tonics in subdominant/dominant keys?

Background: I was thinking on how a person can reach to an idea similar to tonic/subdominant/dominant (i.e. the three categories of chords which have different degrees of unstableness) just by interval/key relationships, not by historical theories.

My current idea follows like this:

  • Harmonic series convince us that major chords are more consonant than minor chords or diminished chords because major chords appear as the 4/5/6th overtones.
  • A major diatonic scale (e.g. C major scale) can build three major triads, three minor triads, and one diminished triad. By major triads being more consonant, we can ignore less important parts (minor triads and diminished triad) and are interested in how the remaining three major triads relate to each other.
  • Among the three major triads, "triad whose root is the major scale's first note" (e.g. C major chord in the case of C major key) sounds most stable, given that the first note in the major scale is the most stable note. As a result, tonic chord is now considered as the most stable chord.
  • Then, we can observe that the remaining two major chords, one starting from the 4th note and the other from the 5th note, are also the tonic chord of other keys (e.g. F major key and G major key). The two chords are "the most stable" in those keys, but because we're currently thinking in a different key (e.g. C major key), they are currently used in an "unstable" way. Like in the middle of modulation or something.
  • Since we can't consider the two major chords as having the same quality (one being the right of the tonic chord in the circle of fifth, and the other being the left), we name it differently based on the names of keys: subdominant chord and dominant chord.

The reason I'm thinking about this is because I'm guessing thinking in tonic/subdominant/dominant keys in parallel may lead me understand some non-traditional chord progression, like IV-I-IV-I, better (IV-I-IV-I in tonic key is V-I-V-I in subdominant key) and may work as a more handy way to think when I compose a song.

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  • I don't understand the question. It sounds like you're describing the theory of modulation.
    – Aaron
    Nov 24 '20 at 8:47
  • Sorry my explanation may not be clear. I think what I was asking is if there is any textbook explaining subdominant/dominant functions by different keys. Those two concepts often suddenly appear without any justification (such as why not mentioning ii, iii, iv chords or why V are more unstable than IV), and I'd like to see if others introduce subdominant/dominant functions with respect to other keys. @Aaron does this make sense, or is my question still unclear?
    – sonicom
    Nov 24 '20 at 9:09
  • I think you just need a better music theory textbook. V is more unstable than IV, because it contains the leading tone, and scale degrees 2 and 7 are more dissonant with the tonic than are 4 and 6. ii, iii, and iv are all mentioned, but usually in later chapters, because their principal functions are derived from the dominant and subdominant functions.
    – Aaron
    Nov 24 '20 at 9:14
  • It's very difficut to find exactly what you're asking here. The relationship between I and IV is the same as that between V and I, in different keys, for example, but I don't think many composers refer directly to theory while they're writing. It may be used as a technical guide.
    – Tim
    Nov 24 '20 at 9:18
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    "IV-I-IV-I in tonic key is V-I-V-I in subdominant key" – no. It is I-V-I-V in subdominant key. But you are not free to choose the key in which you interpret music. Tonal center resolves tension, and very often can be identified ambiguously. You seem to be skipping the aspect of tension entirely. Nov 24 '20 at 15:22
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Let me first confirm your question. You want to think of a chord or chords in more than one key at a time. Or, in other words, you want to keep track of what one progression would be from the perspective of other keys. To clarify, you want to use the exact same chords from one key in another key.

This is a good skill to have and aspects of this come up quite strongly in Gottfried Weber's music theory. He describes this phenomenon as "multiple meaning." You may want to check out his work. You certainly raise a good and valid question, please do not remove your post from the forum.

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    Indeed, his "Theory of Musical Composition" exactly answered my question. The book not only answered my question but also expanded the idea of multiple interpretations to notes, intervals, or chord symbols. Super educative. Thanks for sharing an inspirational resource!
    – sonicom
    Nov 26 '20 at 3:22

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