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I am learning chord functions in major scales and supposedly the iii chord has a tonic function. however, the chord has a leading tone so shouldn't it be considered a dominant chord?

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  • Since it's the relative minor of that V chord, maybe. But when one considers Imaj7, iii is 3/4 of the way there.
    – Tim
    Feb 3 at 17:10
  • What do you mean by leading tone? Its own? Or the LT of the key? The iii is a suitable sub for the I and creates the Maj7, this is probably why you said it has an LT. But it is also the rel min of the V as Tim stated. It can actually serve as a sub for both.
    – user50691
    Feb 3 at 17:41
  • Maybe according to some theory, the emperor has clothes. But in reality the emperor has no clothes and the iii chord doesn't end a tune like a I chord does. :) Feb 3 at 18:08
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The idea is from German theory.

I don't know that theory well, but apparently the mediant chord can have both tonic and dominant function. The reason would be the overlapping tones of the tonic (^3 and ^5) and dominant (^5 and ^7) chords.

My way of reconciling the leading tone ^7 being in a non-dominant chord (and also the dominant ^5 is in the mediant) is two-fold:

  • the ^3 degree has its basic identity as a member of the tonic chord
  • the absence of ^4 - which could provide a dominant seventh - makes the chord less emphatically a dominant.

In other words the real dominant identity is TI & FA (in solfege) or scale degrees ^7 & ^4. It may seem ironic but ^5 isn't so critical a factor, but keep in mind ^5 is in the tonic chord too; clearly not a dominant in that case. TI & RE make a good dominant. You might put it like this: the leading tone TI and the absence of potential tonic tones - for practical purposes FA or RE - make a clear dominant. Then SOL or ^5 provides... I suppose tonal stability.

Having said that I thought the German theory treated the mediant chord as a dominant and the submediant as a tonic. Using the English terminology of the Wikipedia page the relative relations of I/vi and V/iii are somehow more fundamental that the counter-relative relationship of I/iii.

I don't know how that theory is actually applied in analysis. I learned American theory where all seven scale degrees are discrete chords. I'm not sure how a analysis case is made for the mediant being either dominant (Dominantparallele) or tonic (Tonika-Gegenparallele.)

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