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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.

LeaG
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  • Does this answer your question? [What does the chord notation X/Y ("slash chord") mean?](https://music.stackexchange.com/questions/104163/what-does-the-chord-notation-x-y-slash-chord-mean) – Aaron Feb 14 '23 at 08:34
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    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). – gingerbreadboy Feb 14 '23 at 09:46
  • `two different kinds` who am I kidding there are probably a dozen different uses for `slash` in chords and notation :) – gingerbreadboy Feb 14 '23 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 '23 at 10:13
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    @Aaron - not the slash chord question at all similar to the one quoted. OP is using RN. – Tim Feb 14 '23 at 10:15
  • @Tim This usage is covered in the answer and includes a link to another post with additional information. "In Functional Analysis (Roman Numeral Analysis), slashes are used to indicate a secondary dominant relationship. Secondary dominants are explained in [What is a secondary dominant chord?](https://music.stackexchange.com/q/22057/70803)." – Aaron Feb 14 '23 at 16:51

3 Answers3

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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'.

Tim
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  • Is this applicable to all scale degrees? For example could I analyse Bm as iii/V ("secondary mediant to the dominant")? – LeaG Feb 14 '23 at 19:57
  • I can only recall seeing dominants used in this way, V or vii – nuggethead Feb 14 '23 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 '23 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 '23 at 08:35
  • @LeaG - the point of secondary dominants id that they are dominants of of diatonic chords. iii/V would not constitute such. – Tim Feb 15 '23 at 08:37
  • @LeaG: If you really think that Bm is useful to describe as iii/V, maybe it would be better to think of V as tonic—maybe the song has temporarily modulated into a different key. – Dietrich Epp Feb 15 '23 at 21:28
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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.

Lazy
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    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 '23 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 '23 at 16:42
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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!

Laurence
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