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I was watching this video about chromatic mediants (the video calls them chromatic thirds for some reason). And it made me wonder what is it about thirds that makes them popular. So we talk about major and minor third intervals. But why isn't there talk of chromatic seconds, or fourths, or fifths, or other intervals apart from thirds?

For example, I find the Cminor chord to C#minor chord has the same kind of sound as well.

  • Of note is lesmizzle's comment in the linked video: "This material should not be referred to as "chromatic thirds". Chromatic 3rds are chromatic melodic lines harmonized in 3rds. The term you should be using is "chromatic mediants" which refers to the harmonic relationships you are describing." I believe you may be getting some terminology mixed up. – Dekkadeci Feb 7 at 6:22
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    I suspect it's because we have better names for those. 4ths and 5ths produce either diatonic chords or modal mixture/harmonic or melodic minor, and seconds are usually secondary dominants or modal mixture. But every situation is different, and there's no usual pattern! (Also, 6ths are 3rds, 7ths are seconds) – user45266 Feb 7 at 7:11
  • Interesting link! It's always fine to listen to someone explaining things that have been known for 200 years and you found them out only some decades ago without knowing what this is :) – Albrecht Hügli Feb 7 at 9:17
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Just 'unpack' the terminology and then re-apply it to your question.

'Chromatic Mediant'

The 'mediant' just means that the roots of the two chords are separated by a third. Starting from a tonic chord the other chord root found at a third ascending or descending is either the mediant or the submediant. Those two labels are just collapsed - for convenience - into one term mediant to mean two chord roots separated by a third.

The 'chromatic' just indicates something about the second chord is chromatically altered, either the root is lowered/raised (along with the fifth) or the third of the chord is lowered/raised.

You can apply the same idea but change mediant to another tone. For example, if we coin the term chromatic second or chromatic supertonic we could go from the I to ii in major and then make our chromatic alterations: lower the root and fifth to get a bII chord or raise the third and get a II chord. But, those two chords already have identities as the N6 and V/V chords respectively.

If we go from I to V and explore the same possibilities for a hypothetical chromatic dominant, we get...

  • lower the root and fifth: not a triad
  • raise the root and fifth: #v or enharmonically bvi
  • lower the third: v minor dominant, Mixolydian flavor
  • raise the third: not a triad

With the lowered third we get something already familiar.

With raising the root/fifth we get something different, something that really should not get any labeling as a dominant.

The other two are non-tertian.

But why isn't there talk of chromatic seconds, or fourths, or fifths, or other intervals apart from thirds?

You can explore questions like this and see where they lead.

Mostly these chords will be borrowed chords or secondary dominants, but there may be some novel things to explore.

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Why do we not have chromatic supertonics (2nds) and chromatic subdominants and chromatic dominants (4ths and 5ths)?

I suspect it's because we have better names for those. 4ths and 5ths produce either diatonic chords or modal mixture/harmonic or melodic minor, and seconds are usually secondary dominants or modal mixture. But every situation is different, and there's no usual pattern! (Also, 6ths are 3rds, 7ths are seconds).

The whole reason we end up calling the case with 3rds "Chromatic Mediants" is because none of the other names are great descriptors of this effect (the 3rds are the connectors between the two chords). The other cases, with 2nds, 4ths, and 5ths (and trivially unisons), are already either described quite well or quite useless. If you hear a I-II-♭VII progression as "chromatic supertonics", be my guest, but others prefer other, more useful terms, like modal mixture or secondary dominants, depending heavily on context.

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A mediant is implicit a third.

After most other degrees have diatonic function, what will remain?

There will be tritonus and minor seconds ... but these aren't thirds and they are not mediants.

minor seconds can be treated as N6 (the italian) and the tritonus as V7-5 substitution.

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The 3rd of a scale is called the mediant.

Tonic, Supertonic, Mediant, Subdominant, Dominant, Submediant, Leading Note, Tonic.

The video actually answers your question pretty clearly. Functional harmony has trouble explaining a major chord on the mediant (that's E major in the key of C) when it doesn't act as the dominant of A minor. And even worse trouble if we go up another major third to G#(Ab) major (mediant of the mediant?). But it sounds good. Similarly for minor third jumps. C to Eb we can explain as a borrowed chord from C minor. But another minor third to Gb?

So, here's something musicians wanted to do, but they felt uncomfortable that their 'theory' couldn't give permission. So they slapped a label on it 'Chromatic Mediant'. It's labelled and catalogued. Therefore permitted.

And that really is about it :-)

  • great stuff. funny enough I didn't realize a mediant was another name for a third. although you never explained other intervals. but I gather from the other comments it's because all other intervals are explained with tonal harmony. – foreyez Feb 7 at 16:10
  • Sort of. Tonal harmony has a dirty little habit of being content with a POSSIBLE explanation, even when it's the wrong one. III is V of vi. So that's all right, III goes in the list of 'things you're allowed to do' even when that ISN'T what it does. But that's mentioned in the video too. You're not slipping into your old fallacy of trying to learn ALL the theory rather than observing the music, are you? – Laurence Payne Feb 7 at 16:17
  • Yes, leading note to mediant is a perfect 5th if you're going down. A perfect 4th if you're going up. So? – Laurence Payne Feb 7 at 16:26
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    @foreyez, Mediant isn't an interval, it's a name for a tone within the key (in Solfege it's called MI.) If the roots moved from leading tone to mediant, the interval is a descending perfect fifth. – Michael Curtis Feb 7 at 16:37
  • @LaurencePayne, I'm trying to explain that Mediant doesn't necessarily mean a third. In the term chromatic mediant it just means the roots are a third asc/desc apart. – Michael Curtis Feb 7 at 16:39

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