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Note the position of the V6/5 in this progression. The introduction to vii7 involves understanding that vii7 can act as a substitute for a V6/5. |
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Voilà. This substitutes vii7 for V6/5. The only difference is the replacement of the 5th with a 6th—which replaces the common tone between V and I with a note which demands resolution. |
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The simplest, and most basic use of vii7 is in its capacity as a lower neighbor to the tonic. With ^5 in the soprano, the figure ^5-^6-^5 is almost inevitable given the opportunity to replicate the lower neighbor in the bass with upper neighbors in the other three voices. |
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In major keys, vii7 is naturally a half-diminished seventh chord, which is not altogether successful, at least not in the role of a neighbor. Therefore, ^6 is lowered a half step in order to provide a fully diminished sonority. It is traditional to avoid indicating the lowered seventh degree, using just the diminished sign instead in the analysis. |
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vii7 can be approached rather nicely from iv, since the common tone they share sets up the motion satisfactorily. |
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In major mode, motion from ii to vii7 works well, especially if you concentrate on maintaining the two common tones ^2 and ^4. |
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Obviously if you can move to vii7 from ii, then ii6 should work. Try to maintain at least one of the common tones; it’s best to maintain both if possible. |
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Motion from III in minor permits an alternate setting of ^3-^2-^1 in the soprano. Note that this will also work quite well in major. |
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Motion involving III to the natural form of VII, and thence to vii7. This setting is taking full advantage of the natural-^7-raised-^7-^1 motion in the bass, which serves to mask the undeniable cross-relation that exists in the outer voices on the third and fourth beats. Having the motion chromatically in the bass renders this progression acceptable. |
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Here is a very simple and effective demonstration of the essential similarity between V6/5 and vii7. |
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vii6/5 usually resolves upwards to I6/3—the tritone formed between the bass and the (diminished) fifth of the chord tends to require an inward resolution to a third. |
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Another example of the same idea, this time in minor. vii6/5 is acting more or less as a substitute for vii6. Thus note that vii6 can be swapped with V6/4 or vii6/5. |
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Motion from IV allows me to capitalize on the flat ^6 that is inherent in vii6/5 (along with all vii7’s and inversions). By keeping the motion ^6-flat^6 in the same voice I avoid cross relations. |
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In minor, motion from ii6/3 allows the exploration of multiple diminished chords. |
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The resolution of vii4/3 should take care with the diminished fifth—that it resolves to a third. |
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Frequently the flat ^6 characteristic of vii7 invites modal mixture in the following chords. |
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vii4/2 does an excellent job of preparing the dominant. Here it prepares a cadential 6/4 quite adroitly. |
