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I'm reading a paper on music theory and I keep coming across names of chords expressed as a fraction - I/I, I/V, ii/I, etc. Based on the use of these names in the paper, I'm reading this as:

I/I: A major chord with root as the first note of the Ionian mode of the diatonic major scale.

I/V: A major chord with root as the first note of the Mixolydian mode of the diatonic major scale.

ii/I: A minor chord with root as the second note of the Ionian mode of the diatonic major scale.

Is my understanding correct? Is there a more efficient/complete way to read this notation? In case I want to see more examples and explanation of this, what should I search for?


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up vote 5 down vote accepted

This notation is used for tonicizations and modulations. They mark the function of the chord in the target key.

So, for instance, V/V is the fifth of the fifth, that is, dominant of the dominant. This chord is commonly called the "double dominant". It can be used for a modulation into the dominant key or for temporary tonicization of the dominant.

It could also be notated as II, and sometimes it is. But the V/V notation makes its function more obvious.

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so would there be instances when 'II' and 'V/V' would appear in the same song? To show that it was just using the supertonic chord in isolation using II, but to show modulation as in V/V ?Seems somewhat over the top to me. The OP's concept of slash chords is incorrect, then? – Tim Jun 5 '14 at 9:34
I don't see why not. Don't we use these symbols for analysis? And analysis is often open to debate. I use II chords with no intention of tonicizing V, for example to harmonize a Dorian #4 scale (popular in Turkish music). I would argue that labeling this usage as V/V would be just wrong. Of course someone else could argue otherwise and we would have two different analyses :) – cyco130 Jun 5 '14 at 10:03
If you are working in a Dorian #4 scale, then roman numerals are not really relevant, are they? They assume common practice tonality, where ii is minor, and V/V is major. – Robert Fink Jun 7 '14 at 0:27

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