Theory III

Secondary o7 Chords

Secondary o7 chords (also ø7 and o6) function just like secondary dominants, only the secondary function (and thus the tonicization of the diatonic chord) is now created through the fully-diminished sound of the o7 chord (or half-diminished, or diminished triad in first inversion).

 

  1. Any diatonic major or minor triad may be preceded by its secondary o7 (or sometimes ø7 or o6). Notice that this excludes diminished or augmented triads; thus there's no such thing as o7/iio or o7/viio, etc. Note carefully that it's possible to have a chord with both a sharp and a flat in it (for example, C# E G Bb).
  2. The possibilities are thus o7/x and its inversions, as well as ø7/x and its inversions. The ø7/x is most often used to embellish the dominant in a major key, thus: ø7/V. The o6/x (a secondary diminished triad) is also possible--generally in just this inversion.
  3. o7/x generally resolves to x; o65/x generally resolves to x (occasionally x6); o43/x generally resolves to x6; o42/x (rarely used but certainly possible) generally resolves to x64. The same resolution tendencies apply for ø7/x. o6/x generally resolves to x, or sometimes x6. By the way: double the bass note in the o6/x.
  4. Voice leading: the easiest thing to remember is that the root resolves up, and the other notes all resolve down. Be careful to avoid //5ths in the progression ø7/x--x. Composers sometimes resolve the third of the o7/x up, thus creating a doubled third in x--this is OK to do also. Note carefully that notes with added sharps usually resolve up, while those with added flats generally resolve down.
  5. Note that o7/V (or ø7/V, or o6/V) can progress to I64 (or i64) before moving on to its V, thus: o7/V -- I64 -- V -- I.
  6. Secondary o7 chords (also ø7 and o6) thus have at least one chromatically altered note (sometimes more). The chromatically altered note usually functions like a temporary or secondary leading tone. Just like the "regular" 7 intensifies the resolution to 1, this secondary leading tone intensifies motion to the temporary tonic.
  7. So, this means that you look for chromatically altered notes, determine whether they're part of a o7 (or ø7 or o6) chord (remember that it may be a "plain old secondary dominant"--V7/x), then check to see that it resolves to its "tonic" (in this case, root movement up a half step).

     

Spelling and writing them: given F: o7/ii, think: 1) ii is G. 2) Now write o7/ii on the note a half-step below G--it's built on F# (F# is the leading tone to G). 3) Write a o7 chord built on F# (remember that a o7 chord is stacked minor thirds): F# A C Eb is the chord.

Another example: D: ø65/V. 1) V is A. 2) ø7/V would be written on the note a half-step below A--it's built on G# (G# is the leading tone to A). 3) Write a ø7 chord built on G#: G# B D F# is the root position chord. 4) Since it's ø65/V, the B would be in the bass. So remember: They're built on the note a half-step below what they're "of".

Hearing them: By now, you're capable of hearing where chromatic chords occur. So, follow these steps: 1) determine where you hear chromatic chords; 2) determine whether they're major-minor (i.e. "plain old secondary dominants") or some other quality--especially fully- or half-diminished; 3) listen to where they resolve; 4) listen carefully to the bass motion to determine the inversion.

For example: you hear ??--ii. Identify the ii chord, then go back and determine that the secondary chord was fully diminished (i.e. it's o7/ii or some inversion thereof). Listen for the bass motion to determine the correct inversion. Memorize the following to help you:

 

  o7/x:  bass resolves up a half step (note the similarity to V65/x).


  o65/x: bass resolves down a whole step (similar to V43/x).


  o43/x: bass resolves down a half step if the chord of resolution is major; down a
         whole step if the chord of resolution is minor (note that this resolution is to
         a first-inversion chord; also note that this is identical to V42/x).


  o42/x: rare; bass resolves down a half step, and the resolution is to a second
         inversion (64) chord.

Some examples:

Click music to hear the examples.