When trying to find the function of the B major chord in C major I found that it was listed as a "V/iii" chord in this online calculator. I have never seen this before and don't know what this means and what it suggests about the function. To be clear, not referring to inversion slash chords (C/G, Am/C etc.)

Numeral calculator on C major with the V/iii chord shown

I am quite new to RN analysis and any help would be greatly appreciated as I am unsure where to find such information online.

  • Does this answer your question? What does the chord notation X/Y ("slash chord") mean?
    – Aaron
    Feb 14, 2023 at 8:34
  • 8
    Careful. I respectfully believe Aaron is confusing two concepts. I think the above linked question is a different thing to what is being asked in the OP. There are two different kinds of "slashy" chord notations. Aaron's link is talking about "chord over bass" (Gmaj over E bass) but the OP (and the answers below) are about "secondary tonality" (the five of five, the five of four, etc). Feb 14, 2023 at 9:46
  • two different kinds who am I kidding there are probably a dozen different uses for slash in chords and notation :) Feb 14, 2023 at 10:05
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    @gingerbreadboy - generally there is the slash chord in letters, like C/E, which signify a C chord with E in the bass (1st inversion), and the one OP is asking about, - R.N. Two very usual. Can't think of the other ten...
    – Tim
    Feb 14, 2023 at 10:13
  • 2
    @Aaron - not the slash chord question at all similar to the one quoted. OP is using RN.
    – Tim
    Feb 14, 2023 at 10:15

3 Answers 3


iii in key C major is E minor. The V of that chord is B (or B7). B is non-diatonic, and is called the secondary dominant in that key. It can lead to Em, and often does, although, despite the allusion that it's going to, it often doesn't.

So, V/iii is the dominant of a diatonic chord from a particular key. Another example would be V/V,, where the 1st V represents D (or D7), which does often feature moving to the dominant of that key. The 'dominant of the dominant'.

  • Is this applicable to all scale degrees? For example could I analyse Bm as iii/V ("secondary mediant to the dominant")?
    – LeaG
    Feb 14, 2023 at 19:57
  • I can only recall seeing dominants used in this way, V or vii
    – nuggethead
    Feb 14, 2023 at 21:28
  • @LeaG only if it is a useful description. A chord with dominant function usually leads very strongly to its resolution and therefore it makes sense to describe it as relative to that chord (e.g. V/iii). Your example, iii of V, is a chord that for starters would be exceedingly rare (if you want to use this label you probably missed one or more modulations) but also, the iii of V usually does not have a very clear relationship to V itself, so even if you encounter those notes it most probably functions differently and should then also be described differently.
    – 11684
    Feb 14, 2023 at 21:38
  • @nuggethead - secondary dominants are seen V/ii, V/iii, V/V and V/vii. There's a possibility of V7/IV, as V7 there contains a non-diatonic b7. Need to verify that one!
    – Tim
    Feb 15, 2023 at 8:35
  • @LeaG - the point of secondary dominants id that they are dominants of of diatonic chords. iii/V would not constitute such.
    – Tim
    Feb 15, 2023 at 8:37

This notation is used to code secondary tonalities. V/iii then would be read as "the secondary dominant to the root iii (which in this case is B major to E minor)".

Generally the notation is function/key. Note though that B major does not necessarily have that function in the context of C major.

  • 3
    It's certainly true that V/iii means "the secondary dominant of the mediant," it's more commonly read as "five of three."
    – phoog
    Feb 14, 2023 at 11:13
  • @phoog: Indeed. Further, since the V of III and the V of the iii would both be the same chord (a VII with raised sharp accidentals on the third and fifth), there's no need to say "V of minor iii" to distinguish it from "V of III".
    – supercat
    Feb 15, 2023 at 16:42

V of iii. The dominant of iii, which in this case is Em. Quire a common progression.

Starting off in C major, you’ll also often come across D leading to G, V of V. Or E leading to Am, V of vi.

If B - Em results in a lengthy visit to Em, you’ll probably find it useful to re-designate Em as i. If the chord progression is ‘just passing through’ leave it as iii. A chromatic chord does not necessarily imply a new key centre.

B can also function as a dominant to C major - all three notes are ‘leading notes’ to those of the C triad!

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